On Tue, Jul 20, 2021 at 02:53:55PM +0200, Markus Armbruster wrote:
> spapr_mce_req_event() makes an effort to prevent migration from
> degrading the reporting of FWNMIs. It adds a migration blocker when
> it receives one, and deletes it when it's done handling it. This is a
> best effort.
>
> Commit 2500fb423a "migration: Include migration support for machine
> check handling" tried to explain this in a comment. Rewrite the
> comment for clarity, and reposition it to make it clear it applies to
> all failure modes, not just "migration already in progress".
>
> Cc: David Gibson <david@gibson.dropbear.id.au>
> Cc: Aravinda Prasad <arawinda.p@gmail.com>
> Cc: Ganesh Goudar <ganeshgr@linux.ibm.com>
> Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
> ---
> hw/ppc/spapr_events.c | 17 +++++++++--------
> 1 file changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/hw/ppc/spapr_events.c b/hw/ppc/spapr_events.c
> index a8f2cc6bdc..7d6876f12d 100644
> --- a/hw/ppc/spapr_events.c
> +++ b/hw/ppc/spapr_events.c
> @@ -911,16 +911,17 @@ void spapr_mce_req_event(PowerPCCPU *cpu, bool recovered)
> }
> }
>
> + /*
> + * Try to block migration while FWNMI is being handled, so the
> + * machine check handler runs where the information passed to it
> + * actually makes sense. This shouldn't actually block migration,
> + * only delay it slightly, assuming migration is retried. If the
> + * attempt to block fails, carry on. Unfortunately, it always
> + * fails when running with -only-migrate. A proper interface to
> + * delay migration completion for a bit could avoid that.
> + */
> ret = migrate_add_blocker(spapr->fwnmi_migration_blocker, NULL);
> if (ret == -EBUSY) {
> - /*
> - * 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. 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");
> }
>
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson