On 25/04/18 16:37, Jacob Pan wrote: >> In the other cases (unsupported PRI or rogue guest) then disabling PRI >> using a FAILURE status might be the right thing to do. However, >> assuming the device follows the PCI spec it will stop sending page >> requests once there are as many PPRs in flight as the allocated >> credit. >> > Agreed, here I am not taking any actions. There may be need to drain > in-fly requests.
Right, as long as we first ensure that no new fault is generated (by using a Response Failure). Though in my opinion not taking action might be the safest option :) Another thought: currently the comment in iommu.h says "@IOMMU_FAULT_STATUS_FAILURE: General error. Drop all subsequent faults from this device if possible. This is "Response Failure" in PCI PRI." I wonder if we should simply say "Drop all subsequent faults from the device". Even if the PCI device doesn't properly implement PRI, the IOMMU driver should set a "PRI disabled" bit in the device data that prevents it from from reporting new faults and flooding the queue. Anyway, it's a small detail that could go in a future patch series. >> If there isn't any possibility of memory leak or abusing resources, I >> don't think it's our problem that the guest is excessively slow at >> handling page requests. Setting an upper bound to page request latency >> might do more harm than good. Ensuring that devices respect the number >> of allocated in-flight PPRs is more important in my opinion. >> > How about we have a really long timeout, e.g. 1 min similar to device > invalidate response timeout in ATS spec., just for basic safety and > diagnosis. Optionally, we could have quota in parallel. I agree that for development a timeout is useful. It might be worth adding it as an option to the IOMMU module instead of a define. Perhaps a number of seconds, 10 being the default and 0 disabling the timeout? Otherwise we would probably end up with a succession of patches incrementing the timeout by arbitrary values, if people find it inconvenient. Thanks, Jean _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
