e1e72965ec
Went through the documentation doing typo and content fixes. This patch contains only comment and whitespace changes. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
1073 lines
40 KiB
C
1073 lines
40 KiB
C
/*P:010
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* A hypervisor allows multiple Operating Systems to run on a single machine.
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* To quote David Wheeler: "Any problem in computer science can be solved with
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* another layer of indirection."
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*
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* We keep things simple in two ways. First, we start with a normal Linux
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* kernel and insert a module (lg.ko) which allows us to run other Linux
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* kernels the same way we'd run processes. We call the first kernel the Host,
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* and the others the Guests. The program which sets up and configures Guests
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* (such as the example in Documentation/lguest/lguest.c) is called the
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* Launcher.
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*
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* Secondly, we only run specially modified Guests, not normal kernels. When
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* you set CONFIG_LGUEST to 'y' or 'm', this automatically sets
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* CONFIG_LGUEST_GUEST=y, which compiles this file into the kernel so it knows
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* how to be a Guest. This means that you can use the same kernel you boot
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* normally (ie. as a Host) as a Guest.
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*
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* These Guests know that they cannot do privileged operations, such as disable
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* interrupts, and that they have to ask the Host to do such things explicitly.
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* This file consists of all the replacements for such low-level native
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* hardware operations: these special Guest versions call the Host.
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*
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* So how does the kernel know it's a Guest? The Guest starts at a special
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* entry point marked with a magic string, which sets up a few things then
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* calls here. We replace the native functions various "paravirt" structures
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* with our Guest versions, then boot like normal. :*/
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/*
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* Copyright (C) 2006, Rusty Russell <rusty@rustcorp.com.au> IBM Corporation.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
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* NON INFRINGEMENT. See the GNU General Public License for more
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* details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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#include <linux/kernel.h>
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#include <linux/start_kernel.h>
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#include <linux/string.h>
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#include <linux/console.h>
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#include <linux/screen_info.h>
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#include <linux/irq.h>
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#include <linux/interrupt.h>
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#include <linux/clocksource.h>
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#include <linux/clockchips.h>
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#include <linux/lguest.h>
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#include <linux/lguest_launcher.h>
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#include <linux/virtio_console.h>
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#include <linux/pm.h>
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#include <asm/paravirt.h>
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#include <asm/param.h>
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#include <asm/page.h>
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#include <asm/pgtable.h>
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#include <asm/desc.h>
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#include <asm/setup.h>
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#include <asm/e820.h>
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#include <asm/mce.h>
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#include <asm/io.h>
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#include <asm/i387.h>
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/*G:010 Welcome to the Guest!
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*
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* The Guest in our tale is a simple creature: identical to the Host but
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* behaving in simplified but equivalent ways. In particular, the Guest is the
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* same kernel as the Host (or at least, built from the same source code). :*/
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/* Declarations for definitions in lguest_guest.S */
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extern char lguest_noirq_start[], lguest_noirq_end[];
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extern const char lgstart_cli[], lgend_cli[];
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extern const char lgstart_sti[], lgend_sti[];
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extern const char lgstart_popf[], lgend_popf[];
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extern const char lgstart_pushf[], lgend_pushf[];
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extern const char lgstart_iret[], lgend_iret[];
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extern void lguest_iret(void);
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struct lguest_data lguest_data = {
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.hcall_status = { [0 ... LHCALL_RING_SIZE-1] = 0xFF },
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.noirq_start = (u32)lguest_noirq_start,
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.noirq_end = (u32)lguest_noirq_end,
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.kernel_address = PAGE_OFFSET,
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.blocked_interrupts = { 1 }, /* Block timer interrupts */
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.syscall_vec = SYSCALL_VECTOR,
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};
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static cycle_t clock_base;
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/*G:035 Notice the lazy_hcall() above, rather than hcall(). This is our first
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* real optimization trick!
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*
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* When lazy_mode is set, it means we're allowed to defer all hypercalls and do
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* them as a batch when lazy_mode is eventually turned off. Because hypercalls
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* are reasonably expensive, batching them up makes sense. For example, a
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* large munmap might update dozens of page table entries: that code calls
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* paravirt_enter_lazy_mmu(), does the dozen updates, then calls
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* lguest_leave_lazy_mode().
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*
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* So, when we're in lazy mode, we call async_hypercall() to store the call for
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* future processing. When lazy mode is turned off we issue a hypercall to
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* flush the stored calls.
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*/
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static void lguest_leave_lazy_mode(void)
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{
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paravirt_leave_lazy(paravirt_get_lazy_mode());
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hcall(LHCALL_FLUSH_ASYNC, 0, 0, 0);
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}
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static void lazy_hcall(unsigned long call,
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unsigned long arg1,
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unsigned long arg2,
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unsigned long arg3)
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{
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if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE)
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hcall(call, arg1, arg2, arg3);
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else
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async_hcall(call, arg1, arg2, arg3);
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}
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/* async_hcall() is pretty simple: I'm quite proud of it really. We have a
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* ring buffer of stored hypercalls which the Host will run though next time we
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* do a normal hypercall. Each entry in the ring has 4 slots for the hypercall
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* arguments, and a "hcall_status" word which is 0 if the call is ready to go,
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* and 255 once the Host has finished with it.
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*
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* If we come around to a slot which hasn't been finished, then the table is
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* full and we just make the hypercall directly. This has the nice side
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* effect of causing the Host to run all the stored calls in the ring buffer
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* which empties it for next time! */
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void async_hcall(unsigned long call,
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unsigned long arg1, unsigned long arg2, unsigned long arg3)
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{
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/* Note: This code assumes we're uniprocessor. */
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static unsigned int next_call;
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unsigned long flags;
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/* Disable interrupts if not already disabled: we don't want an
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* interrupt handler making a hypercall while we're already doing
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* one! */
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local_irq_save(flags);
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if (lguest_data.hcall_status[next_call] != 0xFF) {
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/* Table full, so do normal hcall which will flush table. */
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hcall(call, arg1, arg2, arg3);
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} else {
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lguest_data.hcalls[next_call].arg0 = call;
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lguest_data.hcalls[next_call].arg1 = arg1;
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lguest_data.hcalls[next_call].arg2 = arg2;
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lguest_data.hcalls[next_call].arg3 = arg3;
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/* Arguments must all be written before we mark it to go */
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wmb();
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lguest_data.hcall_status[next_call] = 0;
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if (++next_call == LHCALL_RING_SIZE)
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next_call = 0;
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}
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local_irq_restore(flags);
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}
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/*:*/
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/*G:033
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* After that diversion we return to our first native-instruction
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* replacements: four functions for interrupt control.
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*
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* The simplest way of implementing these would be to have "turn interrupts
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* off" and "turn interrupts on" hypercalls. Unfortunately, this is too slow:
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* these are by far the most commonly called functions of those we override.
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*
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* So instead we keep an "irq_enabled" field inside our "struct lguest_data",
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* which the Guest can update with a single instruction. The Host knows to
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* check there when it wants to deliver an interrupt.
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*/
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/* save_flags() is expected to return the processor state (ie. "eflags"). The
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* eflags word contains all kind of stuff, but in practice Linux only cares
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* about the interrupt flag. Our "save_flags()" just returns that. */
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static unsigned long save_fl(void)
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{
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return lguest_data.irq_enabled;
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}
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/* restore_flags() just sets the flags back to the value given. */
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static void restore_fl(unsigned long flags)
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{
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lguest_data.irq_enabled = flags;
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}
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/* Interrupts go off... */
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static void irq_disable(void)
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{
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lguest_data.irq_enabled = 0;
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}
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/* Interrupts go on... */
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static void irq_enable(void)
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{
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lguest_data.irq_enabled = X86_EFLAGS_IF;
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}
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/*:*/
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/*M:003 Note that we don't check for outstanding interrupts when we re-enable
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* them (or when we unmask an interrupt). This seems to work for the moment,
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* since interrupts are rare and we'll just get the interrupt on the next timer
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* tick, but when we turn on CONFIG_NO_HZ, we should revisit this. One way
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* would be to put the "irq_enabled" field in a page by itself, and have the
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* Host write-protect it when an interrupt comes in when irqs are disabled.
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* There will then be a page fault as soon as interrupts are re-enabled. :*/
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/*G:034
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* The Interrupt Descriptor Table (IDT).
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*
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* The IDT tells the processor what to do when an interrupt comes in. Each
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* entry in the table is a 64-bit descriptor: this holds the privilege level,
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* address of the handler, and... well, who cares? The Guest just asks the
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* Host to make the change anyway, because the Host controls the real IDT.
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*/
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static void lguest_write_idt_entry(struct desc_struct *dt,
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int entrynum, u32 low, u32 high)
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{
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/* Keep the local copy up to date. */
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write_dt_entry(dt, entrynum, low, high);
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/* Tell Host about this new entry. */
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hcall(LHCALL_LOAD_IDT_ENTRY, entrynum, low, high);
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}
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/* Changing to a different IDT is very rare: we keep the IDT up-to-date every
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* time it is written, so we can simply loop through all entries and tell the
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* Host about them. */
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static void lguest_load_idt(const struct Xgt_desc_struct *desc)
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{
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unsigned int i;
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struct desc_struct *idt = (void *)desc->address;
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for (i = 0; i < (desc->size+1)/8; i++)
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hcall(LHCALL_LOAD_IDT_ENTRY, i, idt[i].a, idt[i].b);
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}
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/*
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* The Global Descriptor Table.
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*
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* The Intel architecture defines another table, called the Global Descriptor
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* Table (GDT). You tell the CPU where it is (and its size) using the "lgdt"
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* instruction, and then several other instructions refer to entries in the
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* table. There are three entries which the Switcher needs, so the Host simply
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* controls the entire thing and the Guest asks it to make changes using the
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* LOAD_GDT hypercall.
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*
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* This is the opposite of the IDT code where we have a LOAD_IDT_ENTRY
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* hypercall and use that repeatedly to load a new IDT. I don't think it
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* really matters, but wouldn't it be nice if they were the same?
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*/
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static void lguest_load_gdt(const struct Xgt_desc_struct *desc)
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{
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BUG_ON((desc->size+1)/8 != GDT_ENTRIES);
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hcall(LHCALL_LOAD_GDT, __pa(desc->address), GDT_ENTRIES, 0);
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}
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/* For a single GDT entry which changes, we do the lazy thing: alter our GDT,
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* then tell the Host to reload the entire thing. This operation is so rare
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* that this naive implementation is reasonable. */
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static void lguest_write_gdt_entry(struct desc_struct *dt,
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int entrynum, u32 low, u32 high)
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{
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write_dt_entry(dt, entrynum, low, high);
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hcall(LHCALL_LOAD_GDT, __pa(dt), GDT_ENTRIES, 0);
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}
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/* OK, I lied. There are three "thread local storage" GDT entries which change
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* on every context switch (these three entries are how glibc implements
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* __thread variables). So we have a hypercall specifically for this case. */
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static void lguest_load_tls(struct thread_struct *t, unsigned int cpu)
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{
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/* There's one problem which normal hardware doesn't have: the Host
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* can't handle us removing entries we're currently using. So we clear
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* the GS register here: if it's needed it'll be reloaded anyway. */
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loadsegment(gs, 0);
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lazy_hcall(LHCALL_LOAD_TLS, __pa(&t->tls_array), cpu, 0);
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}
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/*G:038 That's enough excitement for now, back to ploughing through each of
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* the different pv_ops structures (we're about 1/3 of the way through).
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*
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* This is the Local Descriptor Table, another weird Intel thingy. Linux only
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* uses this for some strange applications like Wine. We don't do anything
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* here, so they'll get an informative and friendly Segmentation Fault. */
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static void lguest_set_ldt(const void *addr, unsigned entries)
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{
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}
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/* This loads a GDT entry into the "Task Register": that entry points to a
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* structure called the Task State Segment. Some comments scattered though the
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* kernel code indicate that this used for task switching in ages past, along
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* with blood sacrifice and astrology.
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*
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* Now there's nothing interesting in here that we don't get told elsewhere.
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* But the native version uses the "ltr" instruction, which makes the Host
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* complain to the Guest about a Segmentation Fault and it'll oops. So we
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* override the native version with a do-nothing version. */
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static void lguest_load_tr_desc(void)
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{
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}
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/* The "cpuid" instruction is a way of querying both the CPU identity
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* (manufacturer, model, etc) and its features. It was introduced before the
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* Pentium in 1993 and keeps getting extended by both Intel and AMD. As you
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* might imagine, after a decade and a half this treatment, it is now a giant
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* ball of hair. Its entry in the current Intel manual runs to 28 pages.
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*
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* This instruction even it has its own Wikipedia entry. The Wikipedia entry
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* has been translated into 4 languages. I am not making this up!
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*
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* We could get funky here and identify ourselves as "GenuineLguest", but
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* instead we just use the real "cpuid" instruction. Then I pretty much turned
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* off feature bits until the Guest booted. (Don't say that: you'll damage
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* lguest sales!) Shut up, inner voice! (Hey, just pointing out that this is
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* hardly future proof.) Noone's listening! They don't like you anyway,
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* parenthetic weirdo!
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*
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* Replacing the cpuid so we can turn features off is great for the kernel, but
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* anyone (including userspace) can just use the raw "cpuid" instruction and
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* the Host won't even notice since it isn't privileged. So we try not to get
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* too worked up about it. */
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static void lguest_cpuid(unsigned int *eax, unsigned int *ebx,
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unsigned int *ecx, unsigned int *edx)
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{
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int function = *eax;
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native_cpuid(eax, ebx, ecx, edx);
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switch (function) {
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case 1: /* Basic feature request. */
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/* We only allow kernel to see SSE3, CMPXCHG16B and SSSE3 */
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*ecx &= 0x00002201;
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/* SSE, SSE2, FXSR, MMX, CMOV, CMPXCHG8B, FPU. */
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*edx &= 0x07808101;
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/* The Host can do a nice optimization if it knows that the
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* kernel mappings (addresses above 0xC0000000 or whatever
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* PAGE_OFFSET is set to) haven't changed. But Linux calls
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* flush_tlb_user() for both user and kernel mappings unless
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* the Page Global Enable (PGE) feature bit is set. */
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*edx |= 0x00002000;
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break;
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case 0x80000000:
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/* Futureproof this a little: if they ask how much extended
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* processor information there is, limit it to known fields. */
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if (*eax > 0x80000008)
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*eax = 0x80000008;
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break;
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}
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}
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/* Intel has four control registers, imaginatively named cr0, cr2, cr3 and cr4.
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* I assume there's a cr1, but it hasn't bothered us yet, so we'll not bother
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* it. The Host needs to know when the Guest wants to change them, so we have
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* a whole series of functions like read_cr0() and write_cr0().
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*
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* We start with cr0. cr0 allows you to turn on and off all kinds of basic
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* features, but Linux only really cares about one: the horrifically-named Task
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* Switched (TS) bit at bit 3 (ie. 8)
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*
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* What does the TS bit do? Well, it causes the CPU to trap (interrupt 7) if
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* the floating point unit is used. Which allows us to restore FPU state
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* lazily after a task switch, and Linux uses that gratefully, but wouldn't a
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* name like "FPUTRAP bit" be a little less cryptic?
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*
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* We store cr0 (and cr3) locally, because the Host never changes it. The
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* Guest sometimes wants to read it and we'd prefer not to bother the Host
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* unnecessarily. */
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static unsigned long current_cr0, current_cr3;
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static void lguest_write_cr0(unsigned long val)
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{
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lazy_hcall(LHCALL_TS, val & X86_CR0_TS, 0, 0);
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current_cr0 = val;
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}
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static unsigned long lguest_read_cr0(void)
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{
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return current_cr0;
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}
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/* Intel provided a special instruction to clear the TS bit for people too cool
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* to use write_cr0() to do it. This "clts" instruction is faster, because all
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* the vowels have been optimized out. */
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static void lguest_clts(void)
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{
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lazy_hcall(LHCALL_TS, 0, 0, 0);
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current_cr0 &= ~X86_CR0_TS;
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}
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/* cr2 is the virtual address of the last page fault, which the Guest only ever
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* reads. The Host kindly writes this into our "struct lguest_data", so we
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* just read it out of there. */
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static unsigned long lguest_read_cr2(void)
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{
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return lguest_data.cr2;
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}
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/* cr3 is the current toplevel pagetable page: the principle is the same as
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* cr0. Keep a local copy, and tell the Host when it changes. */
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static void lguest_write_cr3(unsigned long cr3)
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{
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lazy_hcall(LHCALL_NEW_PGTABLE, cr3, 0, 0);
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current_cr3 = cr3;
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}
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static unsigned long lguest_read_cr3(void)
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{
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return current_cr3;
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}
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/* cr4 is used to enable and disable PGE, but we don't care. */
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static unsigned long lguest_read_cr4(void)
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{
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return 0;
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}
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static void lguest_write_cr4(unsigned long val)
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{
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}
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/*
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* Page Table Handling.
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*
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* Now would be a good time to take a rest and grab a coffee or similarly
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* relaxing stimulant. The easy parts are behind us, and the trek gradually
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* winds uphill from here.
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*
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* Quick refresher: memory is divided into "pages" of 4096 bytes each. The CPU
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* maps virtual addresses to physical addresses using "page tables". We could
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* use one huge index of 1 million entries: each address is 4 bytes, so that's
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* 1024 pages just to hold the page tables. But since most virtual addresses
|
|
* are unused, we use a two level index which saves space. The cr3 register
|
|
* contains the physical address of the top level "page directory" page, which
|
|
* contains physical addresses of up to 1024 second-level pages. Each of these
|
|
* second level pages contains up to 1024 physical addresses of actual pages,
|
|
* or Page Table Entries (PTEs).
|
|
*
|
|
* Here's a diagram, where arrows indicate physical addresses:
|
|
*
|
|
* cr3 ---> +---------+
|
|
* | --------->+---------+
|
|
* | | | PADDR1 |
|
|
* Top-level | | PADDR2 |
|
|
* (PMD) page | | |
|
|
* | | Lower-level |
|
|
* | | (PTE) page |
|
|
* | | | |
|
|
* .... ....
|
|
*
|
|
* So to convert a virtual address to a physical address, we look up the top
|
|
* level, which points us to the second level, which gives us the physical
|
|
* address of that page. If the top level entry was not present, or the second
|
|
* level entry was not present, then the virtual address is invalid (we
|
|
* say "the page was not mapped").
|
|
*
|
|
* Put another way, a 32-bit virtual address is divided up like so:
|
|
*
|
|
* 1 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
|
|
* |<---- 10 bits ---->|<---- 10 bits ---->|<------ 12 bits ------>|
|
|
* Index into top Index into second Offset within page
|
|
* page directory page pagetable page
|
|
*
|
|
* The kernel spends a lot of time changing both the top-level page directory
|
|
* and lower-level pagetable pages. The Guest doesn't know physical addresses,
|
|
* so while it maintains these page tables exactly like normal, it also needs
|
|
* to keep the Host informed whenever it makes a change: the Host will create
|
|
* the real page tables based on the Guests'.
|
|
*/
|
|
|
|
/* The Guest calls this to set a second-level entry (pte), ie. to map a page
|
|
* into a process' address space. We set the entry then tell the Host the
|
|
* toplevel and address this corresponds to. The Guest uses one pagetable per
|
|
* process, so we need to tell the Host which one we're changing (mm->pgd). */
|
|
static void lguest_set_pte_at(struct mm_struct *mm, unsigned long addr,
|
|
pte_t *ptep, pte_t pteval)
|
|
{
|
|
*ptep = pteval;
|
|
lazy_hcall(LHCALL_SET_PTE, __pa(mm->pgd), addr, pteval.pte_low);
|
|
}
|
|
|
|
/* The Guest calls this to set a top-level entry. Again, we set the entry then
|
|
* tell the Host which top-level page we changed, and the index of the entry we
|
|
* changed. */
|
|
static void lguest_set_pmd(pmd_t *pmdp, pmd_t pmdval)
|
|
{
|
|
*pmdp = pmdval;
|
|
lazy_hcall(LHCALL_SET_PMD, __pa(pmdp)&PAGE_MASK,
|
|
(__pa(pmdp)&(PAGE_SIZE-1))/4, 0);
|
|
}
|
|
|
|
/* There are a couple of legacy places where the kernel sets a PTE, but we
|
|
* don't know the top level any more. This is useless for us, since we don't
|
|
* know which pagetable is changing or what address, so we just tell the Host
|
|
* to forget all of them. Fortunately, this is very rare.
|
|
*
|
|
* ... except in early boot when the kernel sets up the initial pagetables,
|
|
* which makes booting astonishingly slow. So we don't even tell the Host
|
|
* anything changed until we've done the first page table switch. */
|
|
static void lguest_set_pte(pte_t *ptep, pte_t pteval)
|
|
{
|
|
*ptep = pteval;
|
|
/* Don't bother with hypercall before initial setup. */
|
|
if (current_cr3)
|
|
lazy_hcall(LHCALL_FLUSH_TLB, 1, 0, 0);
|
|
}
|
|
|
|
/* Unfortunately for Lguest, the pv_mmu_ops for page tables were based on
|
|
* native page table operations. On native hardware you can set a new page
|
|
* table entry whenever you want, but if you want to remove one you have to do
|
|
* a TLB flush (a TLB is a little cache of page table entries kept by the CPU).
|
|
*
|
|
* So the lguest_set_pte_at() and lguest_set_pmd() functions above are only
|
|
* called when a valid entry is written, not when it's removed (ie. marked not
|
|
* present). Instead, this is where we come when the Guest wants to remove a
|
|
* page table entry: we tell the Host to set that entry to 0 (ie. the present
|
|
* bit is zero). */
|
|
static void lguest_flush_tlb_single(unsigned long addr)
|
|
{
|
|
/* Simply set it to zero: if it was not, it will fault back in. */
|
|
lazy_hcall(LHCALL_SET_PTE, current_cr3, addr, 0);
|
|
}
|
|
|
|
/* This is what happens after the Guest has removed a large number of entries.
|
|
* This tells the Host that any of the page table entries for userspace might
|
|
* have changed, ie. virtual addresses below PAGE_OFFSET. */
|
|
static void lguest_flush_tlb_user(void)
|
|
{
|
|
lazy_hcall(LHCALL_FLUSH_TLB, 0, 0, 0);
|
|
}
|
|
|
|
/* This is called when the kernel page tables have changed. That's not very
|
|
* common (unless the Guest is using highmem, which makes the Guest extremely
|
|
* slow), so it's worth separating this from the user flushing above. */
|
|
static void lguest_flush_tlb_kernel(void)
|
|
{
|
|
lazy_hcall(LHCALL_FLUSH_TLB, 1, 0, 0);
|
|
}
|
|
|
|
/*
|
|
* The Unadvanced Programmable Interrupt Controller.
|
|
*
|
|
* This is an attempt to implement the simplest possible interrupt controller.
|
|
* I spent some time looking though routines like set_irq_chip_and_handler,
|
|
* set_irq_chip_and_handler_name, set_irq_chip_data and set_phasers_to_stun and
|
|
* I *think* this is as simple as it gets.
|
|
*
|
|
* We can tell the Host what interrupts we want blocked ready for using the
|
|
* lguest_data.interrupts bitmap, so disabling (aka "masking") them is as
|
|
* simple as setting a bit. We don't actually "ack" interrupts as such, we
|
|
* just mask and unmask them. I wonder if we should be cleverer?
|
|
*/
|
|
static void disable_lguest_irq(unsigned int irq)
|
|
{
|
|
set_bit(irq, lguest_data.blocked_interrupts);
|
|
}
|
|
|
|
static void enable_lguest_irq(unsigned int irq)
|
|
{
|
|
clear_bit(irq, lguest_data.blocked_interrupts);
|
|
}
|
|
|
|
/* This structure describes the lguest IRQ controller. */
|
|
static struct irq_chip lguest_irq_controller = {
|
|
.name = "lguest",
|
|
.mask = disable_lguest_irq,
|
|
.mask_ack = disable_lguest_irq,
|
|
.unmask = enable_lguest_irq,
|
|
};
|
|
|
|
/* This sets up the Interrupt Descriptor Table (IDT) entry for each hardware
|
|
* interrupt (except 128, which is used for system calls), and then tells the
|
|
* Linux infrastructure that each interrupt is controlled by our level-based
|
|
* lguest interrupt controller. */
|
|
static void __init lguest_init_IRQ(void)
|
|
{
|
|
unsigned int i;
|
|
|
|
for (i = 0; i < LGUEST_IRQS; i++) {
|
|
int vector = FIRST_EXTERNAL_VECTOR + i;
|
|
if (vector != SYSCALL_VECTOR) {
|
|
set_intr_gate(vector, interrupt[i]);
|
|
set_irq_chip_and_handler(i, &lguest_irq_controller,
|
|
handle_level_irq);
|
|
}
|
|
}
|
|
/* This call is required to set up for 4k stacks, where we have
|
|
* separate stacks for hard and soft interrupts. */
|
|
irq_ctx_init(smp_processor_id());
|
|
}
|
|
|
|
/*
|
|
* Time.
|
|
*
|
|
* It would be far better for everyone if the Guest had its own clock, but
|
|
* until then the Host gives us the time on every interrupt.
|
|
*/
|
|
static unsigned long lguest_get_wallclock(void)
|
|
{
|
|
return lguest_data.time.tv_sec;
|
|
}
|
|
|
|
static cycle_t lguest_clock_read(void)
|
|
{
|
|
unsigned long sec, nsec;
|
|
|
|
/* If the Host tells the TSC speed, we can trust that. */
|
|
if (lguest_data.tsc_khz)
|
|
return native_read_tsc();
|
|
|
|
/* If we can't use the TSC, we read the time value written by the Host.
|
|
* Since it's in two parts (seconds and nanoseconds), we risk reading
|
|
* it just as it's changing from 99 & 0.999999999 to 100 and 0, and
|
|
* getting 99 and 0. As Linux tends to come apart under the stress of
|
|
* time travel, we must be careful: */
|
|
do {
|
|
/* First we read the seconds part. */
|
|
sec = lguest_data.time.tv_sec;
|
|
/* This read memory barrier tells the compiler and the CPU that
|
|
* this can't be reordered: we have to complete the above
|
|
* before going on. */
|
|
rmb();
|
|
/* Now we read the nanoseconds part. */
|
|
nsec = lguest_data.time.tv_nsec;
|
|
/* Make sure we've done that. */
|
|
rmb();
|
|
/* Now if the seconds part has changed, try again. */
|
|
} while (unlikely(lguest_data.time.tv_sec != sec));
|
|
|
|
/* Our non-TSC clock is in real nanoseconds. */
|
|
return sec*1000000000ULL + nsec;
|
|
}
|
|
|
|
/* This is what we tell the kernel is our clocksource. */
|
|
static struct clocksource lguest_clock = {
|
|
.name = "lguest",
|
|
.rating = 400,
|
|
.read = lguest_clock_read,
|
|
.mask = CLOCKSOURCE_MASK(64),
|
|
.mult = 1 << 22,
|
|
.shift = 22,
|
|
.flags = CLOCK_SOURCE_IS_CONTINUOUS,
|
|
};
|
|
|
|
/* The "scheduler clock" is just our real clock, adjusted to start at zero */
|
|
static unsigned long long lguest_sched_clock(void)
|
|
{
|
|
return cyc2ns(&lguest_clock, lguest_clock_read() - clock_base);
|
|
}
|
|
|
|
/* We also need a "struct clock_event_device": Linux asks us to set it to go
|
|
* off some time in the future. Actually, James Morris figured all this out, I
|
|
* just applied the patch. */
|
|
static int lguest_clockevent_set_next_event(unsigned long delta,
|
|
struct clock_event_device *evt)
|
|
{
|
|
if (delta < LG_CLOCK_MIN_DELTA) {
|
|
if (printk_ratelimit())
|
|
printk(KERN_DEBUG "%s: small delta %lu ns\n",
|
|
__FUNCTION__, delta);
|
|
return -ETIME;
|
|
}
|
|
hcall(LHCALL_SET_CLOCKEVENT, delta, 0, 0);
|
|
return 0;
|
|
}
|
|
|
|
static void lguest_clockevent_set_mode(enum clock_event_mode mode,
|
|
struct clock_event_device *evt)
|
|
{
|
|
switch (mode) {
|
|
case CLOCK_EVT_MODE_UNUSED:
|
|
case CLOCK_EVT_MODE_SHUTDOWN:
|
|
/* A 0 argument shuts the clock down. */
|
|
hcall(LHCALL_SET_CLOCKEVENT, 0, 0, 0);
|
|
break;
|
|
case CLOCK_EVT_MODE_ONESHOT:
|
|
/* This is what we expect. */
|
|
break;
|
|
case CLOCK_EVT_MODE_PERIODIC:
|
|
BUG();
|
|
case CLOCK_EVT_MODE_RESUME:
|
|
break;
|
|
}
|
|
}
|
|
|
|
/* This describes our primitive timer chip. */
|
|
static struct clock_event_device lguest_clockevent = {
|
|
.name = "lguest",
|
|
.features = CLOCK_EVT_FEAT_ONESHOT,
|
|
.set_next_event = lguest_clockevent_set_next_event,
|
|
.set_mode = lguest_clockevent_set_mode,
|
|
.rating = INT_MAX,
|
|
.mult = 1,
|
|
.shift = 0,
|
|
.min_delta_ns = LG_CLOCK_MIN_DELTA,
|
|
.max_delta_ns = LG_CLOCK_MAX_DELTA,
|
|
};
|
|
|
|
/* This is the Guest timer interrupt handler (hardware interrupt 0). We just
|
|
* call the clockevent infrastructure and it does whatever needs doing. */
|
|
static void lguest_time_irq(unsigned int irq, struct irq_desc *desc)
|
|
{
|
|
unsigned long flags;
|
|
|
|
/* Don't interrupt us while this is running. */
|
|
local_irq_save(flags);
|
|
lguest_clockevent.event_handler(&lguest_clockevent);
|
|
local_irq_restore(flags);
|
|
}
|
|
|
|
/* At some point in the boot process, we get asked to set up our timing
|
|
* infrastructure. The kernel doesn't expect timer interrupts before this, but
|
|
* we cleverly initialized the "blocked_interrupts" field of "struct
|
|
* lguest_data" so that timer interrupts were blocked until now. */
|
|
static void lguest_time_init(void)
|
|
{
|
|
/* Set up the timer interrupt (0) to go to our simple timer routine */
|
|
set_irq_handler(0, lguest_time_irq);
|
|
|
|
/* Our clock structure looks like arch/x86/kernel/tsc_32.c if we can
|
|
* use the TSC, otherwise it's a dumb nanosecond-resolution clock.
|
|
* Either way, the "rating" is set so high that it's always chosen over
|
|
* any other clocksource. */
|
|
if (lguest_data.tsc_khz)
|
|
lguest_clock.mult = clocksource_khz2mult(lguest_data.tsc_khz,
|
|
lguest_clock.shift);
|
|
clock_base = lguest_clock_read();
|
|
clocksource_register(&lguest_clock);
|
|
|
|
/* Now we've set up our clock, we can use it as the scheduler clock */
|
|
pv_time_ops.sched_clock = lguest_sched_clock;
|
|
|
|
/* We can't set cpumask in the initializer: damn C limitations! Set it
|
|
* here and register our timer device. */
|
|
lguest_clockevent.cpumask = cpumask_of_cpu(0);
|
|
clockevents_register_device(&lguest_clockevent);
|
|
|
|
/* Finally, we unblock the timer interrupt. */
|
|
enable_lguest_irq(0);
|
|
}
|
|
|
|
/*
|
|
* Miscellaneous bits and pieces.
|
|
*
|
|
* Here is an oddball collection of functions which the Guest needs for things
|
|
* to work. They're pretty simple.
|
|
*/
|
|
|
|
/* The Guest needs to tell the Host what stack it expects traps to use. For
|
|
* native hardware, this is part of the Task State Segment mentioned above in
|
|
* lguest_load_tr_desc(), but to help hypervisors there's this special call.
|
|
*
|
|
* We tell the Host the segment we want to use (__KERNEL_DS is the kernel data
|
|
* segment), the privilege level (we're privilege level 1, the Host is 0 and
|
|
* will not tolerate us trying to use that), the stack pointer, and the number
|
|
* of pages in the stack. */
|
|
static void lguest_load_esp0(struct tss_struct *tss,
|
|
struct thread_struct *thread)
|
|
{
|
|
lazy_hcall(LHCALL_SET_STACK, __KERNEL_DS|0x1, thread->esp0,
|
|
THREAD_SIZE/PAGE_SIZE);
|
|
}
|
|
|
|
/* Let's just say, I wouldn't do debugging under a Guest. */
|
|
static void lguest_set_debugreg(int regno, unsigned long value)
|
|
{
|
|
/* FIXME: Implement */
|
|
}
|
|
|
|
/* There are times when the kernel wants to make sure that no memory writes are
|
|
* caught in the cache (that they've all reached real hardware devices). This
|
|
* doesn't matter for the Guest which has virtual hardware.
|
|
*
|
|
* On the Pentium 4 and above, cpuid() indicates that the Cache Line Flush
|
|
* (clflush) instruction is available and the kernel uses that. Otherwise, it
|
|
* uses the older "Write Back and Invalidate Cache" (wbinvd) instruction.
|
|
* Unlike clflush, wbinvd can only be run at privilege level 0. So we can
|
|
* ignore clflush, but replace wbinvd.
|
|
*/
|
|
static void lguest_wbinvd(void)
|
|
{
|
|
}
|
|
|
|
/* If the Guest expects to have an Advanced Programmable Interrupt Controller,
|
|
* we play dumb by ignoring writes and returning 0 for reads. So it's no
|
|
* longer Programmable nor Controlling anything, and I don't think 8 lines of
|
|
* code qualifies for Advanced. It will also never interrupt anything. It
|
|
* does, however, allow us to get through the Linux boot code. */
|
|
#ifdef CONFIG_X86_LOCAL_APIC
|
|
static void lguest_apic_write(unsigned long reg, unsigned long v)
|
|
{
|
|
}
|
|
|
|
static unsigned long lguest_apic_read(unsigned long reg)
|
|
{
|
|
return 0;
|
|
}
|
|
#endif
|
|
|
|
/* STOP! Until an interrupt comes in. */
|
|
static void lguest_safe_halt(void)
|
|
{
|
|
hcall(LHCALL_HALT, 0, 0, 0);
|
|
}
|
|
|
|
/* Perhaps CRASH isn't the best name for this hypercall, but we use it to get a
|
|
* message out when we're crashing as well as elegant termination like powering
|
|
* off.
|
|
*
|
|
* Note that the Host always prefers that the Guest speak in physical addresses
|
|
* rather than virtual addresses, so we use __pa() here. */
|
|
static void lguest_power_off(void)
|
|
{
|
|
hcall(LHCALL_CRASH, __pa("Power down"), 0, 0);
|
|
}
|
|
|
|
/*
|
|
* Panicing.
|
|
*
|
|
* Don't. But if you did, this is what happens.
|
|
*/
|
|
static int lguest_panic(struct notifier_block *nb, unsigned long l, void *p)
|
|
{
|
|
hcall(LHCALL_CRASH, __pa(p), 0, 0);
|
|
/* The hcall won't return, but to keep gcc happy, we're "done". */
|
|
return NOTIFY_DONE;
|
|
}
|
|
|
|
static struct notifier_block paniced = {
|
|
.notifier_call = lguest_panic
|
|
};
|
|
|
|
/* Setting up memory is fairly easy. */
|
|
static __init char *lguest_memory_setup(void)
|
|
{
|
|
/* We do this here and not earlier because lockcheck barfs if we do it
|
|
* before start_kernel() */
|
|
atomic_notifier_chain_register(&panic_notifier_list, &paniced);
|
|
|
|
/* The Linux bootloader header contains an "e820" memory map: the
|
|
* Launcher populated the first entry with our memory limit. */
|
|
add_memory_region(boot_params.e820_map[0].addr,
|
|
boot_params.e820_map[0].size,
|
|
boot_params.e820_map[0].type);
|
|
|
|
/* This string is for the boot messages. */
|
|
return "LGUEST";
|
|
}
|
|
|
|
/* We will eventually use the virtio console device to produce console output,
|
|
* but before that is set up we use LHCALL_NOTIFY on normal memory to produce
|
|
* console output. */
|
|
static __init int early_put_chars(u32 vtermno, const char *buf, int count)
|
|
{
|
|
char scratch[17];
|
|
unsigned int len = count;
|
|
|
|
/* We use a nul-terminated string, so we have to make a copy. Icky,
|
|
* huh? */
|
|
if (len > sizeof(scratch) - 1)
|
|
len = sizeof(scratch) - 1;
|
|
scratch[len] = '\0';
|
|
memcpy(scratch, buf, len);
|
|
hcall(LHCALL_NOTIFY, __pa(scratch), 0, 0);
|
|
|
|
/* This routine returns the number of bytes actually written. */
|
|
return len;
|
|
}
|
|
|
|
/*G:050
|
|
* Patching (Powerfully Placating Performance Pedants)
|
|
*
|
|
* We have already seen that pv_ops structures let us replace simple
|
|
* native instructions with calls to the appropriate back end all throughout
|
|
* the kernel. This allows the same kernel to run as a Guest and as a native
|
|
* kernel, but it's slow because of all the indirect branches.
|
|
*
|
|
* Remember that David Wheeler quote about "Any problem in computer science can
|
|
* be solved with another layer of indirection"? The rest of that quote is
|
|
* "... But that usually will create another problem." This is the first of
|
|
* those problems.
|
|
*
|
|
* Our current solution is to allow the paravirt back end to optionally patch
|
|
* over the indirect calls to replace them with something more efficient. We
|
|
* patch the four most commonly called functions: disable interrupts, enable
|
|
* interrupts, restore interrupts and save interrupts. We usually have 6 or 10
|
|
* bytes to patch into: the Guest versions of these operations are small enough
|
|
* that we can fit comfortably.
|
|
*
|
|
* First we need assembly templates of each of the patchable Guest operations,
|
|
* and these are in lguest_asm.S. */
|
|
|
|
/*G:060 We construct a table from the assembler templates: */
|
|
static const struct lguest_insns
|
|
{
|
|
const char *start, *end;
|
|
} lguest_insns[] = {
|
|
[PARAVIRT_PATCH(pv_irq_ops.irq_disable)] = { lgstart_cli, lgend_cli },
|
|
[PARAVIRT_PATCH(pv_irq_ops.irq_enable)] = { lgstart_sti, lgend_sti },
|
|
[PARAVIRT_PATCH(pv_irq_ops.restore_fl)] = { lgstart_popf, lgend_popf },
|
|
[PARAVIRT_PATCH(pv_irq_ops.save_fl)] = { lgstart_pushf, lgend_pushf },
|
|
};
|
|
|
|
/* Now our patch routine is fairly simple (based on the native one in
|
|
* paravirt.c). If we have a replacement, we copy it in and return how much of
|
|
* the available space we used. */
|
|
static unsigned lguest_patch(u8 type, u16 clobber, void *ibuf,
|
|
unsigned long addr, unsigned len)
|
|
{
|
|
unsigned int insn_len;
|
|
|
|
/* Don't do anything special if we don't have a replacement */
|
|
if (type >= ARRAY_SIZE(lguest_insns) || !lguest_insns[type].start)
|
|
return paravirt_patch_default(type, clobber, ibuf, addr, len);
|
|
|
|
insn_len = lguest_insns[type].end - lguest_insns[type].start;
|
|
|
|
/* Similarly if we can't fit replacement (shouldn't happen, but let's
|
|
* be thorough). */
|
|
if (len < insn_len)
|
|
return paravirt_patch_default(type, clobber, ibuf, addr, len);
|
|
|
|
/* Copy in our instructions. */
|
|
memcpy(ibuf, lguest_insns[type].start, insn_len);
|
|
return insn_len;
|
|
}
|
|
|
|
/*G:030 Once we get to lguest_init(), we know we're a Guest. The pv_ops
|
|
* structures in the kernel provide points for (almost) every routine we have
|
|
* to override to avoid privileged instructions. */
|
|
__init void lguest_init(void)
|
|
{
|
|
/* We're under lguest, paravirt is enabled, and we're running at
|
|
* privilege level 1, not 0 as normal. */
|
|
pv_info.name = "lguest";
|
|
pv_info.paravirt_enabled = 1;
|
|
pv_info.kernel_rpl = 1;
|
|
|
|
/* We set up all the lguest overrides for sensitive operations. These
|
|
* are detailed with the operations themselves. */
|
|
|
|
/* interrupt-related operations */
|
|
pv_irq_ops.init_IRQ = lguest_init_IRQ;
|
|
pv_irq_ops.save_fl = save_fl;
|
|
pv_irq_ops.restore_fl = restore_fl;
|
|
pv_irq_ops.irq_disable = irq_disable;
|
|
pv_irq_ops.irq_enable = irq_enable;
|
|
pv_irq_ops.safe_halt = lguest_safe_halt;
|
|
|
|
/* init-time operations */
|
|
pv_init_ops.memory_setup = lguest_memory_setup;
|
|
pv_init_ops.patch = lguest_patch;
|
|
|
|
/* Intercepts of various cpu instructions */
|
|
pv_cpu_ops.load_gdt = lguest_load_gdt;
|
|
pv_cpu_ops.cpuid = lguest_cpuid;
|
|
pv_cpu_ops.load_idt = lguest_load_idt;
|
|
pv_cpu_ops.iret = lguest_iret;
|
|
pv_cpu_ops.load_esp0 = lguest_load_esp0;
|
|
pv_cpu_ops.load_tr_desc = lguest_load_tr_desc;
|
|
pv_cpu_ops.set_ldt = lguest_set_ldt;
|
|
pv_cpu_ops.load_tls = lguest_load_tls;
|
|
pv_cpu_ops.set_debugreg = lguest_set_debugreg;
|
|
pv_cpu_ops.clts = lguest_clts;
|
|
pv_cpu_ops.read_cr0 = lguest_read_cr0;
|
|
pv_cpu_ops.write_cr0 = lguest_write_cr0;
|
|
pv_cpu_ops.read_cr4 = lguest_read_cr4;
|
|
pv_cpu_ops.write_cr4 = lguest_write_cr4;
|
|
pv_cpu_ops.write_gdt_entry = lguest_write_gdt_entry;
|
|
pv_cpu_ops.write_idt_entry = lguest_write_idt_entry;
|
|
pv_cpu_ops.wbinvd = lguest_wbinvd;
|
|
pv_cpu_ops.lazy_mode.enter = paravirt_enter_lazy_cpu;
|
|
pv_cpu_ops.lazy_mode.leave = lguest_leave_lazy_mode;
|
|
|
|
/* pagetable management */
|
|
pv_mmu_ops.write_cr3 = lguest_write_cr3;
|
|
pv_mmu_ops.flush_tlb_user = lguest_flush_tlb_user;
|
|
pv_mmu_ops.flush_tlb_single = lguest_flush_tlb_single;
|
|
pv_mmu_ops.flush_tlb_kernel = lguest_flush_tlb_kernel;
|
|
pv_mmu_ops.set_pte = lguest_set_pte;
|
|
pv_mmu_ops.set_pte_at = lguest_set_pte_at;
|
|
pv_mmu_ops.set_pmd = lguest_set_pmd;
|
|
pv_mmu_ops.read_cr2 = lguest_read_cr2;
|
|
pv_mmu_ops.read_cr3 = lguest_read_cr3;
|
|
pv_mmu_ops.lazy_mode.enter = paravirt_enter_lazy_mmu;
|
|
pv_mmu_ops.lazy_mode.leave = lguest_leave_lazy_mode;
|
|
|
|
#ifdef CONFIG_X86_LOCAL_APIC
|
|
/* apic read/write intercepts */
|
|
pv_apic_ops.apic_write = lguest_apic_write;
|
|
pv_apic_ops.apic_write_atomic = lguest_apic_write;
|
|
pv_apic_ops.apic_read = lguest_apic_read;
|
|
#endif
|
|
|
|
/* time operations */
|
|
pv_time_ops.get_wallclock = lguest_get_wallclock;
|
|
pv_time_ops.time_init = lguest_time_init;
|
|
|
|
/* Now is a good time to look at the implementations of these functions
|
|
* before returning to the rest of lguest_init(). */
|
|
|
|
/*G:070 Now we've seen all the paravirt_ops, we return to
|
|
* lguest_init() where the rest of the fairly chaotic boot setup
|
|
* occurs. */
|
|
|
|
/* The native boot code sets up initial page tables immediately after
|
|
* the kernel itself, and sets init_pg_tables_end so they're not
|
|
* clobbered. The Launcher places our initial pagetables somewhere at
|
|
* the top of our physical memory, so we don't need extra space: set
|
|
* init_pg_tables_end to the end of the kernel. */
|
|
init_pg_tables_end = __pa(pg0);
|
|
|
|
/* Load the %fs segment register (the per-cpu segment register) with
|
|
* the normal data segment to get through booting. */
|
|
asm volatile ("mov %0, %%fs" : : "r" (__KERNEL_DS) : "memory");
|
|
|
|
/* The Host uses the top of the Guest's virtual address space for the
|
|
* Host<->Guest Switcher, and it tells us how big that is in
|
|
* lguest_data.reserve_mem, set up on the LGUEST_INIT hypercall. */
|
|
reserve_top_address(lguest_data.reserve_mem);
|
|
|
|
/* If we don't initialize the lock dependency checker now, it crashes
|
|
* paravirt_disable_iospace. */
|
|
lockdep_init();
|
|
|
|
/* The IDE code spends about 3 seconds probing for disks: if we reserve
|
|
* all the I/O ports up front it can't get them and so doesn't probe.
|
|
* Other device drivers are similar (but less severe). This cuts the
|
|
* kernel boot time on my machine from 4.1 seconds to 0.45 seconds. */
|
|
paravirt_disable_iospace();
|
|
|
|
/* This is messy CPU setup stuff which the native boot code does before
|
|
* start_kernel, so we have to do, too: */
|
|
cpu_detect(&new_cpu_data);
|
|
/* head.S usually sets up the first capability word, so do it here. */
|
|
new_cpu_data.x86_capability[0] = cpuid_edx(1);
|
|
|
|
/* Math is always hard! */
|
|
new_cpu_data.hard_math = 1;
|
|
|
|
#ifdef CONFIG_X86_MCE
|
|
mce_disabled = 1;
|
|
#endif
|
|
#ifdef CONFIG_ACPI
|
|
acpi_disabled = 1;
|
|
acpi_ht = 0;
|
|
#endif
|
|
|
|
/* We set the perferred console to "hvc". This is the "hypervisor
|
|
* virtual console" driver written by the PowerPC people, which we also
|
|
* adapted for lguest's use. */
|
|
add_preferred_console("hvc", 0, NULL);
|
|
|
|
/* Register our very early console. */
|
|
virtio_cons_early_init(early_put_chars);
|
|
|
|
/* Last of all, we set the power management poweroff hook to point to
|
|
* the Guest routine to power off. */
|
|
pm_power_off = lguest_power_off;
|
|
|
|
/* Now we're set up, call start_kernel() in init/main.c and we proceed
|
|
* to boot as normal. It never returns. */
|
|
start_kernel();
|
|
}
|
|
/*
|
|
* This marks the end of stage II of our journey, The Guest.
|
|
*
|
|
* It is now time for us to explore the layer of virtual drivers and complete
|
|
* our understanding of the Guest in "make Drivers".
|
|
*/
|