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

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

On 12/6/19 6:52 AM, David Gibson wrote:
> On Thu, Dec 05, 2019 at 10:39:29AM +0530, Ganesh wrote:
>> 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
> Ok, please update the comment accordingly.
sure
>
>>>> +    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.
> Well, you can do it by reverting to the old approach of dynamically
> creating the Error object before adding it as blocker (and freeing it
> when the blocker is removed).  It's a bit ugly, but it will suffice.
Sure, Thanks
>
>>>>        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