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Subject: Re: [PATCH v26 05/17] vfio: Add VM state change handler to know state
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To: "Dr. David Alan Gilbert" <dgilbert@redhat.com>, Cornelia Huck
 <cohuck@redhat.com>
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From: Kirti Wankhede <kwankhede@nvidia.com>
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Date: Sun, 18 Oct 2020 01:54:56 +0530
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On 9/29/2020 4:33 PM, Dr. David Alan Gilbert wrote:
> * Cornelia Huck (cohuck@redhat.com) wrote:
>> On Wed, 23 Sep 2020 04:54:07 +0530
>> Kirti Wankhede <kwankhede@nvidia.com> wrote:
>>
>>> VM state change handler gets called on change in VM's state. This is used to set
>>> VFIO device state to _RUNNING.
>>>
>>> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
>>> Reviewed-by: Neo Jia <cjia@nvidia.com>
>>> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
>>> ---
>>>   hw/vfio/migration.c           | 136 ++++++++++++++++++++++++++++++++++++++++++
>>>   hw/vfio/trace-events          |   3 +-
>>>   include/hw/vfio/vfio-common.h |   4 ++
>>>   3 files changed, 142 insertions(+), 1 deletion(-)
>>>
>>
>> (...)
>>
>>> +static int vfio_migration_set_state(VFIODevice *vbasedev, uint32_t mask,
>>> +                                    uint32_t value)
>>
>> I think I've mentioned that before, but this function could really
>> benefit from a comment what mask and value mean.
>>

Adding a comment as:

/*
  *  Write device_state field to inform the vendor driver about the 
device state
  *  to be transitioned to.
  *  vbasedev: VFIO device
  *  mask : bits set in the mask are preserved in device_state
  *  value: bits set in the value are set in device_state
  *  Remaining bits in device_state are cleared.
  */


>>> +{
>>> +    VFIOMigration *migration = vbasedev->migration;
>>> +    VFIORegion *region = &migration->region;
>>> +    off_t dev_state_off = region->fd_offset +
>>> +                      offsetof(struct vfio_device_migration_info, device_state);
>>> +    uint32_t device_state;
>>> +    int ret;
>>> +
>>> +    ret = vfio_mig_read(vbasedev, &device_state, sizeof(device_state),
>>> +                        dev_state_off);
>>> +    if (ret < 0) {
>>> +        return ret;
>>> +    }
>>> +
>>> +    device_state = (device_state & mask) | value;
>>> +
>>> +    if (!VFIO_DEVICE_STATE_VALID(device_state)) {
>>> +        return -EINVAL;
>>> +    }
>>> +
>>> +    ret = vfio_mig_write(vbasedev, &device_state, sizeof(device_state),
>>> +                         dev_state_off);
>>> +    if (ret < 0) {
>>> +        ret = vfio_mig_read(vbasedev, &device_state, sizeof(device_state),
>>> +                          dev_state_off);
>>> +        if (ret < 0) {
>>> +            return ret;
>>> +        }
>>> +
>>> +        if (VFIO_DEVICE_STATE_IS_ERROR(device_state)) {
>>> +            hw_error("%s: Device is in error state 0x%x",
>>> +                     vbasedev->name, device_state);
>>> +            return -EFAULT;
>>
>> Is -EFAULT a good return value here? Maybe -EIO?
>>

Ok. Changing to -EIO.

>>> +        }
>>> +    }
>>> +
>>> +    vbasedev->device_state = device_state;
>>> +    trace_vfio_migration_set_state(vbasedev->name, device_state);
>>> +    return 0;
>>> +}
>>> +
>>> +static void vfio_vmstate_change(void *opaque, int running, RunState state)
>>> +{
>>> +    VFIODevice *vbasedev = opaque;
>>> +
>>> +    if ((vbasedev->vm_running != running)) {
>>> +        int ret;
>>> +        uint32_t value = 0, mask = 0;
>>> +
>>> +        if (running) {
>>> +            value = VFIO_DEVICE_STATE_RUNNING;
>>> +            if (vbasedev->device_state & VFIO_DEVICE_STATE_RESUMING) {
>>> +                mask = ~VFIO_DEVICE_STATE_RESUMING;
>>
>> I've been staring at this for some time and I think that the desired
>> result is
>> - set _RUNNING
>> - if _RESUMING was set, clear it, but leave the other bits intact

Upto here, you're correct.

>> - if _RESUMING was not set, clear everything previously set
>> This would really benefit from a comment (or am I the only one
>> struggling here?)
>>

Here mask should be ~0. Correcting it.


>>> +            }
>>> +        } else {
>>> +            mask = ~VFIO_DEVICE_STATE_RUNNING;
>>> +        }
>>> +
>>> +        ret = vfio_migration_set_state(vbasedev, mask, value);
>>> +        if (ret) {
>>> +            /*
>>> +             * vm_state_notify() doesn't support reporting failure. If such
>>> +             * error reporting support added in furure, migration should be
>>> +             * aborted.
>>
>>
>> "We should abort the migration in this case, but vm_state_notify()
>> currently does not support reporting failures."
>>
>> ?
>>

Ok. Updating comment as suggested here.

>> Can/should we mark the failing device in some way?
> 
> I think you can call qemu_file_set_error on the migration stream to
> force an error.
> 

It should be as below, right?
qemu_file_set_error(migrate_get_current()->to_dst_file, ret);


Thanks,
Kirti

> Dave
> 
>>> +             */
>>> +            error_report("%s: Failed to set device state 0x%x",
>>> +                         vbasedev->name, value & mask);
>>> +        }
>>> +        vbasedev->vm_running = running;
>>> +        trace_vfio_vmstate_change(vbasedev->name, running, RunState_str(state),
>>> +                                  value & mask);
>>> +    }
>>> +}
>>> +
>>>   static int vfio_migration_init(VFIODevice *vbasedev,
>>>                                  struct vfio_region_info *info)
>>>   {
>>
>> (...)