RE: [PATCH 3/7] iommu/vt-d: Use device_block_translation() in dev_attach error path

[Tian, Kevin]

> From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> Sent: Thursday, November 3, 2022 1:53 PM
> 
> If domain attaching to device fails, the IOMMU driver should bring the
> device to blocking DMA state. The upper layer is expected to recover it
> by attaching a new domain. Use device_block_translation() in the error
> path of dev_attach to make the behavior specific.
> 
> The difference between device_block_translation() and the previous
> dmar_remove_one_dev_info() is that the latter disables PCIe ATS and the
> related PCIe features. This is unnecessary as these features are not per
> domain capabilities, disabling them during domain switching is
> unnecessary.

well, the opposite argument is that when the DMA is blocked what is
the point of enabling ATS/PRI on the device.

btw this change is partial. @attach_dev still calls iommu_enable_pci_caps()
which always tries to enable PCI capabilities w/o checking whether they
have been enabled or not. Then user will hit -EBUSY when related PCI
helpers are called.

another difference worthy of pointing out is that in scalable mode it is
the RID2PASID entry instead of context entry being cleared.