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

[Aravinda Prasad]

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.

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

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
>>>   
>>
> 

-- 
Regards,
Aravinda