KVM: SVM: preserve VGIF across VMCB switch

There is only one GIF flag for the whole processor, so make sure it is not clobbered
when switching to L2 (in which case we also have to include the V_GIF_ENABLE_MASK,
lest we confuse enable_gif/disable_gif/gif_set).  When going back, L1 could in
theory have entered L2 without issuing a CLGI so make sure the svm_set_gif is
done last, after svm->vmcb->control.int_ctl has been copied back from hsave.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/nested.c

@@ -293,6 +293,7 @@ static void nested_prepare_vmcb_save(struct vcpu_svm *svm, struct vmcb *nested_v
 
 static void nested_prepare_vmcb_control(struct vcpu_svm *svm)
 {
+	const u32 mask = V_INTR_MASKING_MASK | V_GIF_ENABLE_MASK | V_GIF_MASK;
 	if (svm->nested.ctl.nested_ctl & SVM_NESTED_CTL_NP_ENABLE)
 		nested_svm_init_mmu_context(&svm->vcpu);
 
@@ -308,7 +309,10 @@ static void nested_prepare_vmcb_control(struct vcpu_svm *svm)
 	svm->vmcb->control.tsc_offset = svm->vcpu.arch.tsc_offset =
 		svm->vcpu.arch.l1_tsc_offset + svm->nested.ctl.tsc_offset;
 
-	svm->vmcb->control.int_ctl             = svm->nested.ctl.int_ctl | V_INTR_MASKING_MASK;
+	svm->vmcb->control.int_ctl             =
+		(svm->nested.ctl.int_ctl & ~mask) |
+		(svm->nested.hsave->control.int_ctl & mask);
+
 	svm->vmcb->control.virt_ext            = svm->nested.ctl.virt_ext;
 	svm->vmcb->control.int_vector          = svm->nested.ctl.int_vector;
 	svm->vmcb->control.int_state           = svm->nested.ctl.int_state;