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
those devices are rare on modern platforms that support VT-d in
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?
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