powerpc/64s/powernv: Allow KVM to handle guest machine check details

KVM has strategies to perform machine check recovery. If a MCE hits
in a guest, have the low level handler just decode and save the MCE
but not try to recover anything, so KVM can deal with it.

The host does not own SLBs and does not need to report the SLB state
in case of a multi-hit for example, or know about the virtual memory
map of the guest.

UE and memory poisoning of guest pages in the host is one thing that
is possibly not completely robust at the moment, but this too needs
to go via KVM (possibly via the guest and back out to host via hcall)
rather than being handled at a low level in the host handler.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201128070728.825934-3-npiggin@gmail.com

arch/powerpc/kernel/mce.c

@@ -577,7 +577,7 @@ void machine_check_print_event_info(struct machine_check_event *evt,
 
 #ifdef CONFIG_PPC_BOOK3S_64
 	/* Display faulty slb contents for SLB errors. */
-	if (evt->error_type == MCE_ERROR_TYPE_SLB)
+	if (evt->error_type == MCE_ERROR_TYPE_SLB && !in_guest)
 		slb_dump_contents(local_paca->mce_faulty_slbs);
 #endif
 }

arch/powerpc/kernel/mce_power.c

@@ -62,21 +62,27 @@ unsigned long addr_to_pfn(struct pt_regs *regs, unsigned long addr)
 	return pfn;
 }
 
+static bool mce_in_guest(void)
+{
+#ifdef CONFIG_KVM_BOOK3S_HANDLER
+	/*
+	 * If machine check is hit when in guest context or low level KVM
+	 * code, avoid looking up any translations or making any attempts
+	 * to recover, just record the event and pass to KVM.
+	 */
+	if (get_paca()->kvm_hstate.in_guest)
+		return true;
+#endif
+	return false;
+}
+
 /* flush SLBs and reload */
 #ifdef CONFIG_PPC_BOOK3S_64
 void flush_and_reload_slb(void)
 {
 	/* Invalidate all SLBs */
 	slb_flush_all_realmode();
 
-#ifdef CONFIG_KVM_BOOK3S_HANDLER
-	/*
-	 * If machine check is hit when in guest or in transition, we will
-	 * only flush the SLBs and continue.
-	 */
-	if (get_paca()->kvm_hstate.in_guest)
-		return;
-#endif
 	if (early_radix_enabled())
 		return;
 
@@ -490,19 +496,21 @@ static int mce_handle_ierror(struct pt_regs *regs,
 		if ((srr1 & table[i].srr1_mask) != table[i].srr1_value)
 			continue;
 
-		/* attempt to correct the error */
-		switch (table[i].error_type) {
-		case MCE_ERROR_TYPE_SLB:
-			if (local_paca->in_mce == 1)
-				slb_save_contents(local_paca->mce_faulty_slbs);
-			handled = mce_flush(MCE_FLUSH_SLB);
-			break;
-		case MCE_ERROR_TYPE_ERAT:
-			handled = mce_flush(MCE_FLUSH_ERAT);
-			break;
-		case MCE_ERROR_TYPE_TLB:
-			handled = mce_flush(MCE_FLUSH_TLB);
-			break;
+		if (!mce_in_guest()) {
+			/* attempt to correct the error */
+			switch (table[i].error_type) {
+			case MCE_ERROR_TYPE_SLB:
+				if (local_paca->in_mce == 1)
+					slb_save_contents(local_paca->mce_faulty_slbs);
+				handled = mce_flush(MCE_FLUSH_SLB);
+				break;
+			case MCE_ERROR_TYPE_ERAT:
+				handled = mce_flush(MCE_FLUSH_ERAT);
+				break;
+			case MCE_ERROR_TYPE_TLB:
+				handled = mce_flush(MCE_FLUSH_TLB);
+				break;
+			}
 		}
 
 		/* now fill in mce_error_info */
@@ -534,7 +542,7 @@ static int mce_handle_ierror(struct pt_regs *regs,
 		mce_err->sync_error = table[i].sync_error;
 		mce_err->severity = table[i].severity;
 		mce_err->initiator = table[i].initiator;
-		if (table[i].nip_valid) {
+		if (table[i].nip_valid && !mce_in_guest()) {
 			*addr = regs->nip;
 			if (mce_err->sync_error &&
 				table[i].error_type == MCE_ERROR_TYPE_UE) {
@@ -577,22 +585,24 @@ static int mce_handle_derror(struct pt_regs *regs,
 		if (!(dsisr & table[i].dsisr_value))
 			continue;
 
-		/* attempt to correct the error */
-		switch (table[i].error_type) {
-		case MCE_ERROR_TYPE_SLB:
-			if (local_paca->in_mce == 1)
-				slb_save_contents(local_paca->mce_faulty_slbs);
-			if (mce_flush(MCE_FLUSH_SLB))
-				handled = 1;
-			break;
-		case MCE_ERROR_TYPE_ERAT:
-			if (mce_flush(MCE_FLUSH_ERAT))
-				handled = 1;
-			break;
-		case MCE_ERROR_TYPE_TLB:
-			if (mce_flush(MCE_FLUSH_TLB))
-				handled = 1;
-			break;
+		if (!mce_in_guest()) {
+			/* attempt to correct the error */
+			switch (table[i].error_type) {
+			case MCE_ERROR_TYPE_SLB:
+				if (local_paca->in_mce == 1)
+					slb_save_contents(local_paca->mce_faulty_slbs);
+				if (mce_flush(MCE_FLUSH_SLB))
+					handled = 1;
+				break;
+			case MCE_ERROR_TYPE_ERAT:
+				if (mce_flush(MCE_FLUSH_ERAT))
+					handled = 1;
+				break;
+			case MCE_ERROR_TYPE_TLB:
+				if (mce_flush(MCE_FLUSH_TLB))
+					handled = 1;
+				break;
+			}
 		}
 
 		/*
@@ -634,7 +644,7 @@ static int mce_handle_derror(struct pt_regs *regs,
 		mce_err->initiator = table[i].initiator;
 		if (table[i].dar_valid)
 			*addr = regs->dar;
-		else if (mce_err->sync_error &&
+		else if (mce_err->sync_error && !mce_in_guest() &&
 				table[i].error_type == MCE_ERROR_TYPE_UE) {
 			/*
 			 * We do a maximum of 4 nested MCE calls, see
@@ -662,7 +672,8 @@ static int mce_handle_derror(struct pt_regs *regs,
 static long mce_handle_ue_error(struct pt_regs *regs,
 				struct mce_error_info *mce_err)
 {
-	long handled = 0;
+	if (mce_in_guest())
+		return 0;
 
 	mce_common_process_ue(regs, mce_err);
 	if (mce_err->ignore_event)
@@ -677,9 +688,10 @@ static long mce_handle_ue_error(struct pt_regs *regs,
 
 	if (ppc_md.mce_check_early_recovery) {
 		if (ppc_md.mce_check_early_recovery(regs))
-			handled = 1;
+			return 1;
 	}
-	return handled;
+
+	return 0;
 }
 
 static long mce_handle_error(struct pt_regs *regs,