From 5bcbdfefff3209a194168dbe772c7e2f45d248f7 Mon Sep 17 00:00:00 2001

From: Maxim Levitsky <mlevitsk@redhat.com>

Date: Sun, 22 Dec 2019 11:02:07 +0100

Subject: [PATCH 2/7] virtio: Return true from virtio_queue_empty if broken

RH-Author: Maxim Levitsky <mlevitsk@redhat.com>

Message-id: <20191222110207.21384-3-mlevitsk@redhat.com>

Patchwork-id: 93208

O-Subject: [RHEL-8.2.0 qemu-kvm PATCH 2/2] virtio: Return true from virtio_queue_empty if broken

Bugzilla: 1769613

RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>

RH-Acked-by: Cornelia Huck <cohuck@redhat.com>

RH-Acked-by: Peter Xu <peterx@redhat.com>

From: Fam Zheng <famz@redhat.com>

Both virtio-blk and virtio-scsi use virtio_queue_empty() as the

loop condition in VQ handlers (virtio_blk_handle_vq,

virtio_scsi_handle_cmd_vq). When a device is marked broken in

virtqueue_pop, for example if a vIOMMU address translation failed, we

want to break out of the loop.

This fixes a hanging problem when booting a CentOS 3.10.0-862.el7.x86_64

kernel with ATS enabled:

  $ qemu-system-x86_64 \

    ... \

    -device intel-iommu,intremap=on,caching-mode=on,eim=on,device-iotlb=on \

    -device virtio-scsi-pci,iommu_platform=on,ats=on,id=scsi0,bus=pci.4,addr=0x0

The dead loop happens immediately when the kernel boots and initializes

the device, where virtio_scsi_data_plane_handle_cmd will not return:

    > ...

    > #13 0x00005586602b7793 in virtio_scsi_handle_cmd_vq

    > #14 0x00005586602b8d66 in virtio_scsi_data_plane_handle_cmd

    > #15 0x00005586602ddab7 in virtio_queue_notify_aio_vq

    > #16 0x00005586602dfc9f in virtio_queue_host_notifier_aio_poll

    > #17 0x00005586607885da in run_poll_handlers_once

    > #18 0x000055866078880e in try_poll_mode

    > #19 0x00005586607888eb in aio_poll

    > #20 0x0000558660784561 in aio_wait_bh_oneshot

    > #21 0x00005586602b9582 in virtio_scsi_dataplane_stop

    > #22 0x00005586605a7110 in virtio_bus_stop_ioeventfd

    > #23 0x00005586605a9426 in virtio_pci_stop_ioeventfd

    > #24 0x00005586605ab808 in virtio_pci_common_write

    > #25 0x0000558660242396 in memory_region_write_accessor

    > #26 0x00005586602425ab in access_with_adjusted_size

    > #27 0x0000558660245281 in memory_region_dispatch_write

    > #28 0x00005586601e008e in flatview_write_continue

    > #29 0x00005586601e01d8 in flatview_write

    > #30 0x00005586601e04de in address_space_write

    > #31 0x00005586601e052f in address_space_rw

    > #32 0x00005586602607f2 in kvm_cpu_exec

    > #33 0x0000558660227148 in qemu_kvm_cpu_thread_fn

    > #34 0x000055866078bde7 in qemu_thread_start

    > #35 0x00007f5784906594 in start_thread

    > #36 0x00007f5784639e6f in clone

With this patch, virtio_queue_empty will now return 1 as soon as the

vdev is marked as broken, after a "virtio: zero sized buffers are not

allowed" error.

To be consistent, update virtio_queue_empty_rcu as well.

Signed-off-by: Fam Zheng <famz@redhat.com>

Message-Id: <20180910145616.8598-2-famz@redhat.com>

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

(cherry picked from commit 2d1df8591022737b8ef19d681ff74eda389f5198)

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>

---

 hw/virtio/virtio.c | 8 ++++++++

 1 file changed, 8 insertions(+)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c

index 1debb01..fce199e 100644

--- a/hw/virtio/virtio.c

+++ b/hw/virtio/virtio.c

@@ -344,6 +344,10 @@ int virtio_queue_ready(VirtQueue *vq)

  * Called within rcu_read_lock().  */

 static int virtio_queue_empty_rcu(VirtQueue *vq)

 {

+    if (unlikely(vq->vdev->broken)) {

+        return 1;

+    }

+

     if (unlikely(!vq->vring.avail)) {

         return 1;

     }

@@ -359,6 +363,10 @@ int virtio_queue_empty(VirtQueue *vq)

 {

     bool empty;

+    if (unlikely(vq->vdev->broken)) {

+        return 1;

+    }

+

     if (unlikely(!vq->vring.avail)) {

         return 1;

     }

-- 

1.8.3.1