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    SubjectRe: Regression in 2.6.25-rc3: s2ram segfaults before suspending
    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?

    Pavel
    --
    (english) http://www.livejournal.com/~pavelmachek
    (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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