linux-kernel - Re: [PATCH 0/3]: Discard reserved PXM bits for SRAT v1

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Date:	Tue, 19 May 2009 11:01:50 +0200
From:	xb <xavier.bru@...l.net>
To:	Kurt Garloff <garloff@...e.de>,
	Linux kernel list <linux-kernel@...r.kernel.org>,
	Norbert Eicker <N.Eicker@...juelich.de>,
	Greg Kroah-Hartman <GregKH@...e.de>,
	Alexey Starikovskiy <AStarikovskiy@...e.cz>,
	Len Brown <LenB@...nel.org>
Subject: Re: [PATCH 0/3]: Discard reserved PXM bits for SRAT v1

Hi Kurt,

We are hitting this problem on some Nehalem based platforms, that 
prevents a correct Numa initialization.
We propsed a patch on linux_acpi to fix it.
We are OK to have your patch go into the mainstream to have this fixed 
quickly.
Thanks.
Xavier

Kurt Garloff wrote:
> Hi,
>
> ACPI specification says that the OS must disregard reserved bits.
> The x86_64 SRAT parser does not discard the upper 24 bits of the
> proximity_domain (pxm) in the acpi_srat_mem_affinity entries for
> SRAT v1 tables. (v2 has 32 bits wide fields.)
> This can lead to problems with poor BIOS implementations that failed
> to set resreved bytes to zero. (The ACPI spec is a bit vague here
> unfortunately.)
>
> This was also inconsistent: On x86-64 (srat_64.c), the 
> _cpu_affinity does only use the low 8 bits of pxm, while the
> full 32 bits of _mem_affinity are consumed.
> In srat_32.c (x86), only 8bits are used (which is OK, a 32bit system
> with >256 PXMs does not seem reasonable at all).
> On ia64, the support of more than 8 bits was consistent between
> mem and cpu affinity entries, however it dependent on "sn2" platform.
>
> The patch series has the following goals:
> * Make the kernel support consistently 8bits or 32bits for the
>   proximity domain
> * Make this dependent on the SRAT version; v1 => 8bits, v2 => 32bits.
>
> Overview over the patches:
> - [1/3] Store the SRAT table version value in acpi_srat_revision 
> - [2/3] x86-64: Discard the upper 24 bits in mem_affinity if rev <= 1
>         and use upper 24bits in cpu_affinity if rev >= 2
> - [3/3] ia64: Also use upper 8/24bits if rev >= 2 (but leave logic to
>         enable on sn2 as well -- I don't know if sn2 reports v1 or v2
>         SRAT) Also add two __init decls in ia64 pxm accessors.
>
> Patch has been tested on x86-64 against an 2.6.27.x kernel.
> (Patch is against current git.)
>
> Thanks for James, Greg, Alexey, Norbert for comments, review and testing.
>
> Please review and apply!
>
> Greg, I believe this is a candidate for -stable.
>   
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