Patch "x86: Make X86_BUG_FXSAVE_LEAK detectable in CPUID on AMD" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

x86: Make X86_BUG_FXSAVE_LEAK detectable in CPUID on AMD

to the 4.14-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-make-x86_bug_fxsave_leak-detectable-in-cpuid-on-amd.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Rudolf Marek <[email protected]>
Date: Tue, 28 Nov 2017 22:01:06 +0100
Subject: x86: Make X86_BUG_FXSAVE_LEAK detectable in CPUID on AMD

From: Rudolf Marek <[email protected]>

commit f2dbad36c55e5d3a91dccbde6e8cae345fe5632f upstream.

[ Note, this is a Git cherry-pick of the following commit:

    2b67799bdf25 ("x86: Make X86_BUG_FXSAVE_LEAK detectable in CPUID on AMD")

... for easier x86 PTI code testing and back-porting. ]

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.

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

@@ -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 */

@@ -804,8 +804,11 @@ static void init_amd(struct cpuinfo_x86
 	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);

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/x86-make-x86_bug_fxsave_leak-detectable-in-cpuid-on-amd.patch