Mask AMD CPUID masks in software before writing them to the MSRs

Mask AMD CPUID masks in software before writing them to the MSRs.
Setting bits in the CPUID mask MSR that are not set in the unmasked
CPUID response can cause those bits to be set in the masked response.
Avoid that by explicitly masking in software.

Signed-off-by: Tim Deegan <Tim.Deegan@citrix.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/xen/arch/x86/cpu/amd.c b/xen/arch/x86/cpu/amd.c
index 94f35770e5..aabfd4c9ba 100644
--- a/xen/arch/x86/cpu/amd.c
+++ b/xen/arch/x86/cpu/amd.c
@@ -130,6 +130,14 @@ static void __devinit set_cpuidmask(struct cpuinfo_x86 *c)
 		return;
 	}
 
+        /* Setting bits in the CPUID mask MSR that are not set in the
+         * unmasked CPUID response can cause those bits to be set in the
+         * masked response.  Avoid that by explicitly masking in software. */
+        feat_ecx &= cpuid_ecx(0x00000001);
+        feat_edx &= cpuid_edx(0x00000001);
+        extfeat_ecx &= cpuid_ecx(0x80000001);
+        extfeat_edx &= cpuid_edx(0x80000001);
+
 	status = set_mask;
 	printk("Writing CPUID feature mask ECX:EDX -> %08Xh:%08Xh\n", 
 	       feat_ecx, feat_edx);