KVM: Fix mov cr4 #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

@@ -599,7 +599,7 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int reason,
 
 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);
+int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4);
 void kvm_set_cr8(struct kvm_vcpu *vcpu, unsigned long cr8);
 int kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val);
 int kvm_get_dr(struct kvm_vcpu *vcpu, int dr, unsigned long *val);

arch/x86/kvm/vmx.c

@@ -3189,8 +3189,8 @@ static int handle_cr(struct kvm_vcpu *vcpu)
 			skip_emulated_instruction(vcpu);
 			return 1;
 		case 4:
-			kvm_set_cr4(vcpu, val);
-			skip_emulated_instruction(vcpu);
+			err = kvm_set_cr4(vcpu, val);
+			complete_insn_gp(vcpu, err);
 			return 1;
 		case 8: {
 				u8 cr8_prev = kvm_get_cr8(vcpu);

arch/x86/kvm/x86.c

@@ -531,7 +531,7 @@ static void update_cpuid(struct kvm_vcpu *vcpu)
 	}
 }
 
-int __kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
+int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 {
 	unsigned long old_cr4 = kvm_read_cr4(vcpu);
 	unsigned long pdptr_bits = X86_CR4_PGE | X86_CR4_PSE | X86_CR4_PAE;
@@ -563,12 +563,6 @@ int __kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 
 	return 0;
 }
-
-void kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
-{
-	if (__kvm_set_cr4(vcpu, cr4))
-		kvm_inject_gp(vcpu, 0);
-}
 EXPORT_SYMBOL_GPL(kvm_set_cr4);
 
 static int __kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
@@ -3735,7 +3729,7 @@ static int emulator_set_cr(int cr, unsigned long val, struct kvm_vcpu *vcpu)
 		res = __kvm_set_cr3(vcpu, val);
 		break;
 	case 4:
-		res = __kvm_set_cr4(vcpu, mk_cr_64(kvm_read_cr4(vcpu), val));
+		res = kvm_set_cr4(vcpu, mk_cr_64(kvm_read_cr4(vcpu), val));
 		break;
 	case 8:
 		res = __kvm_set_cr8(vcpu, val & 0xfUL);