Re: [PATCH v17 6/7] migration: Include migration support for machine check handling

[Ganesh <ganeshgr@linux.ibm.com>]

On 11/19/19 8:15 AM, David Gibson wrote:
> On Thu, Oct 24, 2019 at 01:13:06PM +0530, Ganesh Goudar wrote:
>> From: Aravinda Prasad <arawinda.p@gmail.com>
>>
>> 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 these errors are specific to the source
>> hardware and is irrelevant on the target hardware.
>>
>> [Do not set FWNMI cap in post_load, now its done in .apply hook]
>> Signed-off-by: Ganesh Goudar <ganeshgr@linux.ibm.com>
>> Signed-off-by: Aravinda Prasad <arawinda.p@gmail.com>
>> ---
>>   hw/ppc/spapr.c         | 41 +++++++++++++++++++++++++++++++++++++++++
>>   hw/ppc/spapr_events.c  | 16 +++++++++++++++-
>>   hw/ppc/spapr_rtas.c    |  2 ++
>>   include/hw/ppc/spapr.h |  2 ++
>>   4 files changed, 60 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
>> index 346ec5ba6c..e0d0f95ec0 100644
>> --- a/hw/ppc/spapr.c
>> +++ b/hw/ppc/spapr.c
>> @@ -46,6 +46,7 @@
>>   #include "migration/qemu-file-types.h"
>>   #include "migration/global_state.h"
>>   #include "migration/register.h"
>> +#include "migration/blocker.h"
>>   #include "mmu-hash64.h"
>>   #include "mmu-book3s-v3.h"
>>   #include "cpu-models.h"
>> @@ -1751,6 +1752,8 @@ static void spapr_machine_reset(MachineState *machine)
>>   
>>       /* Signal all vCPUs waiting on this condition */
>>       qemu_cond_broadcast(&spapr->mc_delivery_cond);
>> +
>> +    migrate_del_blocker(spapr->fwnmi_migration_blocker);
>>   }
>>   
>>   static void spapr_create_nvram(SpaprMachineState *spapr)
>> @@ -2041,6 +2044,43 @@ static const VMStateDescription vmstate_spapr_dtb = {
>>       },
>>   };
>>   
>> +static bool spapr_fwnmi_needed(void *opaque)
>> +{
>> +    SpaprMachineState *spapr = (SpaprMachineState *)opaque;
>> +
>> +    return spapr->guest_machine_check_addr != -1;
>> +}
>> +
>> +static int spapr_fwnmi_pre_save(void *opaque)
>> +{
>> +    SpaprMachineState *spapr = (SpaprMachineState *)opaque;
>> +
>> +    /*
>> +     * With -only-migratable QEMU option, we cannot block migration.
>> +     * Hence check if machine check handling is in progress and print
>> +     * a warning message.
>> +     */
> IIUC the logic below this could also occur in the case where the fwnmi
> event occurs after a migration has started, but before it completes,
> not just with -only-migratable.  Is that correct?
Yes
>
>> +    if (spapr->mc_status != -1) {
>> +        warn_report("A machine check is being handled during migration. The"
>> +                "handler may run and log hardware error on the destination");
>> +    }
>> +
>> +    return 0;
>> +}
>> +
>> +static const VMStateDescription vmstate_spapr_machine_check = {
>> +    .name = "spapr_machine_check",
>> +    .version_id = 1,
>> +    .minimum_version_id = 1,
>> +    .needed = spapr_fwnmi_needed,
>> +    .pre_save = spapr_fwnmi_pre_save,
>> +    .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,
>> @@ -2075,6 +2115,7 @@ static const VMStateDescription vmstate_spapr = {
>>           &vmstate_spapr_cap_large_decr,
>>           &vmstate_spapr_cap_ccf_assist,
>>           &vmstate_spapr_cap_fwnmi,
>> +        &vmstate_spapr_machine_check,
>>           NULL
>>       }
>>   };
>> diff --git a/hw/ppc/spapr_events.c b/hw/ppc/spapr_events.c
>> index db44e09154..30d9371c88 100644
>> --- a/hw/ppc/spapr_events.c
>> +++ b/hw/ppc/spapr_events.c
>> @@ -43,6 +43,7 @@
>>   #include "qemu/main-loop.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
>> @@ -842,6 +843,8 @@ void spapr_mce_req_event(PowerPCCPU *cpu, bool recovered)
>>   {
>>       SpaprMachineState *spapr = SPAPR_MACHINE(qdev_get_machine());
>>       CPUState *cs = CPU(cpu);
>> +    int ret;
>> +    Error *local_err = NULL;
>>   
>>       if (spapr->guest_machine_check_addr == -1) {
>>           /*
>> @@ -871,8 +874,19 @@ void spapr_mce_req_event(PowerPCCPU *cpu, bool recovered)
>>               return;
>>           }
>>       }
>> -    spapr->mc_status = cpu->vcpu_id;
>>   
>> +    ret = migrate_add_blocker(spapr->fwnmi_migration_blocker, &local_err);
>> +    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.
>> +         */
>> +        warn_report_err(local_err);
> I suspect the error message in local_err won't be particularly
> meaningful on its own.  Perhaps you need to add a prefix to clarify
> that the problem is you've received a fwnmi after migration has
> commenced?
ok
>
>> +    }
>> +
>> +    spapr->mc_status = cpu->vcpu_id;
>>       spapr_mce_dispatch_elog(cpu, recovered);
>>   }
>>   
>> diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
>> index 0328b1f341..c78d96ee7e 100644
>> --- a/hw/ppc/spapr_rtas.c
>> +++ b/hw/ppc/spapr_rtas.c
>> @@ -50,6 +50,7 @@
>>   #include "hw/ppc/fdt.h"
>>   #include "target/ppc/mmu-hash64.h"
>>   #include "target/ppc/mmu-book3s-v3.h"
>> +#include "migration/blocker.h"
>>   
>>   static void rtas_display_character(PowerPCCPU *cpu, SpaprMachineState *spapr,
>>                                      uint32_t token, uint32_t nargs,
>> @@ -446,6 +447,7 @@ static void rtas_ibm_nmi_interlock(PowerPCCPU *cpu,
>>        */
>>       spapr->mc_status = -1;
>>       qemu_cond_signal(&spapr->mc_delivery_cond);
>> +    migrate_del_blocker(spapr->fwnmi_migration_blocker);
> Oh... damn.  I suggested using a static fwnmi_migration_blocker
> instance, but I just realized there's a problem with it.
>
> If we do receive multiple fwnmi events on different cpus at roughly
> the same time, this will break: I think we'll try to add the same
> migration blocker instance multiple times, which won't be good.  Even
> if that doesn't do anything *too* bad, then we'll unblock the
> migration on the first interlock, rather than waiting for all pending
> fwnmi events to complete.
Ok, not sure how to handle this, ill look into it.
>
>>       rtas_st(rets, 0, RTAS_OUT_SUCCESS);
>>   }
>>   
>> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
>> index 86f0fc8fdd..290abd6328 100644
>> --- a/include/hw/ppc/spapr.h
>> +++ b/include/hw/ppc/spapr.h
>> @@ -215,6 +215,8 @@ struct SpaprMachineState {
>>   
>>       unsigned gpu_numa_id;
>>       SpaprTpmProxy *tpm_proxy;
>> +
>> +    Error *fwnmi_migration_blocker;
>>   };
>>   
>>   #define H_SUCCESS         0