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

[Ethan Zhao]

在 2022/6/24 14:54, Baolu Lu 写道:
> 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?
Sure !
> Best regards,
> baolu

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