This is a note to let you know that I've just added the patch titled
x86, fpu: correct the asm constraints for fxsave, unbreak mxcsr.daz
to the 3.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-fpu-correct-the-asm-constraints-for-fxsave-unbreak-mxcsr.daz.patch
and it can be found in the queue-3.0 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From eaa5a990191d204ba0f9d35dbe5505ec2cdd1460 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@xxxxxxxxx>
Date: Fri, 26 Jul 2013 09:11:56 -0700
Subject: x86, fpu: correct the asm constraints for fxsave, unbreak mxcsr.daz
From: "H.J. Lu" <hjl.tools@xxxxxxxxx>
commit eaa5a990191d204ba0f9d35dbe5505ec2cdd1460 upstream.
GCC will optimize mxcsr_feature_mask_init in arch/x86/kernel/i387.c:
memset(&fx_scratch, 0, sizeof(struct i387_fxsave_struct));
asm volatile("fxsave %0" : : "m" (fx_scratch));
mask = fx_scratch.mxcsr_mask;
if (mask == 0)
mask = 0x0000ffbf;
to
memset(&fx_scratch, 0, sizeof(struct i387_fxsave_struct));
asm volatile("fxsave %0" : : "m" (fx_scratch));
mask = 0x0000ffbf;
since asm statement doesnâ??t say it will update fx_scratch. As the
result, the DAZ bit will be cleared. This patch fixes it. This bug
dates back to at least kernel 2.6.12.
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/i387.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -51,7 +51,7 @@ void __cpuinit mxcsr_feature_mask_init(v
clts();
if (cpu_has_fxsr) {
memset(&fx_scratch, 0, sizeof(struct i387_fxsave_struct));
- asm volatile("fxsave %0" : : "m" (fx_scratch));
+ asm volatile("fxsave %0" : "+m" (fx_scratch));
mask = fx_scratch.mxcsr_mask;
if (mask == 0)
mask = 0x0000ffbf;
Patches currently in stable-queue which might be from hjl.tools@xxxxxxxxx are
queue-3.0/x86-fpu-correct-the-asm-constraints-for-fxsave-unbreak-mxcsr.daz.patch
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