[PATCH v5 2/2] KVM: PPC: Exit guest upon MCE when FWNMI capability is enabled

@@ -123,6 +123,7 @@ MODULE_PARM_DESC(halt_poll_ns_shrink, "Factor halt poll time is shrunk by");
 
 static void kvmppc_end_cede(struct kvm_vcpu *vcpu);
 static int kvmppc_hv_setup_htab_rma(struct kvm_vcpu *vcpu);
+static void kvmppc_machine_check_hook(void);
 
 static inline struct kvm_vcpu *next_runnable_thread(struct kvmppc_vcore *vc,
 		int *ip)

@@ -954,15 +955,14 @@ static int kvmppc_handle_exit_hv(struct kvm_run *run, struct kvm_vcpu *vcpu,
 		r = RESUME_GUEST;
 		break;
 	case BOOK3S_INTERRUPT_MACHINE_CHECK:
+		/* Exit to guest with KVM_EXIT_NMI as exit reason */
+		run->exit_reason = KVM_EXIT_NMI;
+		r = RESUME_HOST;
 		/*
-		 * Deliver a machine check interrupt to the guest.
-		 * We have to do this, even if the host has handled the
-		 * machine check, because machine checks use SRR0/1 and
-		 * the interrupt might have trashed guest state in them.
+		 * Invoke host-kernel handler to perform any host-side
+		 * handling before exiting the guest.
 		 */
-		kvmppc_book3s_queue_irqprio(vcpu,
-					    BOOK3S_INTERRUPT_MACHINE_CHECK);
-		r = RESUME_GUEST;
+		kvmppc_machine_check_hook();
 		break;
 	case BOOK3S_INTERRUPT_PROGRAM:
 	{

@@ -3491,6 +3491,19 @@ static void kvmppc_irq_bypass_del_producer_hv(struct irq_bypass_consumer *cons,
 }
 #endif
 
+/*
+ * Hook to handle machine check exceptions occurred inside a guest.
+ * This hook is invoked from host virtual mode from KVM before exiting
+ * the guest with KVM_EXIT_NMI exit reason. This gives an opportunity
+ * for the host to take action (if any) before passing on the machine
+ * check exception to the guest kernel.
+ */
+static void kvmppc_machine_check_hook(void)
+{
+	if (ppc_md.machine_check_exception)
+		ppc_md.machine_check_exception(NULL);
+}
+
 static long kvm_arch_vm_ioctl_hv(struct file *filp,
 				 unsigned int ioctl, unsigned long arg)
 {

@@ -134,21 +134,18 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
 	stb	r0, HSTATE_HWTHREAD_REQ(r13)
 
 	/*
-	 * For external and machine check interrupts, we need
-	 * to call the Linux handler to process the interrupt.
-	 * We do that by jumping to absolute address 0x500 for
-	 * external interrupts, or the machine_check_fwnmi label
-	 * for machine checks (since firmware might have patched
-	 * the vector area at 0x200).  The [h]rfid at the end of the
-	 * handler will return to the book3s_hv_interrupts.S code.
-	 * For other interrupts we do the rfid to get back
-	 * to the book3s_hv_interrupts.S code here.
+	 * For external interrupts we need to call the Linux
+	 * handler to process the interrupt. We do that by jumping
+	 * to absolute address 0x500 for external interrupts.
+	 * The [h]rfid at the end of the handler will return to
+	 * the book3s_hv_interrupts.S code. For other interrupts
+	 * we do the rfid to get back to the book3s_hv_interrupts.S
+	 * code here.
 	 */
 	ld	r8, 112+PPC_LR_STKOFF(r1)
 	addi	r1, r1, 112
 	ld	r7, HSTATE_HOST_MSR(r13)
 
-	cmpwi	cr1, r12, BOOK3S_INTERRUPT_MACHINE_CHECK
 	cmpwi	r12, BOOK3S_INTERRUPT_EXTERNAL
 	beq	11f
 	cmpwi	r12, BOOK3S_INTERRUPT_H_DOORBELL

@@ -163,7 +160,10 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
 	mtmsrd	r6, 1			/* Clear RI in MSR */
 	mtsrr0	r8
 	mtsrr1	r7
-	beq	cr1, 13f		/* machine check */
+	/*
+	 * BOOK3S_INTERRUPT_MACHINE_CHECK is handled at the
+	 * time of guest exit
+	 */
 	RFI
 
 	/* On POWER7, we have external interrupts set to use HSRR0/1 */

@@ -171,8 +171,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
 	mtspr	SPRN_HSRR1, r7
 	ba	0x500
 
-13:	b	machine_check_fwnmi
-
 14:	mtspr	SPRN_HSRR0, r8
 	mtspr	SPRN_HSRR1, r7
 	b	hmi_exception_after_realmode

@@ -2338,15 +2336,13 @@ machine_check_realmode:
 	ld	r9, HSTATE_KVM_VCPU(r13)
 	li	r12, BOOK3S_INTERRUPT_MACHINE_CHECK
 	/*
-	 * Deliver unhandled/fatal (e.g. UE) MCE errors to guest through
-	 * machine check interrupt (set HSRR0 to 0x200). And for handled
-	 * errors (no-fatal), just go back to guest execution with current
-	 * HSRR0 instead of exiting guest. This new approach will inject
-	 * machine check to guest for fatal error causing guest to crash.
-	 *
-	 * The old code used to return to host for unhandled errors which
-	 * was causing guest to hang with soft lockups inside guest and
-	 * makes it difficult to recover guest instance.
+	 * Deliver unhandled/fatal (e.g. UE) MCE errors to guest either
+	 * through machine check interrupt (set HSRR0 to 0x200) or by
+	 * exiting the guest with KVM_EXIT_NMI exit reason if guest is
+	 * FWNMI capable. For handled errors (no-fatal), just go back
+	 * to guest execution with current HSRR0. This new approach
+	 * injects machine check errors in guest address space to guest
+	 * enabling guest kernel to suitably handle such errors.
 	 *
 	 * if we receive machine check with MSR(RI=0) then deliver it to
 	 * guest as machine check causing guest to crash.

@@ -2360,7 +2356,12 @@ machine_check_realmode:
 	cmpdi	r3, 0		/* Did we handle MCE ? */
 	bne	2f	/* Continue guest execution. */
 	/* If not, deliver a machine check.  SRR0/1 are already set */
-1:	li	r10, BOOK3S_INTERRUPT_MACHINE_CHECK
+	/* Check if guest is capable of handling NMI exit */
+1:	ld	r3, VCPU_KVM(r9)
+	lbz	r3, KVM_FWNMI(r3)
+	cmpdi	r3, 1       /* FWNMI capable? */
+	beq	mc_cont
+	li	r10, BOOK3S_INTERRUPT_MACHINE_CHECK
 	bl	kvmppc_msr_interrupt
 2:	b	fast_interrupt_c_return
 

@@ -446,6 +446,16 @@ int opal_machine_check(struct pt_regs *regs)
 	}
 	machine_check_print_event_info(&evt);
 
+	/*
+	 * If regs is NULL, then the machine check exception occurred
+	 * in the guest. Currently no action is performed in the host
+	 * other than printing the event information. The machine check
+	 * exception is passed on to the guest kernel and the guest
+	 * kernel will attempt for recovery.
+	 */
+	if (!regs)
+		return 0;
+
 	if (opal_recover_mce(regs, &evt))
 		return 1;