x86: Make X86_BUG_FXSAVE_LEAK detectable in CPUID on AMD

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 <[email protected]> Signed-off-by: Thomas Gleixner <[email protected]> Reviewed-by: Borislav Petkov <[email protected]> Tested-by: Borislav Petkov <[email protected]> Cc: Andy Lutomirski <[email protected]> Link: https://lkml.kernel.org/r/[email protected]
torvalds · Nov 29, 2017 · 2b67799 · 2b67799
1 parent 55d2d0a
commit 2b67799
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Showing 2 changed files with 6 additions and 2 deletions.
diff --git 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
@@ -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);