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Re: [PATCH v26 05/17] vfio: Add VM state change handler to know state of
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From: |
Cornelia Huck |
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Subject: |
Re: [PATCH v26 05/17] vfio: Add VM state change handler to know state of VM |
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Date: |
Tue, 20 Oct 2020 12:51:05 +0200 |
On Sun, 18 Oct 2020 01:54:56 +0530
Kirti Wankhede <kwankhede@nvidia.com> wrote:
> 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.
> */
Maybe:
"Change the device_state register for device @vbasedev. Bits set in
@mask are preserved, bits set in @value are set, and bits not set in
either @mask or @value are cleared in device_state. If the register
cannot be accessed, the resulting state would be invalid, or the device
enters an error state, an error is returned." ?
>
>
> >>> +{
> >>> + 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.
Hm, now I'm confused. With value == _RUNNING, ~_RUNNING and ~0 as mask
should be equivalent, shouldn't they?
>
>
> >>> + }
> >>> + } 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);
Does this indicate in any way which device was causing problems? (I'm
not sure how visible the error_report would be?)
>
>
> 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)
> >>> {
> >>
> >> (...)
>