KVM: x86: Always set kvm_run->if_flag

The kvm_run struct's if_flag is a part of the userspace/kernel API. The
SEV-ES patches failed to set this flag because it's no longer needed by
QEMU (according to the comment in the source code). However, other
hypervisors may make use of this flag. Therefore, set the flag for
guests with encrypted registers (i.e., with guest_state_protected set).

Fixes: f1c6366e ("KVM: SVM: Add required changes to support intercepts under SEV-ES")
Signed-off-by: Marc Orr <marcorr@google.com>
Message-Id: <20211209155257.128747-1-marcorr@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

arch/x86/include/asm/kvm-x86-ops.h

@@ -47,6 +47,7 @@ KVM_X86_OP(set_dr7)
 KVM_X86_OP(cache_reg)
 KVM_X86_OP(get_rflags)
 KVM_X86_OP(set_rflags)
+KVM_X86_OP(get_if_flag)
 KVM_X86_OP(tlb_flush_all)
 KVM_X86_OP(tlb_flush_current)
 KVM_X86_OP_NULL(tlb_remote_flush)

arch/x86/include/asm/kvm_host.h

@@ -1349,6 +1349,7 @@ struct kvm_x86_ops {
 	void (*cache_reg)(struct kvm_vcpu *vcpu, enum kvm_reg reg);
 	unsigned long (*get_rflags)(struct kvm_vcpu *vcpu);
 	void (*set_rflags)(struct kvm_vcpu *vcpu, unsigned long rflags);
+	bool (*get_if_flag)(struct kvm_vcpu *vcpu);
 
 	void (*tlb_flush_all)(struct kvm_vcpu *vcpu);
 	void (*tlb_flush_current)(struct kvm_vcpu *vcpu);

arch/x86/kvm/svm/svm.c

@@ -1585,6 +1585,15 @@ static void svm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
 	to_svm(vcpu)->vmcb->save.rflags = rflags;
 }
 
+static bool svm_get_if_flag(struct kvm_vcpu *vcpu)
+{
+	struct vmcb *vmcb = to_svm(vcpu)->vmcb;
+
+	return sev_es_guest(vcpu->kvm)
+		? vmcb->control.int_state & SVM_GUEST_INTERRUPT_MASK
+		: kvm_get_rflags(vcpu) & X86_EFLAGS_IF;
+}
+
 static void svm_cache_reg(struct kvm_vcpu *vcpu, enum kvm_reg reg)
 {
 	switch (reg) {
@@ -3568,14 +3577,7 @@ bool svm_interrupt_blocked(struct kvm_vcpu *vcpu)
 	if (!gif_set(svm))
 		return true;
 
-	if (sev_es_guest(vcpu->kvm)) {
-		/*
-		 * SEV-ES guests to not expose RFLAGS. Use the VMCB interrupt mask
-		 * bit to determine the state of the IF flag.
-		 */
-		if (!(vmcb->control.int_state & SVM_GUEST_INTERRUPT_MASK))
-			return true;
-	} else if (is_guest_mode(vcpu)) {
+	if (is_guest_mode(vcpu)) {
 		/* As long as interrupts are being delivered...  */
 		if ((svm->nested.ctl.int_ctl & V_INTR_MASKING_MASK)
 		    ? !(svm->vmcb01.ptr->save.rflags & X86_EFLAGS_IF)
@@ -3586,7 +3588,7 @@ bool svm_interrupt_blocked(struct kvm_vcpu *vcpu)
 		if (nested_exit_on_intr(svm))
 			return false;
 	} else {
-		if (!(kvm_get_rflags(vcpu) & X86_EFLAGS_IF))
+		if (!svm_get_if_flag(vcpu))
 			return true;
 	}
 
@@ -4621,6 +4623,7 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
 	.cache_reg = svm_cache_reg,
 	.get_rflags = svm_get_rflags,
 	.set_rflags = svm_set_rflags,
+	.get_if_flag = svm_get_if_flag,
 
 	.tlb_flush_all = svm_flush_tlb,
 	.tlb_flush_current = svm_flush_tlb,

arch/x86/kvm/vmx/vmx.c

@@ -1363,6 +1363,11 @@ void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
 		vmx->emulation_required = vmx_emulation_required(vcpu);
 }
 
+static bool vmx_get_if_flag(struct kvm_vcpu *vcpu)
+{
+	return vmx_get_rflags(vcpu) & X86_EFLAGS_IF;
+}
+
 u32 vmx_get_interrupt_shadow(struct kvm_vcpu *vcpu)
 {
 	u32 interruptibility = vmcs_read32(GUEST_INTERRUPTIBILITY_INFO);
@@ -7579,6 +7584,7 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = {
 	.cache_reg = vmx_cache_reg,
 	.get_rflags = vmx_get_rflags,
 	.set_rflags = vmx_set_rflags,
+	.get_if_flag = vmx_get_if_flag,
 
 	.tlb_flush_all = vmx_flush_tlb_all,
 	.tlb_flush_current = vmx_flush_tlb_current,

arch/x86/kvm/x86.c

@@ -9001,14 +9001,7 @@ static void post_kvm_run_save(struct kvm_vcpu *vcpu)
 {
 	struct kvm_run *kvm_run = vcpu->run;
 
-	/*
-	 * if_flag is obsolete and useless, so do not bother
-	 * setting it for SEV-ES guests.  Userspace can just
-	 * use kvm_run->ready_for_interrupt_injection.
-	 */
-	kvm_run->if_flag = !vcpu->arch.guest_state_protected
-		&& (kvm_get_rflags(vcpu) & X86_EFLAGS_IF) != 0;
-
+	kvm_run->if_flag = static_call(kvm_x86_get_if_flag)(vcpu);
 	kvm_run->cr8 = kvm_get_cr8(vcpu);
 	kvm_run->apic_base = kvm_get_apic_base(vcpu);