KVM: Fix mov cr0 #GP at wrong instruction

On Intel, we call skip_emulated_instruction() even if we injected a #GP,
resulting in the #GP pointing at the wrong address.

Fix by injecting the exception and skipping the instruction at the same place,
so we can do just one or the other.
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -597,7 +597,7 @@ int kvm_load_segment_descriptor(struct kvm_vcpu *vcpu, u16 selector, int seg);
 int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int reason,
 		    bool has_error_code, u32 error_code);
 
-void kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0);
+int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0);
 void kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3);
 void kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4);
 void kvm_set_cr8(struct kvm_vcpu *vcpu, unsigned long cr8);

arch/x86/kvm/svm.c

@@ -807,7 +807,7 @@ static void init_vmcb(struct vcpu_svm *svm)
 	 * svm_set_cr0() sets PG and WP and clears NW and CD on save->cr0.
 	 */
 	svm->vcpu.arch.cr0 = X86_CR0_NW | X86_CR0_CD | X86_CR0_ET;
-	kvm_set_cr0(&svm->vcpu, svm->vcpu.arch.cr0);
+	(void)kvm_set_cr0(&svm->vcpu, svm->vcpu.arch.cr0);
 
 	save->cr4 = X86_CR4_PAE;
 	/* rdx = ?? */

arch/x86/kvm/vmx.c

@@ -3157,11 +3157,20 @@ vmx_patch_hypercall(struct kvm_vcpu *vcpu, unsigned char *hypercall)
 	hypercall[2] = 0xc1;
 }
 
+static void complete_insn_gp(struct kvm_vcpu *vcpu, int err)
+{
+	if (err)
+		kvm_inject_gp(vcpu, 0);
+	else
+		skip_emulated_instruction(vcpu);
+}
+
 static int handle_cr(struct kvm_vcpu *vcpu)
 {
 	unsigned long exit_qualification, val;
 	int cr;
 	int reg;
+	int err;
 
 	exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
 	cr = exit_qualification & 15;
@@ -3172,8 +3181,8 @@ static int handle_cr(struct kvm_vcpu *vcpu)
 		trace_kvm_cr_write(cr, val);
 		switch (cr) {
 		case 0:
-			kvm_set_cr0(vcpu, val);
-			skip_emulated_instruction(vcpu);
+			err = kvm_set_cr0(vcpu, val);
+			complete_insn_gp(vcpu, err);
 			return 1;
 		case 3:
 			kvm_set_cr3(vcpu, val);

arch/x86/kvm/x86.c

@@ -425,7 +425,7 @@ static bool pdptrs_changed(struct kvm_vcpu *vcpu)
 	return changed;
 }
 
-static int __kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
+int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
 {
 	unsigned long old_cr0 = kvm_read_cr0(vcpu);
 	unsigned long update_bits = X86_CR0_PG | X86_CR0_WP |
@@ -468,17 +468,11 @@ static int __kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
 		kvm_mmu_reset_context(vcpu);
 	return 0;
 }
-
-void kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
-{
-	if (__kvm_set_cr0(vcpu, cr0))
-		kvm_inject_gp(vcpu, 0);
-}
 EXPORT_SYMBOL_GPL(kvm_set_cr0);
 
 void kvm_lmsw(struct kvm_vcpu *vcpu, unsigned long msw)
 {
-	kvm_set_cr0(vcpu, kvm_read_cr0_bits(vcpu, ~0x0eul) | (msw & 0x0f));
+	(void)kvm_set_cr0(vcpu, kvm_read_cr0_bits(vcpu, ~0x0eul) | (msw & 0x0f));
 }
 EXPORT_SYMBOL_GPL(kvm_lmsw);
 
@@ -3732,7 +3726,7 @@ static int emulator_set_cr(int cr, unsigned long val, struct kvm_vcpu *vcpu)
 
 	switch (cr) {
 	case 0:
-		res = __kvm_set_cr0(vcpu, mk_cr_64(kvm_read_cr0(vcpu), val));
+		res = kvm_set_cr0(vcpu, mk_cr_64(kvm_read_cr0(vcpu), val));
 		break;
 	case 2:
 		vcpu->arch.cr2 = val;