From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jean-Philippe Brucker Subject: Re: [PATCH v4 14/22] iommu: handle page response timeout Date: Mon, 30 Apr 2018 11:58:10 +0100 Message-ID: References: <1523915351-54415-1-git-send-email-jacob.jun.pan@linux.intel.com> <1523915351-54415-15-git-send-email-jacob.jun.pan@linux.intel.com> <20180423153622.GC38106@ostrya.localdomain> <20180425083711.222202e7@jacob-builder> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20180425083711.222202e7@jacob-builder> Content-Language: en-US List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Jacob Pan Cc: Raj Ashok , Greg Kroah-Hartman , Rafael Wysocki , "iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org" , LKML , David Woodhouse List-Id: iommu@lists.linux-foundation.org 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