From: Lu Baolu baolu.lu@linux.intel.com 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@intel.com Reported-by: Ethan Zhao haifeng.zhao@linux.intel.com Cc: stable@vger.kernel.org Signed-off-by: Lu Baolu baolu.lu@linux.intel.com
Looks good.
Reviewed-by: Kevin Tian kevin.tian@intel.com