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Subject: Re: [PATCH v16 QEMU 08/16] vfio: Register SaveVMHandlers for VFIO
 device
To: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
References: <1585084154-29461-1-git-send-email-kwankhede@nvidia.com>
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From: Kirti Wankhede <kwankhede@nvidia.com>
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Date: Tue, 5 May 2020 04:50:45 +0530
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On 4/1/2020 11:06 PM, Dr. David Alan Gilbert wrote:
> * Kirti Wankhede (kwankhede@nvidia.com) wrote:
>> Define flags to be used as delimeter in migration file stream.
>> Added .save_setup and .save_cleanup functions. Mapped & unmapped migration
>> region from these functions at source during saving or pre-copy phase.
>> Set VFIO device state depending on VM's state. During live migration, VM is
>> running when .save_setup is called, _SAVING | _RUNNING state is set for VFIO
>> device. During save-restore, VM is paused, _SAVING state is set for VFIO device.
>>
>> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
>> Reviewed-by: Neo Jia <cjia@nvidia.com>
>> ---
>>   hw/vfio/migration.c  | 76 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>>   hw/vfio/trace-events |  2 ++
>>   2 files changed, 78 insertions(+)
>>
>> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
>> index 22ded9d28cf3..033f76526e49 100644
>> --- a/hw/vfio/migration.c
>> +++ b/hw/vfio/migration.c
>> @@ -8,6 +8,7 @@
>>    */
>>   
>>   #include "qemu/osdep.h"
>> +#include "qemu/main-loop.h"
>>   #include <linux/vfio.h>
>>   
>>   #include "sysemu/runstate.h"
>> @@ -24,6 +25,17 @@
>>   #include "pci.h"
>>   #include "trace.h"
>>   
>> +/*
>> + * Flags used as delimiter:
>> + * 0xffffffff => MSB 32-bit all 1s
>> + * 0xef10     => emulated (virtual) function IO
>> + * 0x0000     => 16-bits reserved for flags
>> + */
>> +#define VFIO_MIG_FLAG_END_OF_STATE      (0xffffffffef100001ULL)
>> +#define VFIO_MIG_FLAG_DEV_CONFIG_STATE  (0xffffffffef100002ULL)
>> +#define VFIO_MIG_FLAG_DEV_SETUP_STATE   (0xffffffffef100003ULL)
>> +#define VFIO_MIG_FLAG_DEV_DATA_STATE    (0xffffffffef100004ULL)
>> +
>>   static void vfio_migration_region_exit(VFIODevice *vbasedev)
>>   {
>>       VFIOMigration *migration = vbasedev->migration;
>> @@ -126,6 +138,69 @@ static int vfio_migration_set_state(VFIODevice *vbasedev, uint32_t mask,
>>       return 0;
>>   }
>>   
>> +/* ---------------------------------------------------------------------- */
>> +
>> +static int vfio_save_setup(QEMUFile *f, void *opaque)
>> +{
>> +    VFIODevice *vbasedev = opaque;
>> +    VFIOMigration *migration = vbasedev->migration;
>> +    int ret;
>> +
>> +    qemu_put_be64(f, VFIO_MIG_FLAG_DEV_SETUP_STATE);
>> +
>> +    if (migration->region.mmaps) {
>> +        qemu_mutex_lock_iothread();
>> +        ret = vfio_region_mmap(&migration->region);
>> +        qemu_mutex_unlock_iothread();
>> +        if (ret) {
>> +            error_report("%s: Failed to mmap VFIO migration region %d: %s",
>> +                         vbasedev->name, migration->region.index,
>> +                         strerror(-ret));
>> +            return ret;
>> +        }
>> +    }
>> +
>> +    ret = vfio_migration_set_state(vbasedev, ~0, VFIO_DEVICE_STATE_SAVING);
>> +    if (ret) {
>> +        error_report("%s: Failed to set state SAVING", vbasedev->name);
>> +        return ret;
>> +    }
>> +
>> +    /*
>> +     * Save migration region size. This is used to verify migration region size
>> +     * is greater than or equal to migration region size at destination
>> +     */
>> +    qemu_put_be64(f, migration->region.size);
>> +
>> +    qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
> 
> OK, good, so now we can change that to something else if you want to
> migrate something extra in the future.
> 
>> +    ret = qemu_file_get_error(f);
>> +    if (ret) {
>> +        return ret;
>> +    }
>> +
>> +    trace_vfio_save_setup(vbasedev->name);
> 
> I'd put that trace at the start of the function.
> 
>> +    return 0;
>> +}
>> +
>> +static void vfio_save_cleanup(void *opaque)
>> +{
>> +    VFIODevice *vbasedev = opaque;
>> +    VFIOMigration *migration = vbasedev->migration;
>> +
>> +    if (migration->region.mmaps) {
>> +        vfio_region_unmap(&migration->region);
>> +    }
>> +    trace_vfio_save_cleanup(vbasedev->name);
>> +}
>> +
>> +static SaveVMHandlers savevm_vfio_handlers = {
>> +    .save_setup = vfio_save_setup,
>> +    .save_cleanup = vfio_save_cleanup,
>> +};
>> +
>> +/* ---------------------------------------------------------------------- */
>> +
>>   static void vfio_vmstate_change(void *opaque, int running, RunState state)
>>   {
>>       VFIODevice *vbasedev = opaque;
>> @@ -191,6 +266,7 @@ static int vfio_migration_init(VFIODevice *vbasedev,
>>           return ret;
>>       }
>>   
>> +    register_savevm_live("vfio", -1, 1, &savevm_vfio_handlers, vbasedev);
> 
> That doesn't look right to me;  firstly the -1 should now be
> VMSTATE_INSTANCE_ID_ANY - after the recent change in commit 1df2c9a
> 
> Have you tried this with two vfio devices?

Yes. And it works with multiple vfio devices.

Thanks,
Kirti

> This is quite rare - it's an iterative device that can have
> multiple instances;  if you look at 'ram' for example, all the RAM
> instances are handled inside the save_setup/save for the one instance of
> 'ram'.  I think here you're trying to register an individual vfio
> device, so if you had multiple devices you'd see this called twice.
> 
> So either you need to make vfio_save_* do all of the devices in a loop -
> which feels like a bad idea;  or replace "vfio" in that call by a unique
> device name;  as long as your device has a bus path then you should be
> able to use the same trick vmstate_register_with_alias_id does, and use
> I think,  vmstate_if_get_id(VMSTAETE_IF(vbasedev)).
> 
> but it might take some experimentation since this is an odd use.
> 
>>       vbasedev->vm_state = qemu_add_vm_change_state_handler(vfio_vmstate_change,
>>                                                             vbasedev);
>>   
>> diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
>> index 69503228f20e..4bb43f18f315 100644
>> --- a/hw/vfio/trace-events
>> +++ b/hw/vfio/trace-events
>> @@ -149,3 +149,5 @@ vfio_migration_probe(char *name, uint32_t index) " (%s) Region %d"
>>   vfio_migration_set_state(char *name, uint32_t state) " (%s) state %d"
>>   vfio_vmstate_change(char *name, int running, const char *reason, uint32_t dev_state) " (%s) running %d reason %s device state %d"
>>   vfio_migration_state_notifier(char *name, int state) " (%s) state %d"
>> +vfio_save_setup(char *name) " (%s)"
>> +vfio_save_cleanup(char *name) " (%s)"
>> -- 
>> 2.7.0
>>
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>