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Date:	Mon, 26 Oct 2009 14:12:52 -0700
From:	Jesse Barnes <>
To:	Suresh Siddha <>
Cc:	Ingo Molnar <>,
	Thomas Schlichter <>,
	LKML <>,
	Eric Anholt <>,
	Thomas Hellstrom <>,
	Jan Beulich <>
Subject: Re: [patch] x86, pat: return EINVAL for pci mmap WC request for

On Mon, 26 Oct 2009 13:21:32 -0800
Suresh Siddha <> wrote:

> Thomas Schlichter reported:
> > uses libpciaccess which tries to mmap with write combining
> > enabled via /sys/bus/pci/devices/*/resource0_wc. Currently, when
> > PAT is not enabled, the kernel does fall back to uncached mmap.
> > Then libpciaccess thinks it succeeded mapping with write combining
> > enabled and does not set up suited MTRR entries. ;-(
> Instead of silently mapping pci mmap region as UC minus in the case
> of !pat_enabled and wc request, we can return error. Eric Anholt
> mentioned that caller (like X) typically follows up with UC minus pci
> mmap request and if there is a free mtrr slot, caller will manage
> adding WC mtrr.
> Jesse Barnes says:
> > Older versions of libpciaccess will behave better if we do it that
> > way (iirc it only allocates an MTRR if the resource_wc file doesn't
> > exist or fails to get mapped).
> Reported-by: Thomas Schlichter <>
> Signed-off-by: Thomas Schlichter <>
> Signed-off-by: Suresh Siddha <>
> Acked-by: Eric Anholt <>
> Acked-by: Jesse Barnes <>
> ---

Applied to my linux-next branch, thanks.

Jesse Barnes, Intel Open Source Technology Center
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