Re: [Qemu-devel] [PATCH v9 6/6] migration: Include migration support for machine check handling

[Greg Kurz]

On Thu, 6 Jun 2019 13:06:14 +1000
David Gibson <address@hidden> wrote:

> On Wed, May 29, 2019 at 11:10:57AM +0530, Aravinda Prasad wrote:
> > This patch includes migration support for machine check
> > handling. Especially this patch blocks VM migration
> > requests until the machine check error handling is
> > complete as (i) these errors are specific to the source
> > hardware and is irrelevant on the target hardware,
> > (ii) these errors cause data corruption and should
> > be handled before migration.
> > 
> > Signed-off-by: Aravinda Prasad <address@hidden>
> > ---
> >  hw/ppc/spapr.c         |   20 ++++++++++++++++++++
> >  hw/ppc/spapr_events.c  |   17 +++++++++++++++++
> >  hw/ppc/spapr_rtas.c    |    4 ++++
> >  include/hw/ppc/spapr.h |    2 ++
> >  4 files changed, 43 insertions(+)
> > 
> > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > index e8a77636..31c4850 100644
> > --- a/hw/ppc/spapr.c
> > +++ b/hw/ppc/spapr.c
> > @@ -2104,6 +2104,25 @@ static const VMStateDescription vmstate_spapr_dtb = {
> >      },
> >  };
> >  
> > +static bool spapr_fwnmi_needed(void *opaque)
> > +{
> > +    SpaprMachineState *spapr = (SpaprMachineState *)opaque;
> > +
> > +    return (spapr->guest_machine_check_addr == -1) ? 0 : 1;  
> 
> Since we're introducing a PAPR capability to enable this, it would
> actually be better to check that here, rather than the runtime state.
> That leads to less cases and easier to understand semantics for the
> migration stream.
> 

Hmmm... the purpose of needed() VMState callbacks is precisely about
runtime state: the subsection should only be migrated if an MCE is
pending, ie. spapr->guest_machine_check_addr != -1.

> > +}
> > +
> > +static const VMStateDescription vmstate_spapr_machine_check = {
> > +    .name = "spapr_machine_check",
> > +    .version_id = 1,
> > +    .minimum_version_id = 1,
> > +    .needed = spapr_fwnmi_needed,
> > +    .fields = (VMStateField[]) {
> > +        VMSTATE_UINT64(guest_machine_check_addr, SpaprMachineState),
> > +        VMSTATE_INT32(mc_status, SpaprMachineState),
> > +        VMSTATE_END_OF_LIST()
> > +    },
> > +};
> > +
> >  static const VMStateDescription vmstate_spapr = {
> >      .name = "spapr",
> >      .version_id = 3,
> > @@ -2137,6 +2156,7 @@ static const VMStateDescription vmstate_spapr = {
> >          &vmstate_spapr_dtb,
> >          &vmstate_spapr_cap_large_decr,
> >          &vmstate_spapr_cap_ccf_assist,
> > +        &vmstate_spapr_machine_check,
> >          NULL
> >      }
> >  };
> > diff --git a/hw/ppc/spapr_events.c b/hw/ppc/spapr_events.c
> > index 573c0b7..35e21e4 100644
> > --- a/hw/ppc/spapr_events.c
> > +++ b/hw/ppc/spapr_events.c
> > @@ -41,6 +41,7 @@
> >  #include "qemu/bcd.h"
> >  #include "hw/ppc/spapr_ovec.h"
> >  #include <libfdt.h>
> > +#include "migration/blocker.h"
> >  
> >  #define RTAS_LOG_VERSION_MASK                   0xff000000
> >  #define   RTAS_LOG_VERSION_6                    0x06000000
> > @@ -855,6 +856,22 @@ static void spapr_mce_dispatch_elog(PowerPCCPU *cpu, 
> > bool recovered)
> >  void spapr_mce_req_event(PowerPCCPU *cpu, bool recovered)
> >  {
> >      SpaprMachineState *spapr = SPAPR_MACHINE(qdev_get_machine());
> > +    int ret;
> > +    Error *local_err = NULL;
> > +
> > +    error_setg(&spapr->fwnmi_migration_blocker,
> > +            "Live migration not supported during machine check handling");
> > +    ret = migrate_add_blocker(spapr->fwnmi_migration_blocker, &local_err);
> > +    if (ret < 0) {
> > +        /*
> > +         * We don't want to abort and let the migration to continue. In a
> > +         * rare case, the machine check handler will run on the target
> > +         * hardware. Though this is not preferable, it is better than 
> > aborting
> > +         * the migration or killing the VM.
> > +         */
> > +        error_free(spapr->fwnmi_migration_blocker);  
> 
> You should set fwnmi_migration_blocker to NULL here as well.
> 
> As mentioned on an earlier iteration, the migration blocker is the
> same every time.  Couldn't you just create it once and free at final
> teardown, rather than recreating it for every NMI?
> 
> > +        warn_report_err(local_err);
> > +    }
> >  
> >      while (spapr->mc_status != -1) {
> >          /*
> > diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
> > index 91a7ab9..c849223 100644
> > --- a/hw/ppc/spapr_rtas.c
> > +++ b/hw/ppc/spapr_rtas.c
> > @@ -50,6 +50,7 @@
> >  #include "target/ppc/mmu-hash64.h"
> >  #include "target/ppc/mmu-book3s-v3.h"
> >  #include "kvm_ppc.h"
> > +#include "migration/blocker.h"
> >  
> >  static void rtas_display_character(PowerPCCPU *cpu, SpaprMachineState 
> > *spapr,
> >                                     uint32_t token, uint32_t nargs,
> > @@ -404,6 +405,9 @@ static void rtas_ibm_nmi_interlock(PowerPCCPU *cpu,
> >          spapr->mc_status = -1;
> >          qemu_cond_signal(&spapr->mc_delivery_cond);
> >          rtas_st(rets, 0, RTAS_OUT_SUCCESS);
> > +        migrate_del_blocker(spapr->fwnmi_migration_blocker);
> > +        error_free(spapr->fwnmi_migration_blocker);
> > +        spapr->fwnmi_migration_blocker = NULL;
> >      }
> >  }
> >  
> > diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> > index bd75d4b..6c0cfd8 100644
> > --- a/include/hw/ppc/spapr.h
> > +++ b/include/hw/ppc/spapr.h
> > @@ -214,6 +214,8 @@ struct SpaprMachineState {
> >      SpaprCapabilities def, eff, mig;
> >  
> >      unsigned gpu_numa_id;
> > +
> > +    Error *fwnmi_migration_blocker;
> >  };
> >  
> >  #define H_SUCCESS         0
> >   
>

pgppTP_0ffkpa.pgp
Description: OpenPGP digital signature