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    SubjectRe: [PATCH v3 1/4] iommu/vt-d: Implement domain ops for attach_dev_pasid
    Hi Jason,

    On Tue, 10 May 2022 20:21:21 -0300, Jason Gunthorpe <jgg@nvidia.com> wrote:

    > On Tue, May 10, 2022 at 02:07:01PM -0700, Jacob Pan wrote:
    > > +static int intel_iommu_attach_dev_pasid(struct iommu_domain *domain,
    > > + struct device *dev,
    > > + ioasid_t pasid)
    > > +{
    > > + struct device_domain_info *info = dev_iommu_priv_get(dev);
    > > + struct dmar_domain *dmar_domain = to_dmar_domain(domain);
    > > + struct intel_iommu *iommu = info->iommu;
    > > + unsigned long flags;
    > > + int ret = 0;
    > > +
    > > + if (!sm_supported(iommu) || !info)
    > > + return -ENODEV;
    > > +
    > > + spin_lock_irqsave(&device_domain_lock, flags);
    > > + /*
    > > + * If the same device already has a PASID attached, just
    > > return.
    > > + * DMA layer will return the PASID value to the caller.
    > > + */
    > > + if (pasid != PASID_RID2PASID && info->pasid) {
    >
    > Why check for PASID == 0 like this? Shouldn't pasid == 0 be rejected
    > as an invalid argument?
    Right, I was planning on reuse the attach function for RIDPASID as clean
    up, but didn't include here. Will fix.

    >
    > > + if (info->pasid == pasid)
    > > + ret = 0;
    >
    > Doesn't this need to check that the current domain is the requested
    > domain as well? How can this happen anyhow - isn't it an error to
    > double attach?
    >
    > > diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
    > > index 5af24befc9f1..55845a8c4f4d 100644
    > > +++ b/include/linux/intel-iommu.h
    > > @@ -627,6 +627,7 @@ struct device_domain_info {
    > > struct intel_iommu *iommu; /* IOMMU used by this device */
    > > struct dmar_domain *domain; /* pointer to domain */
    > > struct pasid_table *pasid_table; /* pasid table */
    > > + ioasid_t pasid; /* DMA request with PASID */
    >
    > And this seems wrong - the DMA API is not the only user of
    > attach_dev_pasid, so there should not be any global pasid for the
    > device.
    >
    True but the attach_dev_pasid() op is domain type specific. i.e. DMA API
    has its own attach_dev_pasid which is different than sva domain
    attach_dev_pasid().
    device_domain_info is only used by DMA API.

    > I suspect this should be a counter of # of pasid domains attached so
    > that the special flush logic triggers
    >
    This field is only used for devTLB, so it is per domain-device. struct
    device_domain_info is allocated per device-domain as well. Sorry, I might
    have totally missed your point.

    > And rely on the core code to worry about assigning only one domain per
    > pasid - this should really be a 'set' function.
    >
    Yes, in this set the core code (in dma-iommu.c) only assign one PASID per
    DMA domain type.

    Are you suggesting the dma-iommu API should be called
    iommu_set_dma_pasid instead of iommu_attach_dma_pasid?

    Thanks a lot for the quick review!

    Jacob

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