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

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Date:   Fri, 15 Oct 2021 17:16:54 -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 02:12:01PM -0600, Alex Williamson wrote:
> 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.

In that instance let's just write

old_state != VFIO_DEVICE_STATE_ERROR

?

I'm happy to see some device specific mask selecting the bits it
supports.

> > > > +	/* 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.

Oh, I see, it was not clear to me

Thanks,
Jason