Re: [PATCH v1 02/20] iommu: Introduce a test_dev domain op and an internal helper

[Jason Gunthorpe <jgg@nvidia.com>]

On Mon, Oct 20, 2025 at 11:51:49AM -0700, Nicolin Chen wrote:
> On Mon, Oct 20, 2025 at 01:27:36PM -0300, Jason Gunthorpe wrote:
> > On Sun, Oct 12, 2025 at 05:04:59PM -0700, Nicolin Chen wrote:
> > 
> > > And keep them within the group->mutex, so drivers can simply move all the
> > > sanity and compatibility tests from their attach_dev callbacks to the new
> > > test_dev callbacks without concerning about a race condition.
> > 
> > I'm not sure about this.. For the problem we are trying to solve this
> > would be racy as the test would be done and the group mutex
> > unlocked. Then later it will be re-tested and attached.
> 
> Oh right, we'll have to retest in iommu_dev_reset_done(). I missed
> that.
> 
> > > @@ -751,6 +760,8 @@ struct iommu_ops {
> > >   * @free: Release the domain after use.
> > >   */
> > >  struct iommu_domain_ops {
> > > +	int (*test_dev)(struct iommu_domain *domain, struct device *dev,
> > > +			ioasid_t pasid, struct iommu_domain *old);
> > 
> > Because of the starting remark I'm skeptical that old should be
> > included here.
> 
> Hmm, the followings functions sanitizes "old":
>  - qcom_iommu_identity_attach() drivers/iommu/arm/arm-smmu/qcom_iommu.c

That shouldn't be copied over to test??

        if (domain == identity_domain || !domain)
                return 0;

That is just optimizing away the attach if it has nothing to do

        qcom_domain = to_qcom_iommu_domain(domain);
        if (WARN_ON(!qcom_domain->iommu))
                return -EINVAL;

That can't never happen

>  - iommu_sva_set_dev_pasid() in drivers/iommu/amd/pasid.c

Its broken, you are not required by API to detach a domain before
setting a new one. Keep it in attach, hope someone fixes this driver
someday.

Jason