bwlp/qemu.git/hw/block/dataplane, branch spice_video_codecs

virtio-scsi: fix race in virtio_scsi_dataplane_start()

2022-08-17T11:07:37+00:00

As soon as virtio_scsi_data_plane_start() attaches host notifiers the IOThread may start virtqueue processing. There is a race between IOThread virtqueue processing and virtio_scsi_data_plane_start() because it only assigns s->dataplane_started after attaching host notifiers. When a virtqueue handler function in the IOThread calls virtio_scsi_defer_to_dataplane() it may see !s->dataplane_started and attempt to start dataplane even though we're already in the IOThread: #0 0x00007f67b360857c __pthread_kill_implementation (libc.so.6 + 0xa257c) #1 0x00007f67b35bbd56 raise (libc.so.6 + 0x55d56) #2 0x00007f67b358e833 abort (libc.so.6 + 0x28833) #3 0x00007f67b358e75b __assert_fail_base.cold (libc.so.6 + 0x2875b) #4 0x00007f67b35b4cd6 __assert_fail (libc.so.6 + 0x4ecd6) #5 0x000055ca87fd411b memory_region_transaction_commit (qemu-kvm + 0x67511b) #6 0x000055ca87e17811 virtio_pci_ioeventfd_assign (qemu-kvm + 0x4b8811) #7 0x000055ca87e14836 virtio_bus_set_host_notifier (qemu-kvm + 0x4b5836) #8 0x000055ca87f8e14e virtio_scsi_set_host_notifier (qemu-kvm + 0x62f14e) #9 0x000055ca87f8dd62 virtio_scsi_dataplane_start (qemu-kvm + 0x62ed62) #10 0x000055ca87e14610 virtio_bus_start_ioeventfd (qemu-kvm + 0x4b5610) #11 0x000055ca87f8c29a virtio_scsi_handle_ctrl (qemu-kvm + 0x62d29a) #12 0x000055ca87fa5902 virtio_queue_host_notifier_read (qemu-kvm + 0x646902) #13 0x000055ca882c099e aio_dispatch_handler (qemu-kvm + 0x96199e) #14 0x000055ca882c1761 aio_poll (qemu-kvm + 0x962761) #15 0x000055ca880e1052 iothread_run (qemu-kvm + 0x782052) #16 0x000055ca882c562a qemu_thread_start (qemu-kvm + 0x96662a) This patch assigns s->dataplane_started before attaching host notifiers so that virtqueue handler functions that run in the IOThread before virtio_scsi_data_plane_start() returns correctly identify that dataplane does not need to be started. This fix is taken from the virtio-blk dataplane code and it's worth adding a comment in virtio-blk as well to explain why it works. Note that s->dataplane_started does not need the AioContext lock because it is set before attaching host notifiers and cleared after detaching host notifiers. In other words, the IOThread always sees the value true and the main loop thread does not modify it while the IOThread is active. Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2099541 Reported-by: Qing Wang Signed-off-by: Stefan Hajnoczi Message-Id: <20220808162134.240405-1-stefanha@redhat.com> Reviewed-by: Emanuele Giuseppe Esposito Reviewed-by: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin

osdep: Move memalign-related functions to their own header

2022-03-07T13:16:49+00:00

Move the various memalign-related functions out of osdep.h and into their own header, which we include only where they are used. While we're doing this, add some brief documentation comments. Signed-off-by: Peter Maydell Reviewed-by: Richard Henderson Reviewed-by: Philippe Mathieu-Daudé Message-id: 20220226180723.1706285-10-peter.maydell@linaro.org

virtio: unify dataplane and non-dataplane ->handle_output()

2022-01-12T17:09:39+00:00

Now that virtio-blk and virtio-scsi are ready, get rid of the handle_aio_output() callback. It's no longer needed. Signed-off-by: Stefan Hajnoczi Reviewed-by: Stefano Garzarella Message-id: 20211207132336.36627-7-stefanha@redhat.com Signed-off-by: Stefan Hajnoczi

virtio: get rid of VirtIOHandleAIOOutput

2022-01-12T17:09:39+00:00

The virtqueue host notifier API virtio_queue_aio_set_host_notifier_handler() polls the virtqueue for new buffers. AioContext previously required a bool progress return value indicating whether an event was handled or not. This is no longer necessary because the AioContext polling API has been split into a poll check function and an event handler function. The event handler is only run when we know there is work to do, so it doesn't return bool. The VirtIOHandleAIOOutput function signature is now the same as VirtIOHandleOutput. Get rid of the bool return value. Further simplifications will be made for virtio-blk and virtio-scsi in the next patch. Signed-off-by: Stefan Hajnoczi Reviewed-by: Stefano Garzarella Message-id: 20211207132336.36627-3-stefanha@redhat.com Signed-off-by: Stefan Hajnoczi

virtio-blk: Fix clean up of host notifiers for single MR transaction.

2021-12-06T14:21:14+00:00

The code that introduced "virtio-blk: Configure all host notifiers in a single MR transaction" introduced a second loop variable to perform cleanup in second loop, but mistakenly still refers to the first loop variable within the second loop body. Fixes: d0267da61489 ("virtio-blk: Configure all host notifiers in a single MR transaction") Signed-off-by: Mark Mielke Message-id: CALm7yL08qarOu0dnQkTN+pa=BSRC92g31YpQQNDeAiT4yLZWQQ@mail.gmail.com Signed-off-by: Stefan Hajnoczi

virtio: Clarify MR transaction optimization

2021-07-02T15:13:39+00:00

The device model batching its ioeventfds in a single MR transaction is an optimization. Clarify this in virtio-scsi, virtio-blk and generic virtio code. Also clarify that the transaction must commit before closing ioeventfds so that no one is tempted to merge the loops in the start functions error path and in the stop functions. Signed-off-by: Greg Kurz Message-Id: <162125799728.1394228.339855768563326832.stgit@bahia.lan> Reviewed-by: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin Reviewed-by: Stefan Hajnoczi Reviewed-by: Stefan Hajnoczi Reviewed-by: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin

docs: fix references to docs/devel/tracing.rst

2021-06-02T04:51:09+00:00

Commit e50caf4a5c ("tracing: convert documentation to rST") converted docs/devel/tracing.txt to docs/devel/tracing.rst. We still have several references to the old file, so let's fix them with the following command: sed -i s/tracing.txt/tracing.rst/ $(git grep -l docs/devel/tracing.txt) Signed-off-by: Stefano Garzarella Reviewed-by: Philippe Mathieu-Daudé Message-Id: <20210517151702.109066-2-sgarzare@redhat.com> Signed-off-by: Thomas Huth

virtio-blk: Configure all host notifiers in a single MR transaction

2021-05-14T14:26:18+00:00

This allows the virtio-blk-pci device to batch the setup of all its host notifiers. This significantly improves boot time of VMs with a high number of vCPUs, e.g. from 3m26.186s down to 0m58.023s for a pseries machine with 384 vCPUs. Note that memory_region_transaction_commit() must be called before virtio_bus_cleanup_host_notifier() because the latter might close ioeventfds that the transaction still assumes to be around when it commits. Signed-off-by: Greg Kurz Message-Id: <20210407143501.244343-3-groug@kaod.org> Reviewed-by: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin

virtio-blk: Fix rollback path in virtio_blk_data_plane_start()

2021-05-14T14:26:18+00:00

When dataplane multiqueue support was added in QEMU 2.7, the path that would rollback guest notifiers assignment in case of error simply got dropped. Later on, when Error was added to blk_set_aio_context() in QEMU 4.1, another error path was introduced, but it ommits to rollback both host and guest notifiers. It seems cleaner to fix the rollback path in one go. The patch is simple enough that it can be adjusted if backported to a pre-4.1 QEMU. Fixes: 51b04ac5c6a6 ("virtio-blk: dataplane multiqueue support") Cc: stefanha@redhat.com Fixes: 97896a4887a0 ("block: Add Error to blk_set_aio_context()") Cc: kwolf@redhat.com Signed-off-by: Greg Kurz Reviewed-by: Stefan Hajnoczi Message-Id: <20210407143501.244343-2-groug@kaod.org> Reviewed-by: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin

block: Separate blk_is_writable() and blk_supports_write_perm()

2021-01-27T19:45:20+00:00

Currently, blk_is_read_only() tells whether a given BlockBackend can only be used in read-only mode because its root node is read-only. Some callers actually try to answer a slightly different question: Is the BlockBackend configured to be writable, by taking write permissions on the root node? This can differ, for example, for CD-ROM devices which don't take write permissions, but may be backed by a writable image file. scsi-cd allows write requests to the drive if blk_is_read_only() returns false. However, the write request will immediately run into an assertion failure because the write permission is missing. This patch introduces separate functions for both questions. blk_supports_write_perm() answers the question whether the block node/image file can support writable devices, whereas blk_is_writable() tells whether the BlockBackend is currently configured to be writable. All calls of blk_is_read_only() are converted to one of the two new functions. Fixes: https://bugs.launchpad.net/bugs/1906693 Cc: qemu-stable@nongnu.org Signed-off-by: Kevin Wolf Message-Id: <20210118123448.307825-2-kwolf@redhat.com> Reviewed-by: Philippe Mathieu-Daudé Reviewed-by: Max Reitz Signed-off-by: Kevin Wolf