KVM: x86/pvm: Remove SWITCH_FLAGS_NMI_WIN

SWITCH_FLAGS_IRQ_WIN is used instead and add the comment on it.

Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>

Author: Lai Jiangshan

arch/x86/kvm/pvm/pvm.c

@@ -1589,8 +1589,13 @@ static int __do_pvm_event(struct kvm_vcpu *vcpu, bool user, int vector,
 		 * correspondingly.
 		 *
 		 * The guest should check async exceptions when it clears any
-		 * PVM_PVCS_EVENT_VECTOR_* bits.  The hypervisor should check
-		 * async exceptions when handling ERETU/ERETS.
+		 * PVM_PVCS_EVENT_VECTOR_* bits.
+		 *
+		 * While the guest sets PVM_PVCS_EVENT_VECTOR_STD before
+		 * invoking ERETU/ERETS, it cannot check for any async
+		 * exceptions in an atomic way. Instead, it relies on the
+		 * hypervisor to check for any unhandled async exceptions
+		 * when handling ERETU/ERETS.
 		 */
 		if (vector == NMI_VECTOR)
 			pvcs->event_vector |= PVM_PVCS_EVENT_VECTOR_NMI;
@@ -1600,8 +1605,13 @@ static int __do_pvm_event(struct kvm_vcpu *vcpu, bool user, int vector,
 			kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
 
 		/*
-		 * Set SWITCH_FLAGS_IRQ_WIN to stop the guest to directly
-		 * switch to the user mode.
+		 * Reuse SWITCH_FLAGS_IRQ_WIN to force the guest ERETU back to
+		 * the hypervisor to meet the requirement stipulated above in
+		 * case it is on the path to ERETU.
+		 *
+		 * When forced back to handle_synthetic_instruction_return(),
+		 * SWITCH_FLAGS_IRQ_WIN will be cleared in kvm_set_rflags() or
+		 * unhandled NMI/MCE will be reinjected.
 		 */
 		to_pvm(vcpu)->switch_flags |= SWITCH_FLAGS_IRQ_WIN;
 

arch/x86/kvm/pvm/pvm.h

@@ -11,17 +11,14 @@
  * IRQ_WIN:
  *	There is an irq window request, and the vcpu should not directly
  *	switch to context with IRQ enabled, e.g. user mode.
- * NMI_WIN:
- *	There is an NMI window request.
  * SINGLE_STEP:
  *	KVM_GUESTDBG_SINGLESTEP is set.
  * PVCS_INVALID:
  *	The GPC of PVCS is invalid and khva is NULL.
  */
 #define SWITCH_FLAGS_IRQ_WIN				_BITULL(8)
-#define SWITCH_FLAGS_NMI_WIN				_BITULL(9)
-#define SWITCH_FLAGS_SINGLE_STEP			_BITULL(10)
-#define SWITCH_FLAGS_PVCS_INVALID			_BITULL(11)
+#define SWITCH_FLAGS_SINGLE_STEP			_BITULL(9)
+#define SWITCH_FLAGS_PVCS_INVALID			_BITULL(10)
 
 #define SWITCH_FLAGS_INIT	(SWITCH_FLAGS_SMOD | SWITCH_FLAGS_PVCS_INVALID)