Messages in this thread | | | Subject | RE: [git head] X86_PAT & mprotect | Date | Fri, 9 May 2008 15:20:08 -0700 | From | "Pallipadi, Venkatesh" <> |
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>-----Original Message----- >From: Dave Airlie [mailto:airlied@gmail.com] >Sent: Friday, May 09, 2008 3:11 PM >To: Pallipadi, Venkatesh >Cc: Ingo Molnar; Hugh Dickins; Frans Pop; Barnes, Jesse; >linux-kernel@vger.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@intel.com> wrote: >> On Fri, May 09, 2008 at 12:08:18PM +0200, Ingo Molnar wrote: >> > >> > * Venki Pallipadi <venkatesh.pallipadi@intel.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@elte.hu> >> > Tested-by: Ingo Molnar <mingo@elte.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.
Thanks, Venki
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