Re: [PATCH] x86/PCI: never allocate PCI space from the last 1M below 4G

[Bjorn Helgaas <bjorn.helgaas@hp.com>]

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@redhat.com>
> Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
> ---
> 
>  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.

Bjorn