Re: [PATCH v6 10/25] iommufd/viommu: Add IOMMUFD_CMD_HW_QUEUE_ALLOC ioctl

[Baolu Lu]

On 6/16/25 14:47, Nicolin Chen wrote:
> On Mon, Jun 16, 2025 at 02:12:04PM +0800, Baolu Lu wrote:
> > On 6/14/25 15:14, Nicolin Chen wrote:
> > > +	if (!viommu->ops || !viommu->ops->get_hw_queue_size ||
> > > +	    !viommu->ops->hw_queue_init_phys) {
> > > +		rc = -EOPNOTSUPP;
> > > +		goto out_put_viommu;
> > > +	}
> Hmm, here it does abort when !viommu->ops->hw_queue_init_phys ..
>
> > > +	/*
> > > +	 * FIXME once ops->hw_queue_init is introduced, this should check "if
> > > +	 * ops->hw_queue_init_phys". And "access" should be initialized to NULL.
> > > +	 */
> > I just don't follow here. Up until now, only viommu->ops->
> > hw_queue_init_phys has been added, which means the current code only
> > supports hardware queues that access guest memory using physical
> > addresses. The access object is not needed for the other type of
> > hardware queue that uses guest IOVA.
> >
> > So, why not just abort here if ops->hw_queue_init_phys is not supported
> > by the IOMMU driver?
> .. so, it already does.
>
> > Leave other logics to the patches that introduce
> > ops->hw_queue_init? I guess that would make this patch more readible.
> The patch is doing in the way to support the hw_queue_init_phys
> case only. It is just adding some extra FIXMEs as the guideline
> for the future patch adding hw_queue_init op.
>
> I personally don't feel these are confusing. Maybe you can help
> point out what specific wording feels odd here? Maybe "FIXME"s
> should be "TODO"s?

Oh, I probably misunderstood the logic here. For both hw_queue_init and
hw_queue_init_phys, using an access object to pin the pages for hardware
access is necessary, right? My understanding was that pinning pages is
only required for hw_queue_init_phys.

> I could also drop all of these guideline if they are considered
> very unnecessary.
>
> Thanks
> Nicolin

Thanks,
baolu