linux-kernel - Re: [git pull] x86 fixes

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Date:	Thu, 27 Mar 2008 21:50:12 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [git pull] x86 fixes


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> >  #ifdef CONFIG_X86_32
> > -	if (!(__supported_pte_mask & _PAGE_NX))
> > +	/* Catch an obscure case of prefetch inside an NX page: */
> > +	if ((__supported_pte_mask & _PAGE_NX) && (error_code & 16))
> >  		return 0;
> >  #endif
> 
> Ingo, this patch makes no sense.
> 
> Two reasons:
> 
>  - "error_code & 16" is senseless. Use PF_INSTR instead, which actually 
>    tells the reader something.

yeah - sorry - the '16' was a blast from the past, i just took the old 
2.6.24 condition on the 32-bit side which didnt use PF_INSTR (PF_INSTR 
came in as a cleanup during the unification), and when the confirmation 
came that this fixed the crash i sent the pull request. That's how this 
nonsensical mixing happened, and that's why i missed the 'if (error_code 
& PF_INSTR)' branch.

The patch below (ontop of the tree) is a first cut at fixing all these 
problems - but i'd wait at least 24 hours with applying this to let it 
be tested through - it affects both 32-bit and 64-bit. The fix further 
cleans up this codepath and removes an #ifdef.

	Ingo

------------------------>
Subject: x86: prefetch fix #2
From: Ingo Molnar <mingo@...e.hu>
Date: Thu Mar 27 21:29:09 CET 2008

Linus noticed a second bug and an uncleanliness:

 - we'd return on any instruction fetch fault

 - we'd use both the value of 16 and the PF_INSTR symbol which are
   the same and make no sense

the cleanup nicely unifies this piece of logic.

Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 arch/x86/mm/fault.c |   12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

Index: linux-x86.q/arch/x86/mm/fault.c
===================================================================
--- linux-x86.q.orig/arch/x86/mm/fault.c
+++ linux-x86.q/arch/x86/mm/fault.c
@@ -103,14 +103,10 @@ static int is_prefetch(struct pt_regs *r
 	int prefetch = 0;
 	unsigned char *max_instr;
 
-#ifdef CONFIG_X86_32
-	/* Catch an obscure case of prefetch inside an NX page: */
-	if ((__supported_pte_mask & _PAGE_NX) && (error_code & 16))
-		return 0;
-#endif
-
-	/* If it was a exec fault on NX page, ignore */
-	if (error_code & PF_INSTR)
+	/*
+	 * Catch an obscure case of prefetch inside an NX page:
+	 */
+	if ((__supported_pte_mask & _PAGE_NX) && (error_code & PF_INSTR))
 		return 0;
 
 	instr = (unsigned char *)convert_ip_to_linear(current, regs);
--
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