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

[Philippe Mathieu-Daudé]

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 Otherwise the region might have outdated memory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.