KVM: x86: Expose XSAVEERPTR to the guest

I was surprised to see that the guest reported `fxsave_leak' while the
host did not. After digging deeper I noticed that the bits are simply
masked out during enumeration.

The XSAVEERPTR feature is actually a bug fix on AMD which means the
kernel can disable a workaround.

Pass XSAVEERPTR to the guest if available on the host.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/cpuid.c

@@ -485,9 +485,9 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
 
 	/* cpuid 0x80000008.ebx */
 	const u32 kvm_cpuid_8000_0008_ebx_x86_features =
-		F(CLZERO) | F(WBNOINVD) | F(AMD_IBPB) | F(AMD_IBRS) |
-		F(AMD_STIBP) | F(AMD_STIBP_ALWAYS_ON) | F(AMD_SSBD) |
-		F(VIRT_SSBD) | F(AMD_SSB_NO);
+		F(CLZERO) | F(XSAVEERPTR) |
+		F(WBNOINVD) | F(AMD_IBPB) | F(AMD_IBRS) | F(AMD_SSBD) | F(VIRT_SSBD) |
+		F(AMD_SSB_NO) | F(AMD_STIBP) | F(AMD_STIBP_ALWAYS_ON);
 
 	/* cpuid 0xC0000001.edx */
 	const u32 kvm_cpuid_C000_0001_edx_x86_features =