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

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Date:	Mon, 3 Mar 2008 18:53:28 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Pavel Machek <pavel@....cz>,
	"Klaus S. Madsen" <ksm@...rnemadsen.org>,
	Suspend-devel list <suspend-devel@...ts.sourceforge.net>,
	LKML <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Regression in 2.6.25-rc3: s2ram segfaults before suspending


* H. Peter Anvin <hpa@...or.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@...p.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@...e.hu>
 Date:   Wed Jan 30 13:32:55 2008 +0100

     x86/pgtable: fix constant sign extension problem

 commit dcbae6b377d78190954055ef2d8909ae83ff57de
 Author: Ingo Molnar <mingo@...e.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@...e.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@...e.hu>
    Signed-off-by: Thomas Gleixner <tglx@...utronix.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 \
--
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