linux-kernel - Re: [git head] X86

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Message-ID: <21d7e9970805092319n1d31be36h2f2c7d46622f46c8@mail.gmail.com>
Date:	Sat, 10 May 2008 16:19:27 +1000
From:	"Dave Airlie" <airlied@...il.com>
To:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>, "Hugh Dickins" <hugh@...itas.com>,
	"Frans Pop" <elendil@...net.nl>,
	"Barnes, Jesse" <jesse.barnes@...el.com>,
	linux-kernel@...r.kernel.org,
	"Packard, Keith" <keith.packard@...el.com>,
	"Yinghai Lu" <yhlu.kernel@...il.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Nick Piggin" <npiggin@...e.de>,
	"Jesse Barnes" <jbarnes@...tuousgeek.org>
Subject: Re: [git head] X86_PAT & mprotect

On Sat, May 10, 2008 at 8:20 AM, Pallipadi, Venkatesh
<venkatesh.pallipadi@...el.com> wrote:
>
>
>
>  >-----Original Message-----
>  >From: Dave Airlie [mailto:airlied@...il.com]
>  >Sent: Friday, May 09, 2008 3:11 PM
>  >To: Pallipadi, Venkatesh
>  >Cc: Ingo Molnar; Hugh Dickins; Frans Pop; Barnes, Jesse;
>  >linux-kernel@...r.kernel.org; Packard, Keith; Yinghai Lu;
>  >Andrew Morton; Linus Torvalds; H. Peter Anvin; Thomas
>  >Gleixner; Nick Piggin; Jesse Barnes
>  >Subject: Re: [git head] X86_PAT & mprotect
>  >
>  >On Sat, May 10, 2008 at 6:05 AM, Venki Pallipadi
>  ><venkatesh.pallipadi@...el.com> wrote:
>  >> On Fri, May 09, 2008 at 12:08:18PM +0200, Ingo Molnar wrote:
>  >>  >
>  >>  > * Venki Pallipadi <venkatesh.pallipadi@...el.com> wrote:
>  >>  >
>  >>  > > > I've tried doing it slightly differently below, don't
>  >know whether
>  >>  > > > you'll consider it an improvement or not.
>  >>  > >
>  >>  > > Hugh: Thanks for looking into this. Yes. I like your
>  >modified patch.
>  >>  > > Simpler and smaller.
>  >>  >
>  >>  > i have stuck your original patch into testing and nothing
>  >blew up so
>  >>  > far. Due to the mm/ bits this is not for the scope of x86.git, but
>  >>  > obviously it all looks good and is .26-worthy to me:
>  >>  >
>  >>  >  Acked-by: Ingo Molnar <mingo@...e.hu>
>  >>  >  Tested-by: Ingo Molnar <mingo@...e.hu>
>  >>  >
>  >>  > Venki, could you please send a full patch against -git that has
>  >>  > everything from Hugh included, with an updated changelog, for
>  >>  > Linus/Andrew to ack/apply?
>  >>  >
>  >>
>  >>  Ingo,
>  >>
>  >>  Split up the patch into two parts as the pci part was
>  >unrelated to mprotect
>  >>  problem in a sense.
>  >>
>  >>  Here is the first patch.
>  >>
>  >>  Thanks,
>  >>  Venki
>  >>
>  >>
>  >>  Some versions of X used the mprotect workaround to change
>  >caching type from
>  >>
>  >> UC to WB, so that it can then use mtrr to program WC for
>  >that region [1].
>  >>  Change the mmap of pci space through /sys or /proc
>  >interfaces from UC to
>  >>  UC_MINUS. With this change, X will not need to use mprotect
>  >>  workaround to get WC type.
>  >>  Also the bug with mprotect which lets caller to change PAT
>  >bits is fixed in
>  >>  the follow on patch. So, this X workaround will stop
>  >working as well.
>  >>
>  >
>  >Wow this kinda puts X in a nasty position, we have 2.6.25 and
>  >previous kernels
>  >where we use the original /sys interfaces and nasty hack to
>  >workaround, but on 2.6.26 we magically need to
>  >switch to the /sys _uc interfaces or the users X will slow down.
>  >
>
>  No. With 2.6.26 you can still use same /sys resource file, without
>  the mprotect workaround and set the MTRR as before.
>
>  The change from UC to UC_MINUS in this patch ensures that the
>  X drivers MTRR will take precedence and X does not need any mprotect
>  hacks.
>

Cool just making sure.

Keithp, I hope we didn't error check the mremap return values :)

Dave.
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