On 11/29/2010 12:34 PM, Bjorn Helgaas wrote: > On Monday, November 29, 2010 11:30:09 am Bjorn Helgaas wrote: >> >> The last 1M before 4G contains the processor restart vector and usually >> the system ROM. We don't know the actual ROM size; I chose 1M because >> that's how much Windows 7 appears to avoid. >> >> Without this check, we can allocate PCI space that will never work. On >> Matthew's HP 2530p, we put the Intel GTT "Flush Page" at the very last >> page, which causes a spontaneous power-off: >> >> pci_root PNP0A08:00: host bridge window [mem 0xfee01000-0xffffffff] >> fffff000-ffffffff : Intel Flush Page (assigned by intel-gtt) >> >> Reference: https://bugzilla.kernel.org/show_bug.cgi?id=23542 >> Reported-by: Matthew Garrett <mjg@xxxxxxxxxx> >> Signed-off-by: Bjorn Helgaas <bjorn.helgaas@xxxxxx> >> --- >> >> arch/x86/include/asm/e820.h | 3 +++ >> arch/x86/pci/i386.c | 10 +++++++++- >> 2 files changed, 12 insertions(+), 1 deletions(-) >> >> >> diff --git a/arch/x86/include/asm/e820.h b/arch/x86/include/asm/e820.h >> index 5be1542..c1e908f 100644 >> --- a/arch/x86/include/asm/e820.h >> +++ b/arch/x86/include/asm/e820.h >> @@ -72,6 +72,9 @@ struct e820map { >> #define BIOS_BEGIN 0x000a0000 >> #define BIOS_END 0x00100000 >> >> +#define BIOS_ROM_BASE 0xfff00000 >> +#define BIOS_ROM_END 0x100000000ULL > > I'm really not thrilled about hard-coding these addresses, so I'd > love it if somebody could suggest a way to discover them from the > BIOS. > > The E820 map doesn't reserve the last page: > > BIOS-e820: 00000000fed1c000 - 00000000fed20000 (reserved) > BIOS-e820: 00000000fffa0000 - 00000000fffa7000 (reserved) > > and I don't think there's any ACPI device that does either. > It is certainly reasonable to block off the last chunk of the 32-bit address space. Some systems double-decode it to avoid issues with A20M#, so I would argue that we should avoid at least 2 MiB. As far as discovering them from the BIOS, there is a way to do it -- E820. This is a fallback for the case where the BIOS has plain and simply failed to provide it, and so a heuristic is probably the best we can do. Probing is extremely unsafe. -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
