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envelope-from=steven.sistare@oracle.com; helo=mx0a-00069f02.pphosted.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 2/28/2025 1:13 PM, Steven Sistare wrote: > On 2/28/2025 12:39 PM, Andrey Drobyshev wrote: >> Hi all, >> >> We've been experimenting with cpr-transfer migration mode recently and >> have discovered the following issue with the guest QXL driver: >> >> Run migration source: >>> EMULATOR=/path/to/emulator >>> ROOTFS=/path/to/image >>> QMPSOCK=/var/run/alma8qmp-src.sock >>> >>> $EMULATOR -enable-kvm \ >>>      -machine q35 \ >>>      -cpu host -smp 2 -m 2G \ >>>      -object memory-backend-file,id=ram0,size=2G,mem-path=/dev/shm/ram0,share=on\ >>>      -machine memory-backend=ram0 \ >>>      -machine aux-ram-share=on \ >>>      -drive file=$ROOTFS,media=disk,if=virtio \ >>>      -qmp unix:$QMPSOCK,server=on,wait=off \ >>>      -nographic \ >>>      -device qxl-vga >> >> Run migration target: >>> EMULATOR=/path/to/emulator >>> ROOTFS=/path/to/image >>> QMPSOCK=/var/run/alma8qmp-dst.sock >>> $EMULATOR -enable-kvm \ >>>      -machine q35 \ >>>      -cpu host -smp 2 -m 2G \ >>>      -object memory-backend-file,id=ram0,size=2G,mem-path=/dev/shm/ram0,share=on\ >>>      -machine memory-backend=ram0 \ >>>      -machine aux-ram-share=on \ >>>      -drive file=$ROOTFS,media=disk,if=virtio \ >>>      -qmp unix:$QMPSOCK,server=on,wait=off \ >>>      -nographic \ >>>      -device qxl-vga \ >>>      -incoming tcp:0:44444 \ >>>      -incoming '{"channel-type": "cpr", "addr": { "transport": "socket", "type": "unix", "path": "/var/run/alma8cpr-dst.sock"}}' >> >> >> Launch the migration: >>> QMPSHELL=/root/src/qemu/master/scripts/qmp/qmp-shell >>> QMPSOCK=/var/run/alma8qmp-src.sock >>> >>> $QMPSHELL -p $QMPSOCK <>>      migrate-set-parameters mode=cpr-transfer >>>      migrate channels=[{"channel-type":"main","addr":{"transport":"socket","type":"inet","host":"0","port":"44444"}},{"channel-type":"cpr","addr":{"transport":"socket","type":"unix","path":"/var/run/alma8cpr-dst.sock"}}] >>> EOF >> >> Then, after a while, QXL guest driver on target crashes spewing the >> following messages: >>> [   73.962002] [TTM] Buffer eviction failed >>> [   73.962072] qxl 0000:00:02.0: object_init failed for (3149824, 0x00000001) >>> [   73.962081] [drm:qxl_alloc_bo_reserved [qxl]] *ERROR* failed to allocate VRAM BO >> >> That seems to be a known kernel QXL driver bug: >> >> https://lore.kernel.org/all/20220907094423.93581-1-min_halo@163.com/T/ >> https://lore.kernel.org/lkml/ZTgydqRlK6WX_b29@eldamar.lan/ >> >> (the latter discussion contains that reproduce script which speeds up >> the crash in the guest): >>> #!/bin/bash >>> >>> chvt 3 >>> >>> for j in $(seq 80); do >>>          echo "$(date) starting round $j" >>>          if [ "$(journalctl --boot | grep "failed to allocate VRAM BO")" != "" ]; then >>>                  echo "bug was reproduced after $j tries" >>>                  exit 1 >>>          fi >>>          for i in $(seq 100); do >>>                  dmesg > /dev/tty3 >>>          done >>> done >>> >>> echo "bug could not be reproduced" >>> exit 0 >> >> The bug itself seems to remain unfixed, as I was able to reproduce that >> with Fedora 41 guest, as well as AlmaLinux 8 guest. However our >> cpr-transfer code also seems to be buggy as it triggers the crash - >> without the cpr-transfer migration the above reproduce doesn't lead to >> crash on the source VM. >> >> I suspect that, as cpr-transfer doesn't migrate the guest memory, but >> rather passes it through the memory backend object, our code might >> somehow corrupt the VRAM.  However, I wasn't able to trace the >> corruption so far. >> >> Could somebody help the investigation and take a look into this?  Any >> suggestions would be appreciated.  Thanks! > > Possibly some memory region created by qxl is not being preserved. > Try adding these traces to see what is preserved: > > -trace enable='*cpr*' > -trace enable='*ram_alloc*' Also try adding this patch to see if it flags any ram blocks as not compatible with cpr. A message is printed at migration start time. https://lore.kernel.org/qemu-devel/1740667681-257312-1-git-send-email-steven.sistare@oracle.com/ - Steve