Re: [PATCH v26 07/17] vfio: Register SaveVMHandlers for VFIO device

[Kirti Wankhede <kwankhede@nvidia.com>]

On 9/26/2020 1:50 AM, Alex Williamson wrote:
> On Wed, 23 Sep 2020 04:54:09 +0530
> 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  | 91 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>>   hw/vfio/trace-events |  2 ++
>>   2 files changed, 93 insertions(+)
>>
>> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
>> index f650fe9fc3c8..8e8adaa25779 100644
>> --- a/hw/vfio/migration.c
>> +++ b/hw/vfio/migration.c
>> @@ -8,12 +8,15 @@
>>    */
>>   
>>   #include "qemu/osdep.h"
>> +#include "qemu/main-loop.h"
>> +#include "qemu/cutils.h"
>>   #include <linux/vfio.h>
>>   
>>   #include "sysemu/runstate.h"
>>   #include "hw/vfio/vfio-common.h"
>>   #include "cpu.h"
>>   #include "migration/migration.h"
>> +#include "migration/vmstate.h"
>>   #include "migration/qemu-file.h"
>>   #include "migration/register.h"
>>   #include "migration/blocker.h"
>> @@ -25,6 +28,17 @@
>>   #include "trace.h"
>>   #include "hw/hw.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 inline int vfio_mig_access(VFIODevice *vbasedev, void *val, int count,
>>                                     off_t off, bool iswrite)
>>   {
>> @@ -166,6 +180,65 @@ 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;
>> +
>> +    trace_vfio_save_setup(vbasedev->name);
>> +
>> +    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();
> 
> Please add a comment identifying why the iothread mutex lock is
> necessary here.
> 
>> +        if (ret) {
>> +            error_report("%s: Failed to mmap VFIO migration region %d: %s",
>> +                         vbasedev->name, migration->region.nr,
> 
> We don't support multiple migration regions, is it useful to include
> the region index here?
> 

Ok. Removing region.nr


>> +                         strerror(-ret));
>> +            error_report("%s: Falling back to slow path", vbasedev->name);
>> +        }
>> +    }
>> +
>> +    ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_MASK,
>> +                                   VFIO_DEVICE_STATE_SAVING);
>> +    if (ret) {
>> +        error_report("%s: Failed to set state SAVING", vbasedev->name);
>> +        return ret;
>> +    }
> 
> Again, doesn't match the function semantics that success only means the
> device is in a non-error state, maybe the one that was asked for.
> 

Fixed in patch 05.

>> +
>> +    qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
> 
> What's the overall purpose of writing these markers into the migration
> stream?  vfio_load_state() doesn't do anything with this other than
> validate that the end-of-state immediately follows.  Is this a
> placeholder for something in the future?
> 

Its not placeholder, it is used in vfio_load_state() to determine upto 
what point to loop to fetch data for each state, otherwise how would we 
know when to stop reading data from stream for that VFIO device.

>> +
>> +    ret = qemu_file_get_error(f);
>> +    if (ret) {
>> +        return ret;
>> +    }
>> +
>> +    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;
>> @@ -225,6 +298,8 @@ static int vfio_migration_init(VFIODevice *vbasedev,
>>                                  struct vfio_region_info *info)
>>   {
>>       int ret = -EINVAL;
>> +    char id[256] = "";
>> +    Object *obj;
>>   
>>       if (!vbasedev->ops->vfio_get_object) {
>>           return ret;
>> @@ -241,6 +316,22 @@ static int vfio_migration_init(VFIODevice *vbasedev,
>>           return ret;
>>       }
>>   
>> +    obj = vbasedev->ops->vfio_get_object(vbasedev);
>> +
>> +    if (obj) {
>> +        DeviceState *dev = DEVICE(obj);
>> +        char *oid = vmstate_if_get_id(VMSTATE_IF(dev));
>> +
>> +        if (oid) {
>> +            pstrcpy(id, sizeof(id), oid);
>> +            pstrcat(id, sizeof(id), "/");
>> +            g_free(oid);
>> +        }
>> +    }
> 
> Here's where vfio_migration_init() starts using vfio_get_object() as I
> referenced back on patch 04.  We might as well get the object before
> calling vfio_migration_region_init() and then pass the object.  The
> conditional branch to handle obj is strange here too, it's fatal if
> vfio_migration_region_init() doesn't find an object, why do we handle
> it as optional here?  Also, what is this doing?  Comments would be
> nice...  Thanks,
> 

Changing it as I mentioned in other patch reply.

Thanks.

> Alex
> 
>> +    pstrcat(id, sizeof(id), "vfio");
>> +
>> +    register_savevm_live(id, VMSTATE_INSTANCE_ID_ANY, 1, &savevm_vfio_handlers,
>> +                         vbasedev);
>>       vbasedev->vm_state = qemu_add_vm_change_state_handler(vfio_vmstate_change,
>>                                                             vbasedev);
>>       vbasedev->migration_state.notify = vfio_migration_state_notifier;
>> diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
>> index bcb3fa7314d7..982d8dccb219 100644
>> --- a/hw/vfio/trace-events
>> +++ b/hw/vfio/trace-events
>> @@ -152,3 +152,5 @@ vfio_migration_probe(const char *name, uint32_t index) " (%s) Region %d"
>>   vfio_migration_set_state(const char *name, uint32_t state) " (%s) state %d"
>>   vfio_vmstate_change(const char *name, int running, const char *reason, uint32_t dev_state) " (%s) running %d reason %s device state %d"
>>   vfio_migration_state_notifier(const char *name, const char *state) " (%s) state %s"
>> +vfio_save_setup(const char *name) " (%s)"
>> +vfio_save_cleanup(const char *name) " (%s)"
>