[PATCH] x86: make X86_BUG_FXSAVE_LEAK detectable in CPUID on AMD

[Rudolf Marek]

The latest AMD AMD64 Architecture Programmer's Manual
adds a CPUID feature XSaveErPtr (CPUID_Fn80000008_EBX[2]).

If this feature is set, the FXSAVE, XSAVE, FXSAVEOPT, XSAVEC, XSAVES
/ FXRSTOR, XRSTOR, XRSTORS always save/restore error pointers,
thus making the X86_BUG_FXSAVE_LEAK workaround obsolete on such CPUs.

Signed-Off-By: Rudolf Marek <r.ma...@assembler.cz>
Reviewed-and-tested-by: Borislav Petkov <b...@suse.de>

---
 arch/x86/include/asm/cpufeatures.h | 1 +
 arch/x86/kernel/cpu/amd.c          | 7 +++++--
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/cpufeatures.h 
b/arch/x86/include/asm/cpufeatures.h
index c0b0e9e..800104c 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -266,6 +266,7 @@
 /* AMD-defined CPU features, CPUID level 0x80000008 (EBX), word 13 */
 #define X86_FEATURE_CLZERO             (13*32+ 0) /* CLZERO instruction */
 #define X86_FEATURE_IRPERF             (13*32+ 1) /* Instructions Retired 
Count */
+#define X86_FEATURE_XSAVEERPTR         (13*32+ 2) /* Always save/restore FP 
error pointers */
 
 /* Thermal and Power Management Leaf, CPUID level 0x00000006 (EAX), word 14 */
 #define X86_FEATURE_DTHERM             (14*32+ 0) /* Digital Thermal Sensor */
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index d58184b..bcb75dc 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -804,8 +804,11 @@ static void init_amd(struct cpuinfo_x86 *c)
        case 0x17: init_amd_zn(c); break;
        }
 
-       /* Enable workaround for FXSAVE leak */
-       if (c->x86 >= 6)
+       /*
+        * Enable workaround for FXSAVE leak on CPUs
+        * without a XSaveErPtr feature
+        */
+       if ((c->x86 >= 6) && (!cpu_has(c, X86_FEATURE_XSAVEERPTR)))
                set_cpu_bug(c, X86_BUG_FXSAVE_LEAK);
 
        cpu_detect_cache_sizes(c);
-- 
2.7.4