[PATCH 3.16 65/86] x86/kvm: Expose X86_FEATURE_MD_CLEAR to guests

[Ben Hutchings]

3.16.68-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Andi Kleen <ak@xxxxxxxxxxxxxxx>

commit 6c4dbbd14730c43f4ed808a9c42ca41625925c22 upstream.

X86_FEATURE_MD_CLEAR is a new CPUID bit which is set when microcode
provides the mechanism to invoke a flush of various exploitable CPU buffers
by invoking the VERW instruction.

Hand it through to guests so they can adjust their mitigations.

This also requires corresponding qemu changes, which are available
separately.

[ tglx: Massaged changelog ]

Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Borislav Petkov <bp@xxxxxxx>
Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Reviewed-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Reviewed-by: Jon Masters <jcm@xxxxxxxxxx>
Tested-by: Jon Masters <jcm@xxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/x86/kvm/cpuid.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -320,7 +320,7 @@ static inline int __do_cpuid_ent(struct
 	/* cpuid 7.0.edx*/
 	const u32 kvm_cpuid_7_0_edx_x86_features =
 		F(SPEC_CTRL) | F(SPEC_CTRL_SSBD) | F(ARCH_CAPABILITIES) |
-		F(INTEL_STIBP);
+		F(INTEL_STIBP) | F(MD_CLEAR);
 
 	/* all calls to cpuid_count() should be made on the same cpu */
 	get_cpu();