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

[Michael S. Tsirkin]

On Thu, Aug 26, 2021 at 10:40:47AM +0200, Philippe Mathieu-Daudé wrote:
> On 8/26/21 5:28 AM, Jason Wang wrote:
> > On Thu, Aug 26, 2021 at 6:43 AM Philippe Mathieu-Daudé
> > <philmd@redhat.com> 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 Otherwise the region might have outdated memory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);
> >>  }
> >>
> > 
> > Spec said:
> > 
> > "
> > The driver MUST configure the other virtqueue fields before enabling
> > the virtqueue with queue_enable.
> > "
> > 
> > So I think we should forbid the num to be changed if the virtqueue is ready?
> 
> Alright. virtio_pci_common_write() doesn't report errors although.

It can't - just log guest error and ignore. Maybe set needs_reset ...

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MST