netdev - Re: [PATCH V1 mlx5-next 11/13] vfio/mlx5: Implement vfio

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Date:   Fri, 15 Oct 2021 16:59:37 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     Yishai Hadas <yishaih@...dia.com>, bhelgaas@...gle.com,
        saeedm@...dia.com, linux-pci@...r.kernel.org, kvm@...r.kernel.org,
        netdev@...r.kernel.org, kuba@...nel.org, leonro@...dia.com,
        kwankhede@...dia.com, mgurtovoy@...dia.com, maorg@...dia.com
Subject: Re: [PATCH V1 mlx5-next 11/13] vfio/mlx5: Implement vfio_pci driver
 for mlx5 devices

On Fri, Oct 15, 2021 at 01:48:20PM -0600, Alex Williamson wrote:
> > +static int mlx5vf_pci_set_device_state(struct mlx5vf_pci_core_device *mvdev,
> > +				       u32 state)
> > +{
> > +	struct mlx5vf_pci_migration_info *vmig = &mvdev->vmig;
> > +	u32 old_state = vmig->vfio_dev_state;
> > +	int ret = 0;
> > +
> > +	if (vfio_is_state_invalid(state) || vfio_is_state_invalid(old_state))
> > +		return -EINVAL;
> 
> if (!VFIO_DEVICE_STATE_VALID(old_state) || !VFIO_DEVICE_STATE_VALID(state))

AFAICT this macro doesn't do what is needed, eg

VFIO_DEVICE_STATE_VALID(0xF000) == true

What Yishai implemented is at least functionally correct - states this
driver does not support are rejected.

> > +	/* Running switches off */
> > +	if ((old_state & VFIO_DEVICE_STATE_RUNNING) !=
> > +	    (state & VFIO_DEVICE_STATE_RUNNING) &&
> 
> ((old_state ^ state) & VFIO_DEVICE_STATE_RUNNING) ?

It is not functionally the same, xor only tells if the bit changed, it
doesn't tell what the current value is, and this needs to know that it
changed to 1

> > +	    (old_state & VFIO_DEVICE_STATE_RUNNING)) {
> > +		ret = mlx5vf_pci_quiesce_device(mvdev);
> > +		if (ret)
> > +			return ret;
> > +		ret = mlx5vf_pci_freeze_device(mvdev);
> > +		if (ret) {
> > +			vmig->vfio_dev_state = VFIO_DEVICE_STATE_INVALID;
> 
> 
> No, the invalid states are specifically unreachable, the uAPI defines
> the error state for this purpose.

Indeed

> The states noted as invalid in the
> uAPI should be considered reserved at this point.  If only there was a
> macro to set an error state... ;)

It should just assign a constant value, there is only one error state.

Jason