KVM: SVM: Truncate GPR value for DR and CR accesses in !64-bit mode

Drop bits 63:32 on loads/stores to/from DRs and CRs when the vCPU is not
in 64-bit mode.  The APM states bits 63:32 are dropped for both DRs and
CRs:

  In 64-bit mode, the operand size is fixed at 64 bits without the need
  for a REX prefix. In non-64-bit mode, the operand size is fixed at 32
  bits and the upper 32 bits of the destination are forced to 0.

Fixes: 7ff76d58 ("KVM: SVM: enhance MOV CR intercept handler")
Fixes: cae3797a ("KVM: SVM: enhance mov DR intercept handler")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210422022128.3464144-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/svm.c

@@ -2451,7 +2451,7 @@ static int cr_interception(struct kvm_vcpu *vcpu)
 	err = 0;
 	if (cr >= 16) { /* mov to cr */
 		cr -= 16;
-		val = kvm_register_read(vcpu, reg);
+		val = kvm_register_readl(vcpu, reg);
 		trace_kvm_cr_write(cr, val);
 		switch (cr) {
 		case 0:
@@ -2497,7 +2497,7 @@ static int cr_interception(struct kvm_vcpu *vcpu)
 			kvm_queue_exception(vcpu, UD_VECTOR);
 			return 1;
 		}
-		kvm_register_write(vcpu, reg, val);
+		kvm_register_writel(vcpu, reg, val);
 		trace_kvm_cr_read(cr, val);
 	}
 	return kvm_complete_insn_gp(vcpu, err);
@@ -2563,11 +2563,11 @@ static int dr_interception(struct kvm_vcpu *vcpu)
 	dr = svm->vmcb->control.exit_code - SVM_EXIT_READ_DR0;
 	if (dr >= 16) { /* mov to DRn  */
 		dr -= 16;
-		val = kvm_register_read(vcpu, reg);
+		val = kvm_register_readl(vcpu, reg);
 		err = kvm_set_dr(vcpu, dr, val);
 	} else {
 		kvm_get_dr(vcpu, dr, &val);
-		kvm_register_write(vcpu, reg, val);
+		kvm_register_writel(vcpu, reg, val);
 	}
 
 	return kvm_complete_insn_gp(vcpu, err);