powerpc/book3s: Fix guest MC delivery mechanism to avoid soft lockups in guest.

Currently we forward MCEs to guest which have been recovered by guest.
And for unhandled errors we do not deliver the MCE to guest. It looks like
with no support of FWNMI in qemu, guest just panics whenever we deliver the
recovered MCEs to guest. Also, the existig code used to return to host for
unhandled errors which was casuing guest to hang with soft lockups inside
guest and makes it difficult to recover guest instance.

This patch now forwards all fatal MCEs to guest causing guest to crash/panic.
And, for recovered errors we just go back to normal functioning of guest
instead of returning to host. This fixes soft lockup issues in guest.
This patch also fixes an issue where guest MCE events were not logged to
host console.

Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 7 insertions, 8 deletions

diff --git a/arch/powerpc/kvm/book3s_hv_ras.c b/arch/powerpc/kvm/book3s_hv_ras.c
index 768a9f977c00..3a5c568b1e89 100644
--- a/arch/powerpc/kvm/book3s_hv_ras.c
+++ b/arch/powerpc/kvm/book3s_hv_ras.c
@@ -113,10 +113,8 @@ static long kvmppc_realmode_mc_power7(struct kvm_vcpu *vcpu)
 	 * We assume that if the condition is recovered then linux host
 	 * will have generated an error log event that we will pick
 	 * up and log later.
-	 * Don't release mce event now. In case if condition is not
-	 * recovered we do guest exit and go back to linux host machine
-	 * check handler. Hence we need make sure that current mce event
-	 * is available for linux host to consume.
+	 * Don't release mce event now. We will queue up the event so that
+	 * we can log the MCE event info on host console.
 	 */
 	if (!get_mce_event(&mce_evt, MCE_EVENT_DONTRELEASE))
 		goto out;
@@ -128,11 +126,12 @@ static long kvmppc_realmode_mc_power7(struct kvm_vcpu *vcpu)
 
 out:
 	/*
-	 * If we have handled the error, then release the mce event because
-	 * we will be delivering machine check to guest.
+	 * We are now going enter guest either through machine check
+	 * interrupt (for unhandled errors) or will continue from
+	 * current HSRR0 (for handled errors) in guest. Hence
+	 * queue up the event so that we can log it from host console later.
 	 */
-	if (handled)
-		release_mce_event();
+	machine_check_queue_event();
 
 	return handled;
 }