Re: [PATCH v3 1/1] iommu/vt-d: Fix RID2PASID setup/teardown failure

[Baolu Lu]

On 2022/6/24 14:02, Ethan Zhao wrote:
> 在 2022/6/23 14:57, Lu Baolu 写道:
> > The IOMMU driver shares the pasid table for PCI alias devices. When the
> > RID2PASID entry of the shared pasid table has been filled by the first
> > device, the subsequent device will encounter the "DMAR: Setup RID2PASID
> > failed" failure as the pasid entry has already been marked as present.
> > As the result, the IOMMU probing process will be aborted.
> >
> > On the contrary, when any alias device is hot-removed from the system,
> > for example, by writing to /sys/bus/pci/devices/.../remove, the shared
> > RID2PASID will be cleared without any notifications to other devices.
> > As the result, any DMAs from those rest devices are blocked.
> >
> > Sharing pasid table among PCI alias devices could save two memory pages
> > for devices underneath the PCIe-to-PCI bridges. Anyway, considering that
> > those devices are rare on modern platforms that support VT-d in scalable
> > mode and the saved memory is negligible, it's reasonable to remove this
> > part of immature code to make the driver feasible and stable.
> In my understanding, thus cleanning will make the pasid table become
> per-dev datastructure whatever the dev is pci-alias or not, and the
> pasid_pte_is_present(pte)will only check against every pci-alias' own
> private pasid table,the setup stagewouldn't break, so does the
> detach/release path, and little value to code otherreference counter
> like complex implenmataion, looks good to me !

Thanks! Can I add a Reviewd-by from you?

Best regards,
baolu