Re: [Qemu-devel] [Qemu-ppc] [PATCH v8 6/6] migration: Block migration while handling machine check

[Aravinda Prasad <aravinda@linux.vnet.ibm.com>]

On Friday 10 May 2019 12:21 PM, David Gibson wrote:
> On Mon, Apr 22, 2019 at 12:33:45PM +0530, Aravinda Prasad wrote:
>> Block 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 <aravinda@linux.vnet.ibm.com>
>> ---
>>  hw/ppc/spapr_events.c  |   17 +++++++++++++++++
>>  hw/ppc/spapr_rtas.c    |    4 ++++
>>  include/hw/ppc/spapr.h |    3 +++
>>  3 files changed, 24 insertions(+)
>>
>> diff --git a/hw/ppc/spapr_events.c b/hw/ppc/spapr_events.c
>> index 4032db0..45b990c 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
>> @@ -864,6 +865,22 @@ 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->migration_blocker,
>> +            "Live migration not supported during machine check handling");
>> +    ret = migrate_add_blocker(spapr->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->migration_blocker);
>> +        fprintf(stderr, "Warning: Machine check during VM migration\n");
> 
> Use report_err() instead of a raw fprintf().
> 
>> +    }
>>  
>>      while (spapr->mc_status != -1) {
>>          /*
>> diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
>> index 997cf19..1229a0e 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,
>> @@ -396,6 +397,9 @@ 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->migration_blocker);
>> +        error_free(spapr->migration_blocker);
>> +        spapr->migration_blocker = NULL;
>>      }
>>  }
>>  
>> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
>> index 9d16ad1..dda5fd2 100644
>> --- a/include/hw/ppc/spapr.h
>> +++ b/include/hw/ppc/spapr.h
>> @@ -10,6 +10,7 @@
>>  #include "hw/ppc/spapr_irq.h"
>>  #include "hw/ppc/spapr_xive.h"  /* For SpaprXive */
>>  #include "hw/ppc/xics.h"        /* For ICSState */
>> +#include "qapi/error.h"
>>  
>>  struct SpaprVioBus;
>>  struct SpaprPhbState;
>> @@ -213,6 +214,8 @@ struct SpaprMachineState {
>>      SpaprCapabilities def, eff, mig;
>>  
>>      unsigned gpu_numa_id;
>> +
>> +    Error *migration_blocker;
> 
> This name doesn't seem good - it's specific to fwnmi, not any other
> migration blockers we might have in future.  It also always contains
> the same string - could you just initialize that in a global and just
> do the migrate_add_blocker() / migrate_del_blocker() instead?

I retained it in SpaprMachineState instead of a global variable because
we add the blocker in spapr_events.c and delete it in spapr_rtas.c

But I have renamed it to fwnmi_migration_blocker.

Regards,
Aravinda

> 
>>  };
>>  
>>  #define H_SUCCESS         0
>>
> 

-- 
Regards,
Aravinda