From 6c3dd24c054a0701169b17be57b611bac8d99b5d Mon Sep 17 00:00:00 2001 From: Nicholas Piggin Date: Thu, 26 Mar 2020 00:29:04 +1000 Subject: [PATCH] ppc/spapr: Improve FWNMI machine check delivery corner case comments Some of the conditions are not as clearly documented as they could be. Also the non-FWNMI case does not need a large comment. Reviewed-by: Greg Kurz Signed-off-by: Nicholas Piggin Message-Id: <20200325142906.221248-3-npiggin@gmail.com> Signed-off-by: David Gibson --- hw/ppc/spapr_events.c | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-) diff --git a/hw/ppc/spapr_events.c b/hw/ppc/spapr_events.c index a4a540f43d..a908c5d0e9 100644 --- a/hw/ppc/spapr_events.c +++ b/hw/ppc/spapr_events.c @@ -860,17 +860,13 @@ void spapr_mce_req_event(PowerPCCPU *cpu, bool recovered) Error *local_err = NULL; if (spapr->fwnmi_machine_check_addr == -1) { - /* - * This implies that we have hit a machine check either when the - * guest has not registered FWNMI (i.e., "ibm,nmi-register" not - * called) or between system reset and "ibm,nmi-register". - * Fall back to the old machine check behavior in such cases. - */ + /* Non-FWNMI case, deliver it like an architected CPU interrupt. */ cs->exception_index = POWERPC_EXCP_MCHECK; ppc_cpu_do_interrupt(cs); return; } + /* Wait for FWNMI interlock. */ while (spapr->fwnmi_machine_check_interlock != -1) { /* * Check whether the same CPU got machine check error @@ -882,8 +878,13 @@ void spapr_mce_req_event(PowerPCCPU *cpu, bool recovered) return; } qemu_cond_wait_iothread(&spapr->fwnmi_machine_check_interlock_cond); - /* Meanwhile if the system is reset, then just return */ if (spapr->fwnmi_machine_check_addr == -1) { + /* + * If the machine was reset while waiting for the interlock, + * abort the delivery. The machine check applies to a context + * that no longer exists, so it wouldn't make sense to deliver + * it now. + */ return; } } @@ -894,7 +895,9 @@ void spapr_mce_req_event(PowerPCCPU *cpu, bool recovered) * We don't want to abort so we let the migration to continue. * In a rare case, the machine check handler will run on the target. * Though this is not preferable, it is better than aborting - * the migration or killing the VM. + * the migration or killing the VM. It is okay to call + * migrate_del_blocker on a blocker that was not added (which the + * nmi-interlock handler would do when it's called after this). */ warn_report("Received a fwnmi while migration was in progress"); } -- 2.11.4.GIT