On 2022/6/22 10:56, Ethan Zhao wrote:

在 2022/6/20 16:17, 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 devices will encounter the "DMAR: Setup RID2PASID failed" failure as the pasid entry has already been marke as present. As the result, the IOMMU probing process will be aborted.

This fixes it by skipping RID2PASID setting if the pasid entry has been populated. This works because the IOMMU core ensures that only the same IOMMU domain can be attached to all PCI alias devices at the same time. Therefore the subsequent devices just try to setup the RID2PASID entry with the same domain, which is negligible.

We have two customers reported the issue "DMAR: Setup RID2PASID failed",

Two ASPEED devices locate behind one PCIe-PCI bridge and iommu SM, PT mode is enabled.  Most

Interesting thing is the second device is only used by BIOS, and BIOS left it to OS without shutting down,

and it is useless for OS.

This sounds odd. Isn't this a bug?

Is there practical case multi devices behind PCIe-PCI bridge share the same

PASID entry without any security concern ? these two customer's case is not.

The devices underneath the PCIe-PCI bridge are alias devices of the bridge. PCI alias devices always sit in the same group (the minimal unit that IOMMU guarantees isolation) and can only be attached with a same domain (managed I/O address space). Hence, there's no security concern if they further share the pasid table.

Best regards, baolu