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

[Greg Kurz]

On Thu, 6 Jun 2019 16:45:30 +0530
Aravinda Prasad <address@hidden> wrote:

> On Thursday 06 June 2019 11:36 AM, Greg Kurz wrote:
> > 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.  
> 
> spapr->guest_machine_check_addr is set when fwnmi is registered. Hence
> an MCE might not be pending if it is set.
> 

Oops sorry, got confused... should have written "if the guest has
registered FWNMI", but the idea is the same. We only need to migrate
the subsection if the state is different from reset. This is the way
needed() callbacks are generally implemented.

> I am fine with both the approaches (checking for
> guest_machine_check_addr or for SPAPR_CAP_FWNMI_MCE).
> 

I would find ackward to migrate this always for new machine types,
even if the guest doesn't register FWNMI...

> Regards,
> Aravinda
> 
> >   
> >>> +}
> >>> +
> >>> +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
> >>>     
> >>  
> >   
>