Re: [PATCH v11 09/13] iommu/sva: Refactoring iommu_sva_bind/unbind_device()

[Baolu Lu]

On 2022/8/18 21:41, Jason Gunthorpe wrote:
> On Wed, Aug 17, 2022 at 09:20:20AM +0800, Lu Baolu wrote:
> > +
> > +/**
> > + * iommu_sva_bind_device() - Bind a process address space to a device
> > + * @dev: the device
> > + * @mm: the mm to bind, caller must hold a reference to mm_users
> > + *
> > + * Create a bond between device and address space, allowing the device to access
> > + * the mm using the returned PASID. If a bond already exists between @device and
> > + * @mm, it is returned and an additional reference is taken. Caller must call
> > + * iommu_sva_unbind_device() to release each reference.
> > + *
> > + * iommu_dev_enable_feature(dev, IOMMU_DEV_FEAT_SVA) must be called first, to
> > + * initialize the required SVA features.
> > + *
> > + * On error, returns an ERR_PTR value.
> > + */
> > +struct iommu_sva *iommu_sva_bind_device(struct device *dev, struct mm_struct *mm)
> > +{
> > +	struct iommu_domain *domain;
> > +	struct iommu_sva *bond;
>
> This is called handle below, pick one name please

Updated.

> > +	ioasid_t max_pasids;
> > +	int ret;
> > +
> > +	max_pasids = dev->iommu->max_pasids;
> > +	if (!max_pasids)
> > +		return ERR_PTR(-EOPNOTSUPP);
> > +
> > +	/* Allocate mm->pasid if necessary. */
> > +	ret = iommu_sva_alloc_pasid(mm, 1, max_pasids - 1);
> > +	if (ret)
> > +		return ERR_PTR(ret);
> > +
> > +	bond = kzalloc(sizeof(*bond), GFP_KERNEL);
> > +	if (!bond)
> > +		return ERR_PTR(-ENOMEM);
> > +
> > +	mutex_lock(&iommu_sva_lock);
> > +	/* Search for an existing domain. */
> > +	domain = iommu_get_domain_for_dev_pasid(dev, mm->pasid);
> > +	if (domain) {
>
> This isn't safe, or sane. A driver could have attached something to
> this PASID that is not a SVA domain and thus not protected by the
> iommu_sva_lock.
>
> At a minimum you should add a type match to
> iommu_get_domain_for_dev_pasid(), eg to confirm it is a SVA domain and
> do that check under the xa_lock of the pasid xarray.
>
> And then the general idea is that SVA domain attach/detach must hold
> this janky global lock.

Make sense. I will add this logic.

> > +		refcount_inc(&domain->users);
>
> This atomic is always processed under the iommu_sva_lock, so it
> doesn't need to be an atomic anymore.

Will change it to an integer.

> Otherwise this design looks OK to me too

Thank you very much for your suggestions.

Best regards,
baolu