KVM: x86: allow kvm_x86_ops.set_efer to return an error value

This will be used to signal an error to the userspace, in case
the vendor code failed during handling of this msr. (e.g -ENOMEM)
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20201001112954.6258-4-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -1101,7 +1101,7 @@ struct kvm_x86_ops {
 	void (*get_cs_db_l_bits)(struct kvm_vcpu *vcpu, int *db, int *l);
 	void (*set_cr0)(struct kvm_vcpu *vcpu, unsigned long cr0);
 	int (*set_cr4)(struct kvm_vcpu *vcpu, unsigned long cr4);
-	void (*set_efer)(struct kvm_vcpu *vcpu, u64 efer);
+	int (*set_efer)(struct kvm_vcpu *vcpu, u64 efer);
 	void (*get_idt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt);
 	void (*set_idt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt);
 	void (*get_gdt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt);

arch/x86/kvm/svm/svm.c

@@ -263,7 +263,7 @@ static int get_max_npt_level(void)
 #endif
 }
 
-void svm_set_efer(struct kvm_vcpu *vcpu, u64 efer)
+int svm_set_efer(struct kvm_vcpu *vcpu, u64 efer)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 	vcpu->arch.efer = efer;
@@ -283,6 +283,7 @@ void svm_set_efer(struct kvm_vcpu *vcpu, u64 efer)
 
 	svm->vmcb->save.efer = efer | EFER_SVME;
 	vmcb_mark_dirty(svm->vmcb, VMCB_CR);
+	return 0;
 }
 
 static int is_external_interrupt(u32 info)

arch/x86/kvm/svm/svm.h

@@ -350,7 +350,7 @@ static inline bool gif_set(struct vcpu_svm *svm)
 #define MSR_INVALID				0xffffffffU
 
 u32 svm_msrpm_offset(u32 msr);
-void svm_set_efer(struct kvm_vcpu *vcpu, u64 efer);
+int svm_set_efer(struct kvm_vcpu *vcpu, u64 efer);
 void svm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0);
 int svm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4);
 void svm_flush_tlb(struct kvm_vcpu *vcpu);

arch/x86/kvm/vmx/vmx.c

@@ -2815,13 +2815,14 @@ static void enter_rmode(struct kvm_vcpu *vcpu)
 	kvm_mmu_reset_context(vcpu);
 }
 
-void vmx_set_efer(struct kvm_vcpu *vcpu, u64 efer)
+int vmx_set_efer(struct kvm_vcpu *vcpu, u64 efer)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	struct vmx_uret_msr *msr = vmx_find_uret_msr(vmx, MSR_EFER);
 
+	/* Nothing to do if hardware doesn't support EFER. */
 	if (!msr)
-		return;
+		return 0;
 
 	vcpu->arch.efer = efer;
 	if (efer & EFER_LMA) {
@@ -2833,6 +2834,7 @@ void vmx_set_efer(struct kvm_vcpu *vcpu, u64 efer)
 		msr->data = efer & ~EFER_LME;
 	}
 	setup_msrs(vmx);
+	return 0;
 }
 
 #ifdef CONFIG_X86_64

arch/x86/kvm/vmx/vmx.h

@@ -319,7 +319,7 @@ unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu);
 void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags);
 u32 vmx_get_interrupt_shadow(struct kvm_vcpu *vcpu);
 void vmx_set_interrupt_shadow(struct kvm_vcpu *vcpu, int mask);
-void vmx_set_efer(struct kvm_vcpu *vcpu, u64 efer);
+int vmx_set_efer(struct kvm_vcpu *vcpu, u64 efer);
 void vmx_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0);
 int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4);
 void set_cr4_guest_host_mask(struct vcpu_vmx *vmx);

arch/x86/kvm/x86.c

@@ -1457,6 +1457,7 @@ static int set_efer(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 {
 	u64 old_efer = vcpu->arch.efer;
 	u64 efer = msr_info->data;
+	int r;
 
 	if (efer & efer_reserved_bits)
 		return 1;
@@ -1473,7 +1474,11 @@ static int set_efer(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	efer &= ~EFER_LMA;
 	efer |= vcpu->arch.efer & EFER_LMA;
 
-	kvm_x86_ops.set_efer(vcpu, efer);
+	r = kvm_x86_ops.set_efer(vcpu, efer);
+	if (r) {
+		WARN_ON(r > 0);
+		return r;
+	}
 
 	/* Update reserved bits */
 	if ((efer ^ old_efer) & EFER_NX)