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

[Tian, Kevin]

> From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> Sent: Thursday, June 23, 2022 2:57 PM
> 
> 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.
> 
> Fixes: ef848b7e5a6a0 ("iommu/vt-d: Setup pasid entry for RID2PASID
> support")
> Reported-by: Chenyi Qiang <chenyi.qiang@xxxxxxxxx>
> Reported-by: Ethan Zhao <haifeng.zhao@xxxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>

Looks good.

Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>