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    SubjectRe: Regression in 2.6.25-rc3: s2ram segfaults before suspending
    On Mon 2008-03-03 22:05:26, Pavel Machek wrote:
    > Hi!
    >
    > > However I wasn't able to make the problem go away, by removing the
    > > _PAGE_PWT constants from __PAGE_KERNEL_NOCACHE and
    > > __PAGE_KERNEL_VSYSCALL_NOCACHE in include-asm/pgtable.h in the newest
    > > 2.6.25:
    > >
    > > diff --git a/include/asm-x86/pgtable.h b/include/asm-x86/pgtable.h
    > > index 174b877..f81c968 100644
    > > --- a/include/asm-x86/pgtable.h
    > > +++ b/include/asm-x86/pgtable.h
    > > @@ -84,9 +84,9 @@ extern pteval_t __PAGE_KERNEL, __PAGE_KERNEL_EXEC;
    > > #define __PAGE_KERNEL_RO (__PAGE_KERNEL & ~_PAGE_RW)
    > > #define __PAGE_KERNEL_RX (__PAGE_KERNEL_EXEC & ~_PAGE_RW)
    > > #define __PAGE_KERNEL_EXEC_NOCACHE (__PAGE_KERNEL_EXEC | _PAGE_PCD | _PAGE_PWT)
    > > -#define __PAGE_KERNEL_NOCACHE (__PAGE_KERNEL | _PAGE_PCD | _PAGE_PWT)
    > > +#define __PAGE_KERNEL_NOCACHE (__PAGE_KERNEL | _PAGE_PCD)
    > > #define __PAGE_KERNEL_VSYSCALL (__PAGE_KERNEL_RX | _PAGE_USER)
    > > -#define __PAGE_KERNEL_VSYSCALL_NOCACHE (__PAGE_KERNEL_VSYSCALL | _PAGE_PCD | _PAGE_PWT)
    > > +#define __PAGE_KERNEL_VSYSCALL_NOCACHE (__PAGE_KERNEL_VSYSCALL | _PAGE_PCD)
    > > #define __PAGE_KERNEL_LARGE (__PAGE_KERNEL | _PAGE_PSE)
    > > #define __PAGE_KERNEL_LARGE_EXEC (__PAGE_KERNEL_EXEC | _PAGE_PSE)
    > >
    > > So while I'm fairly confident in that I bisected correctly, the number
    > > of attempts I had to go through to get a reliable result, and the fact
    > > that I cannot make the problem go away by reverting the current code to
    > > something similar, counts quite a lot against me.
    > >
    > > However I'm 100% confident that the problem appears between
    > > cf8fa920cb4271f17e0265c863d64bea1b31941a and
    > > 925596a017bbd045ff711b778256f459e50a119, which is something like 16
    > > commits. I have been at both points in the tree at least 2 times, and
    > > confirmed that cf8fa920cb4271f17e0265c863d64bea1b31941a worked for me,
    > > and 925596a017bbd045ff711b778256f459e50a119 didn't.
    > >
    > > > while requiring PROT_EXEC is fine, breaking existing user-space apps
    > > > over that is not fine. So are you absolutely sure that by reverting that
    > > > PWT|PCD commit, s2ram again starts to work? That's utmost weird...
    > > I'm sure that it fixed the problem for me, yes, and I'm fairly confident
    > > that I ran make clean && make to compile the kernel during the entire
    > > bisection between the two commites mentioned above.
    > >
    > > > perhaps there's some CPU bug that causes NX to _NOT_ work if only PCD is
    > > > used (not PCD|PWT). Seems like a pretty unlikely scenario though.
    > > $ cat /proc/cpuinfo
    > > processor : 0
    > > vendor_id : GenuineIntel
    > > cpu family : 6
    > > model : 15
    > > model name : Intel(R) Core(TM)2 Duo CPU T7500 @ 2.20GHz
    > > stepping : 10
    > >
    > > But I'm a bit puzzled by the fact that I'm aparently the only one how
    > > have encountered the problem? Maybe it's only a problem if one also uses
    > > PAE? (Thats just a wild guess to explain why I'm the only one seeing
    > > this).
    >
    > I do not have NX capable CPU in machine using for suspend
    > testing. ... and you are using 32-bit userspace on 64-bit kernel,
    > right?

    Sorry, I meant "32-bit userspace on 32-bit kernel"... but that on
    64-bit capable cpu.
    Pavel
    --
    (english) http://www.livejournal.com/~pavelmachek
    (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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