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
