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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 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*' - Steve