Re: Regression in 2.6.25-rc3: s2ram segfaults before suspending

Ingo Molnar
2008-03-03T17:54:12Z

* H. Peter Anvin <hpa@zytor.com> wrote:

>> It is strange indeed... Should it be traced as an regression?
>
> I'd like to understand what the heck happened, but as far as we can
> observe right now, it's a *progression*, not a regression, since
> executing out of a non-PROT_EXEC area isn't *supposed* to work...

if s2ram worked before, and breaks with v2.6.25 then it's a regression.
It doesnt really matter that this segfault is the right thing to do ...

what would be _really_ nice to know how this all links up to the PCD ->
PCD|PWT commit. I.e. how did the commit below suddenly _trigger_ this
segfault? Are we absolutely sure that the bisection is correct, that
it's this commit which broke things? [i.e. if this commit is unapplied,
does s2ram work?]

there are a few "nearby" commits in the bisection tree:

commit 6c3866558213ff706d8331053386915371ad63ec
Author: Jeremy Fitzhardinge <jeremy@goop.org>
Date: Wed Jan 30 13:32:55 2008 +0100

x86: move all asm/pgtable constants into one place

commit 61f38226def55d972cfd0e789971e952525ff8e5
Author: Ingo Molnar <mingo@elte.hu>
Date: Wed Jan 30 13:32:55 2008 +0100

x86/pgtable: fix constant sign extension problem

commit dcbae6b377d78190954055ef2d8909ae83ff57de
Author: Ingo Molnar <mingo@elte.hu>
Date: Wed Jan 30 13:32:55 2008 +0100

x86/pgtable: unify pagetable accessors, #1

which are far more likely candidates IMO of causing this NX related
segfault than the PCD->PCD|PWT change that was bisected originally.

Ingo

---------->
commit 82bc03fc158e28c90d7ed9919410776039cb4e14
Author: Ingo Molnar <mingo@elte.hu>
Date: Wed Jan 30 13:32:54 2008 +0100

x86: add PWT to NOCACHE flags

add PWT bit to NOCACHE flags. No real difference to CPUs, but needed
later for PAT.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/include/asm-x86/pgtable_32.h b/include/asm-x86/pgtable_32.h
index a8be1ee..16da5d5 100644
--- a/include/asm-x86/pgtable_32.h
+++ b/include/asm-x86/pgtable_32.h
@@ -156,7 +156,7 @@ void paging_init(void);
extern unsigned long long __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_NOCACHE (__PAGE_KERNEL | _PAGE_PCD)
+#define __PAGE_KERNEL_NOCACHE (__PAGE_KERNEL | _PAGE_PCD | _PAGE_PWT)
#define __PAGE_KERNEL_LARGE (__PAGE_KERNEL | _PAGE_PSE)
#define __PAGE_KERNEL_LARGE_EXEC (__PAGE_KERNEL_EXEC | _PAGE_PSE)

diff --git a/include/asm-x86/pgtable_64.h b/include/asm-x86/pgtable_64.h
index 3f28010..9c9cddf 100644
--- a/include/asm-x86/pgtable_64.h
+++ b/include/asm-x86/pgtable_64.h
@@ -189,13 +189,13 @@ static inline pte_t ptep_get_and_clear_full(struct mm_struct *mm, unsigned long
#define __PAGE_KERNEL_EXEC \
(_PAGE_PRESENT | _PAGE_RW | _PAGE_DIRTY | _PAGE_ACCESSED)
#define __PAGE_KERNEL_NOCACHE \
- (_PAGE_PRESENT | _PAGE_RW | _PAGE_DIRTY | _PAGE_PCD | _PAGE_ACCESSED | _PAGE_NX)
+ (_PAGE_PRESENT | _PAGE_RW | _PAGE_DIRTY | _PAGE_PCD | _PAGE_PWT | _PAGE_ACCESSED | _PAGE_NX)
#define __PAGE_KERNEL_RO \
(_PAGE_PRESENT | _PAGE_DIRTY | _PAGE_ACCESSED | _PAGE_NX)
#define __PAGE_KERNEL_VSYSCALL \
(_PAGE_PRESENT | _PAGE_USER | _PAGE_ACCESSED)
#define __PAGE_KERNEL_VSYSCALL_NOCACHE \
- (_PAGE_PRESENT | _PAGE_USER | _PAGE_ACCESSED | _PAGE_PCD)
+ (_PAGE_PRESENT | _PAGE_USER | _PAGE_ACCESSED | _PAGE_PCD | _PAGE_PWT)
#define __PAGE_KERNEL_LARGE \
(__PAGE_KERNEL | _PAGE_PSE)
#define __PAGE_KERNEL_LARGE_EXEC \