3.5.7.19 -stable review patch. If anyone has any objections, please let me know.
------------------
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 doesn’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: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
arch/x86/kernel/i387.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index f250431..6c5a7dc 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -132,7 +132,7 @@ static void __cpuinit mxcsr_feature_mask_init(void)
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;
--
1.8.3.2
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