Re: [PATCH] hw/virtio: Update vring after modifying its queue size

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Thu, Aug 26, 2021 at 12:42:56AM +0200, Philippe Mathieu-Daudé wrote:
> When a ring queue size is modified, we need to call
> virtio_queue_update_rings() to re-init the memory region
> caches. Otherwise the region might have outdated memory
> size, and later load/store access might trigger an
> assertion, such:
> 
>   qemu-system-i386: include/exec/memory_ldst_cached.h.inc:30: uint16_t address_space_lduw_le_cached(MemoryRegionCache *, hwaddr, MemTxAttrs, MemTxResult *):
>   Assertion `addr < cache->len && 2 <= cache->len - addr' failed.
>   Thread 1 "qemu-system-i38" received signal SIGABRT, Aborted.
>   0x00007ffff4d312a2 in raise () from /lib64/libc.so.6
>   (gdb) bt
>   #1  0x00007ffff4d1a8a4 in abort () at /lib64/libc.so.6
>   #4  0x0000555558f2b8ec in address_space_lduw_le_cached (cache=0x61300010a7c0, addr=134, attrs=..., result=0x0) at include/exec/memory_ldst_cached.h.inc:30
>   #5  0x0000555558f2ac6b in lduw_le_phys_cached (cache=0x61300010a7c0, addr=134) at include/exec/memory_ldst_phys.h.inc:67
>   #6  0x0000555558f2a3cd in virtio_lduw_phys_cached (vdev=0x62d00003a680, cache=0x61300010a7c0, pa=134) at include/hw/virtio/virtio-access.h:166
>   #7  0x0000555558f300ea in vring_avail_ring (vq=0x7fffdd55d8a0, i=65) at hw/virtio/virtio.c:326
>   #8  0x0000555558f33b10 in vring_get_used_event (vq=0x7fffdd55d8a0) at hw/virtio/virtio.c:332
>   #9  0x0000555558f33677 in virtio_split_should_notify (vdev=0x62d00003a680, vq=0x7fffdd55d8a0) at hw/virtio/virtio.c:2471
>   #10 0x0000555558f1859f in virtio_should_notify (vdev=0x62d00003a680, vq=0x7fffdd55d8a0) at hw/virtio/virtio.c:2523
>   #11 0x0000555558f188cc in virtio_notify (vdev=0x62d00003a680, vq=0x7fffdd55d8a0) at hw/virtio/virtio.c:2565
>   #12 0x0000555557c2bd52 in virtio_input_handle_sts (vdev=0x62d00003a680, vq=0x7fffdd55d8a0) at hw/input/virtio-input.c:100
>   #13 0x0000555558f16df7 in virtio_queue_notify (vdev=0x62d00003a680, n=1) at hw/virtio/virtio.c:2363
>   #14 0x00005555583f45c0 in virtio_pci_notify_write (opaque=0x62d000032400, addr=7, val=0, size=1) at hw/virtio/virtio-pci.c:1369
>   #15 0x0000555558b80b04 in memory_region_write_accessor (mr=0x62d000033190, addr=7, value=0x7fffffff8eb0, size=1, shift=0, mask=255, attrs=...) at softmmu/memory.c:492
> 
> Reported-by: Qiuhao Li <Qiuhao.Li@outlook.com>
> Fixes: ab223c9518e ("virtio: allow virtio-1 queue layout")
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/302
> BugLink: https://bugs.launchpad.net/qemu/+bug/1913510
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
>  hw/virtio/virtio.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 874377f37a7..04ffe5f420e 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -2255,6 +2255,7 @@ void virtio_queue_set_num(VirtIODevice *vdev, int n, int num)
>          return;
>      }
>      vdev->vq[n].vring.num = num;
> +    virtio_queue_update_rings(vdev, n);
>  }

Can this line in hw/virtio/virtio-mmio.c be removed now?

    case VIRTIO_MMIO_QUEUE_NUM:
        trace_virtio_mmio_queue_write(value, VIRTQUEUE_MAX_SIZE);
        virtio_queue_set_num(vdev, vdev->queue_sel, value);

        if (proxy->legacy) {
            virtio_queue_update_rings(vdev, vdev->queue_sel);
	    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Stefan

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