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

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Date:   Fri, 15 Oct 2021 14:12:01 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Jason Gunthorpe <jgg@...dia.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, 15 Oct 2021 16:59:37 -0300
Jason Gunthorpe <jgg@...dia.com> wrote:

> 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.


if (!VFIO_DEVICE_STATE_VALID(old_state) || !VFIO_DEVICE_STATE_VALID(state)) || (state & ~VFIO_DEVICE_STATE_MASK))

old_state is controlled by the driver and can never have random bits
set, user state should be sanitized to prevent setting undefined bits.


> > > +	/* 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

That's why I inserted my comment after the "it changed" test and not
after the "and the old old value was..." test below.

> > > +	    (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.

Fair enough.  Thanks,

Alex