Example memory map (from HP sx1000 with VGA enabled):
0x00000 - 0x9FFFF supports only WB (cacheable) access
0xA0000 - 0xBFFFF supports only UC (uncacheable) access
0xC0000 - 0xFFFFF supports only WB (cacheable) access
pci_read_rom() indirectly uses ioremap(0xC0000) to read the shadow VGA option
ROM. ioremap() used to default to a 16MB or 64MB UC kernel identity mapping,
which would cause an MCA when reading 0xC0000 since only WB is supported there.
X uses reads the option ROM to initialize devices. A smaller test case is:
# echo 1 > /sys/bus/pci/devices/0000:aa:03.0/rom
# cp /sys/bus/pci/devices/0000:aa:03.0/rom x
To avoid this, we can use the same ioremap_page_range() strategy that most
architectures use for all ioremaps. These page table mappings come out of the
vmalloc area. On ia64, these are in region 5 (0xA... addresses) and typically
use 16KB or 64KB mappings instead of 16MB or 64MB mappings. The smaller
mappings give more flexibility to use the correct attributes.
Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
9b50ffb0c0