Re: [git pull] x86 fixes

Ingo Molnar
2008-03-27T21:01:55Z

* Ingo Molnar <mingo@elte.hu> wrote:

> i suspect we would be fine with a simple:
>
> if (error_code & PF_INSTR)
> return 0;
>
> because if we get a fault on an instruction fetch then it clearly
> cannot be a prefetch erratum ... The NX condition simply comes from a
> cautious 32-bit workaround. (on 64-bit we always have NX - at least on
> AMD which has this erratum.)
>
> and thus the currently pulled code is not incorrect, just ugly and
> nonsensical.

i.e. the patch below, which is even simpler. The comments were a bit
confusing as well - in this function we decide whether to ignore a
fault, so returning 0 means we do _not_ ignore a fault (but process it
to the bitter end most likely).

Ingo

-------------->
Subject: x86: prefetch fix #2
From: Ingo Molnar <mingo@elte.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@elte.hu>
---
arch/x86/mm/fault.c | 11 ++++-------
1 file changed, 4 insertions(+), 7 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
@@ -103,13 +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 it was a exec (instruction fetch) fault on NX page, then
+ * do not ignore the fault:
+ */
if (error_code & PF_INSTR)
return 0;