KVM: nVMX: Handle split-lock #AC exceptions that happen in L2

Mark #ACs that won't be reinjected to the guest as wanted by L0 so that
KVM handles split-lock #AC from L2 instead of forwarding the exception to
L1.  Split-lock #AC isn't yet virtualized, i.e. L1 will treat it like a
regular #AC and do the wrong thing, e.g. reinject it into L2.

Fixes: e6f8b6c1 ("KVM: VMX: Extend VMXs #AC interceptor to handle split lock #AC in guest")
Cc: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210622172244.3561540-1-seanjc@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/nested.c

@@ -5833,6 +5833,9 @@ static bool nested_vmx_l0_wants_exit(struct kvm_vcpu *vcpu,
 		else if (is_breakpoint(intr_info) &&
 			 vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP)
 			return true;
+		else if (is_alignment_check(intr_info) &&
+			 !vmx_guest_inject_ac(vcpu))
+			return true;
 		return false;
 	case EXIT_REASON_EXTERNAL_INTERRUPT:
 		return true;

arch/x86/kvm/vmx/vmcs.h

@@ -117,6 +117,11 @@ static inline bool is_gp_fault(u32 intr_info)
 	return is_exception_n(intr_info, GP_VECTOR);
 }
 
+static inline bool is_alignment_check(u32 intr_info)
+{
+	return is_exception_n(intr_info, AC_VECTOR);
+}
+
 static inline bool is_machine_check(u32 intr_info)
 {
 	return is_exception_n(intr_info, MC_VECTOR);

arch/x86/kvm/vmx/vmx.c

@@ -4743,7 +4743,7 @@ static int handle_machine_check(struct kvm_vcpu *vcpu)
  *  - Guest has #AC detection enabled in CR0
  *  - Guest EFLAGS has AC bit set
  */
-static inline bool guest_inject_ac(struct kvm_vcpu *vcpu)
+bool vmx_guest_inject_ac(struct kvm_vcpu *vcpu)
 {
 	if (!boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT))
 		return true;
@@ -4851,7 +4851,7 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
 		kvm_run->debug.arch.exception = ex_no;
 		break;
 	case AC_VECTOR:
-		if (guest_inject_ac(vcpu)) {
+		if (vmx_guest_inject_ac(vcpu)) {
 			kvm_queue_exception_e(vcpu, AC_VECTOR, error_code);
 			return 1;
 		}

arch/x86/kvm/vmx/vmx.h

@@ -376,6 +376,7 @@ void vmx_get_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg);
 void vmx_set_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg);
 u64 construct_eptp(struct kvm_vcpu *vcpu, hpa_t root_hpa, int root_level);
 
+bool vmx_guest_inject_ac(struct kvm_vcpu *vcpu);
 void vmx_update_exception_bitmap(struct kvm_vcpu *vcpu);
 void vmx_update_msr_bitmap(struct kvm_vcpu *vcpu);
 bool vmx_nmi_blocked(struct kvm_vcpu *vcpu);