Re: [PATCH v5 06/13] iommufd: Allow pt_id to carry viommu_id for IOMMU_HWPT_ALLOC

[Nicolin Chen <nicolinc@xxxxxxxxxx>]

On Mon, Oct 28, 2024 at 10:03:09AM -0300, Jason Gunthorpe wrote:
> On Mon, Oct 28, 2024 at 11:24:10AM +0800, Zhangfei Gao wrote:
> 
> > > +/**
> > > + * iommufd_viommu_alloc_hwpt_nested() - Get a hwpt_nested for a vIOMMU
> > > + * @viommu: vIOMMU ojbect to associate the hwpt_nested/domain with
> > > + * @user_data: user_data pointer. Must be valid
> > > + *
> > > + * Allocate a new IOMMU_DOMAIN_NESTED for a vIOMMU and return it as a NESTED
> > > + * hw_pagetable.
> > > + */
> > > +static struct iommufd_hwpt_nested *
> > > +iommufd_viommu_alloc_hwpt_nested(struct iommufd_viommu *viommu, u32 flags,
> > > +                                const struct iommu_user_data *user_data)
> > > +{
> > > +       struct iommufd_hwpt_nested *hwpt_nested;
> > > +       struct iommufd_hw_pagetable *hwpt;
> > > +       int rc;
> > > +
> > > +       if (flags)
> > > +               return ERR_PTR(-EOPNOTSUPP);
> > 
> > This check should be removed.
> > 
> > When a user page fault is required, IOMMU_HWPT_FAULT_ID_VALID is set.
> > if (cmd->flags & IOMMU_HWPT_FAULT_ID_VALID) {
> 
> It can't just be removed..
> 
> I suspect that IOMMU_HWPT_FAULT_ID_VALID should not be set on the
> nested domain but on the parent?

By giving another look,

In iommufd_hwpt_paging_alloc(), we reject IOMMU_HWPT_FAULT_ID_VALID:
	const u32 valid_flags = IOMMU_HWPT_ALLOC_NEST_PARENT |
				IOMMU_HWPT_ALLOC_DIRTY_TRACKING;
	...
	if (flags & ~valid_flags)
		return ERR_PTR(-EOPNOTSUPP);

In iommufd_hwpt_nested_alloc(), we mask the flag away:
	if ((flags & ~IOMMU_HWPT_FAULT_ID_VALID) ||
	    !user_data->len || !ops->domain_alloc_user)
		return ERR_PTR(-EOPNOTSUPP);
	...
	hwpt->domain = ops->domain_alloc_user(idev->dev,
					      flags & ~IOMMU_HWPT_FAULT_ID_VALID,
					      parent->common.domain, user_data);

Then, in the common function it has a section of
	if (cmd->flags & IOMMU_HWPT_FAULT_ID_VALID) {
	...

It seems that this IOMMU_HWPT_FAULT_ID_VALID is for nested domains?

So, aligning with that, here we need:
	if ((flags & ~IOMMU_HWPT_FAULT_ID_VALID) || !user_data->len)
		return ERR_PTR(-EOPNOTSUPP);

And looks like we don't have some detailed documentation w.r.t.
this flag and Fault Queue. We'd likely need to update the uAPI
doc, prior to (or along with) the Part-3 vIRQ series.

Thanks
Nicolin