powerpc/64s/exception: machine check fix KVM guest test

The machine_check_handle_early hypervisor guest test is skipped if
!HVMODE or MSR[HV]=0, which is wrong for PR or nested hypervisors
that could be running a guest in this state.

Test HSTATE_IN_GUEST up front and use that to branch out to the KVM
handler, then MSR[PR] alone can test for this kernel's userspace.
This matches all other interrupt handling.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190802105709.27696-4-npiggin@gmail.com

arch/powerpc/kernel/exceptions-64s.S

@@ -1108,11 +1108,8 @@ EXC_COMMON_BEGIN(machine_check_handle_early)
 	bl	machine_check_early
 	std	r3,RESULT(r1)	/* Save result */
 	ld	r12,_MSR(r1)
-BEGIN_FTR_SECTION
-	b	4f
-END_FTR_SECTION_IFCLR(CPU_FTR_HVMODE)
 
-#ifdef	CONFIG_PPC_P7_NAP
+#ifdef CONFIG_PPC_P7_NAP
 	/*
 	 * Check if thread was in power saving mode. We come here when any
 	 * of the following is true:
@@ -1128,30 +1125,26 @@ BEGIN_FTR_SECTION
 END_FTR_SECTION_IFSET(CPU_FTR_HVMODE | CPU_FTR_ARCH_206)
 #endif
 
-	/*
-	 * Check if we are coming from hypervisor userspace. If yes then we
-	 * continue in host kernel in V mode to deliver the MC event.
-	 */
-	rldicl.	r11,r12,4,63		/* See if MC hit while in HV mode. */
-	beq	5f
-4:	andi.	r11,r12,MSR_PR		/* See if coming from user. */
-	bne	9f			/* continue in V mode if we are. */
-
-5:
 #ifdef CONFIG_KVM_BOOK3S_64_HANDLER
-BEGIN_FTR_SECTION
 	/*
-	 * We are coming from kernel context. Check if we are coming from
-	 * guest. if yes, then we can continue. We will fall through
-	 * do_kvm_200->kvmppc_interrupt to deliver the MC event to guest.
+	 * Check if we are coming from guest. If yes, then run the normal
+	 * exception handler which will take the do_kvm_200->kvmppc_interrupt
+	 * branch to deliver the MC event to guest.
 	 */
 	lbz	r11,HSTATE_IN_GUEST(r13)
 	cmpwi	r11,0			/* Check if coming from guest */
 	bne	9f			/* continue if we are. */
-END_FTR_SECTION_IFSET(CPU_FTR_HVMODE)
 #endif
+
+	/*
+	 * Check if we are coming from userspace. If yes, then run the normal
+	 * exception handler which will deliver the MC event to this kernel.
+	 */
+	andi.	r11,r12,MSR_PR		/* See if coming from user. */
+	bne	9f			/* continue in V mode if we are. */
+
 	/*
-	 * At this point we are not sure about what context we come from.
+	 * At this point we are coming from kernel context.
 	 * Queue up the MCE event and return from the interrupt.
 	 * But before that, check if this is an un-recoverable exception.
 	 * If yes, then stay on emergency stack and panic.