Public bug reported: Description: s390x/pci: Honor vfio DMA limiting Symptom: vfio-pci device on s390 enters error state Problem: Kernel commit 492855939bdb added a limit to the number of concurrent DMA requests for a vfio container. However, lazy unmapping in s390 can in fact cause quite a large number of outstanding DMA requests to build up prior to being purged, potentially the entire guest DMA space. This results in unexpected errors seen in qemu such as 'VFIO_MAP_DMA failed: No space left on device' Solution: The solution requires a change to both kernel and qemu - For qemu, add functionality to get the number of allowable DMA DMA requests via the VFIO_IOMMU_GET_INFO ioctl and then ensure that the guest is told to refresh mappings before exceeding the vfio limit. Reproduction: Put a vfio-pci device on s390 under I/O load
This QEMU issue is related to the kernel issue in launchpad bug #1907421. Backport patches have been attached for a subset of the required patches for this fix... The backports required boiled down to 3 major reasons: 1) For the header sync, I suspect you only want the minimal set of changes needed 2) There is a missing upstream commit (408b55db8be3) that re-organizes the location of 2 s390-pci header files, causing conflicts 3) Adjustments had to be made due to the QEMU build system change (meson) I initially performed the backport against 4.2/focal-devel; the same patches and process will also apply cleanly to 5.0/groovy-devel. There should be nothing required for hirsute as everything is already in upstream QEMU 5.2. In summary: 53ba2eee52bf: Backport as patch 0001. Rather than doing a full header sync, update ONLY the header change needed for the DMA fix. See attached patch 0001. 3ab7a0b40d4b: cherry-pick works 7486a62845b1: cherry-pick works cd7498d07fbb: Backport as patch 0004. This upstream commit added a new part using meson, which does not exist in 5.0. 37fa32de7073: Backport as patch 0005. This was mainly due to conflicts with a missing patch that relocated some include files. 77280d33bc9c: Backport as patch 0006. This was due to different build system + CONFIG_DEVICES doesn't exist. As such, I have attached patches 0001, 0004, 0005 and 0006. Please cherry pick for patches 0002 and 0003. To verify, I applied the patches provided and cherry-picks against both focal-devel and groovy-devel. In each case, for the host system I used the groovy kernel Frank provided in launchpad bug #1907421 which includes the kernel portion of this fix -- using these together, I verified that the DMA limit is being read in and honored appropriately by QEMU, and I can no longer trigger an overrun of the DMA space when a guest pushes heavy data transfer via PCI (no errors in log, no transfer stalls). Also, as related to the last patch of the set, I further verified that no build errors are encountered when configured with --without-default- devices. ** Affects: linux (Ubuntu) Importance: Undecided Assignee: Skipper Bug Screeners (skipper-screen-team) Status: New ** Tags: architecture-s39064 bugnameltc-190223 severity-high targetmilestone-inin--- ** Tags added: architecture-s39064 bugnameltc-190223 severity-high targetmilestone-inin--- -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1913395 Title: [UBUNTU 21.04] qemu s390x/pci: Honor vfio DMA limiting To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1913395/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs