mirror of https://github.com/xemu-project/xemu.git
3283843a8e
In qvring_init() we're writing vq->used->avail_event at "vq->used + 2 +
array_size". The struct pointed by vq->used is, from virtio_ring.h
Linux header):
* // A ring of used descriptor heads with free-running index.
* __virtio16 used_flags;
* __virtio16 used_idx;
* struct vring_used_elem used[num];
* __virtio16 avail_event_idx;
So 'flags' is the word right at vq->used. 'idx' is vq->used + 2. We need
to skip 'used_idx' by adding + 2 bytes, and then sum the vector size, to
reach avail_event_idx. An example on how to properly access this field
can be found in qvirtqueue_kick():
avail_event = qvirtio_readw(d, qts, vq->used + 4 +
sizeof(struct vring_used_elem) * vq->size);
This error was detected when enabling the RISC-V 'virt' libqos machine.
The 'idx' test from vhost-user-blk-test.c errors out with a timeout in
qvirtio_wait_used_elem(). The timeout happens because when processing
the first element, 'avail_event' is read in qvirtqueue_kick() as non-zero
because we didn't initialize it properly (and the memory at that point
happened to be non-zero). 'idx' is 0.
All of this makes this condition fail because "idx - avail_event" will
overflow and be non-zero:
/* < 1 because we add elements to avail queue one by one */
if ((flags & VRING_USED_F_NO_NOTIFY) == 0 &&
(!vq->event || (uint16_t)(idx-avail_event) < 1)) {
d->bus->virtqueue_kick(d, vq);
}
As a result the virtqueue is never kicked and we'll timeout waiting for it.
Fixes:
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| .. | ||
| avocado | ||
| bench | ||
| data | ||
| decode | ||
| docker | ||
| fp | ||
| guest-debug | ||
| image-fuzzer | ||
| include | ||
| keys | ||
| lcitool | ||
| migration | ||
| multiboot | ||
| perf/block/qcow2 | ||
| plugin | ||
| qapi-schema | ||
| qemu-iotests | ||
| qtest | ||
| rocker | ||
| tcg | ||
| tsan | ||
| uefi-test-tools | ||
| unit | ||
| vm | ||
| vmstate-static-checker-data | ||
| Makefile.include | ||
| dbus-vmstate-daemon.sh | ||
| meson.build | ||
| test-qht-par.c | ||
| vhost-user-bridge.c | ||