linux-kernel - [PATCH 0/3] ACPI SRAT: Disregard reserved PXM bits

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Date:	Sun, 15 Jan 2012 22:30:05 +0100
From:	Kurt Garloff <kurt@...loff.de>
To:	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org
Cc:	stable@...r.kernel.org, Len Brown <lenb@...nel.org>
Subject: [PATCH 0/3] ACPI SRAT: Disregard reserved PXM bits

Hi,

this has been submitted thrice already -- and while it found a bit of
friendly feedback, it has not been merged. It should be IMVHO, and I
hope this time the right eyes see this flying by ...
I should mention that it fixes a real problem (wrong affinities reported
in sysfs and thus userspace high-perf compute code taking wrong
decisions) and that this has been part of SUSE enterprise kernels since 
a few years now.
It should also go right into stable IMVHO.

Original description to follow ...

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, v1 only 8 bits.)
This can lead to problems with poor BIOS implementations that failed
to set reserved 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 was 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 is against current git.

Note: If you respond to this mail, please keep me in Cc -- I'm not
subscribed to LKML these days.

Cheers,
-- 
Kurt Garloff <kurt@...loff.de>  [Koeln/Greven]

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