Example memory map (HP rx7640 with 'default' acpiconfig setting, VGA disabled):
0x00000000 - 0x3FFFBFFF supports only WB (cacheable) access
If a user attempts to perform an MMIO mmap (using the PCIIOC_MMAP_IS_MEM ioctl)
to PCI config space (like mmap'ing and accessing memory at 0xA0000),
we will MCA because the kernel will attempt to use a mapping with the UC
attribute.
So check the memory attribute in kern_mmap and the EFI memmap. If WC is
requested, and WC or UC access is supported for the region, allow it.
Otherwise, use the same attribute the kernel uses.
Updates documentation and test cases as well.
Signed-off-by: Alex Chiang <achiang@hp.com>
Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
This closes a couple holes in our attribute aliasing avoidance scheme:
- The current kernel fails mmaps of some /dev/mem MMIO regions because
they don't appear in the EFI memory map. This keeps X from working
on the Intel Tiger box.
- The current kernel allows UC mmap of the 0-1MB region of
/sys/.../legacy_mem even when the chipset doesn't support UC
access. This causes an MCA when starting X on HP rx7620 and rx8620
boxes in the default configuration.
There's more detail in the Documentation/ia64/aliasing.txt file this
adds, but the general idea is that if a region might be covered by
a granule-sized kernel identity mapping, any access via /dev/mem or
mmap must use the same attribute as the identity mapping.
Otherwise, we fall back to using an attribute that is supported
according to the EFI memory map, or to using UC if the EFI memory
map doesn't mention the region.
Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
