x86/cpu: Add Erratum 88 detection on AMD

Erratum 88 affects old AMD K8s, where a SWAPGS fails to cause an input
dependency on GS. Therefore, we need to MFENCE before it.

But that MFENCE is expensive and unnecessary on the remaining x86 CPUs
out there so patch it out on the CPUs which don't require it.

Signed-off-by: Borislav Petkov <[email protected]>
Signed-off-by: Andy Lutomirski <[email protected]
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Rudolf Marek <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/aec6b2df1bfc56101d4e9e2e5d5d570bf41663c6.1460075211.git.luto@kernel.org
Signed-off-by: Ingo Molnar <[email protected]>

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 858b555e274b8d763d97d9b9cf14998125bce563..64d2033d1e49d5bc3d65c05d83d86c6a339ddec1 100644 (file)
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -783,7 +783,7 @@ ENTRY(native_load_gs_index)
        SWAPGS
 gs_change:
        movl    %edi, %gs
-2:     mfence                                  /* workaround */
+2:     ALTERNATIVE "", "mfence", X86_BUG_SWAPGS_FENCE
        SWAPGS
        popfq
        ret

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 2a052302bc4397286bcb042eaf105e175ffe14b5..7bfb6b70c7452831dd5c7b88c440fe44267d52da 100644 (file)
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -295,6 +295,8 @@
 #define X86_BUG_CLFLUSH_MONITOR        X86_BUG(7) /* AAI65, CLFLUSH required before MONITOR */
 #define X86_BUG_SYSRET_SS_ATTRS        X86_BUG(8) /* SYSRET doesn't fix up SS attrs */
 #define X86_BUG_NULL_SEG       X86_BUG(9) /* Nulling a selector preserves the base */
+#define X86_BUG_SWAPGS_FENCE   X86_BUG(10) /* SWAPGS without input dep on GS */
+
 
 #ifdef CONFIG_X86_32
 /*

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 6e47e3a916f12a03069a7c38ef21e9b2df5edcdf..b7cc9efe08b5c92204a8401082b56281223c77ba 100644 (file)
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -632,6 +632,7 @@ static void init_amd_k8(struct cpuinfo_x86 *c)
         */
        msr_set_bit(MSR_K7_HWCR, 6);
 #endif
+       set_cpu_bug(c, X86_BUG_SWAPGS_FENCE);
 }
 
 static void init_amd_gh(struct cpuinfo_x86 *c)