Commit 6c3dd24c authored by Nicholas Piggin's avatar Nicholas Piggin Committed by David Gibson
Browse files

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: default avatarGreg Kurz <groug@kaod.org>
Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
Message-Id: <20200325142906.221248-3-npiggin@gmail.com>
Signed-off-by: default avatarDavid Gibson <david@gibson.dropbear.id.au>
parent ec010c00

hw/ppc/spapr_events.c

+11 −8
Original line number Diff line number Diff line
@@ -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");

    }