KVM: x86: preserve the high 32-bits of the PAT register

commit 7cb060a9 upstream.

KVM does not really do much with the PAT, so this went unnoticed for a
long time.  It is exposed however if you try to do rdmsr on the PAT
register.
Reported-by: Valentine Sinitsyn <valentine.sinitsyn@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

arch/x86/include/asm/kvm_host.h

@@ -418,7 +418,7 @@ struct kvm_vcpu_arch {
 	bool nmi_injected;    /* Trying to inject an NMI this entry */
 
 	struct mtrr_state_type mtrr_state;
-	u32 pat;
+	u64 pat;
 
 	int switch_db_regs;
 	unsigned long db[KVM_NR_DB_REGS];