crosvm virtio-gpu can't create virt-queue

[lttle sad]

Hello,

I want to check myos's virtio-gpu device, so, I use command run myos:

cargo run --features=gpu,x,virgl_renderer,virgl_renderer_next -- run \
    --cpus 8 \
    --mem 1024 \
    --disable-sandbox \
    --gpu backend=virglrenderer,width=1920,height=1080 \
    ./myos

During myos initialization，like Linux，cerate two queue for virtio_gpu.

First queue:ctrlq，create success,

But, second queue:cursorq, create failed. And, crosvm report a WRONG:

[2022-12-05T19:40:19.384103334+08:00 WARN  devices::virtio::queue] ignoring write to vector on ready queue

And, when I try to get EDID from host virtio-gpu, I sent meg, but I received zero intrrrput.

Under normal conditions, in linux code, two queue could create success and could get interrupt. But I am in an abnormal conditions.

It seems like my crosvm commands Error ?

Why crosvm tells me WRONG ?

Why I can't communicate with host virtio-gpu ? 

I am so confused,

Hope your help,

thanks

[Daniel Verkamp]

Hi,

According to the virtio specification (Virtio 1.2, section 4.1.4.3.2,
"Driver Requirements: Common configuration structure layout"), the
per-queue configuration (including the MSI-X vector) needs to happen
before enabling the queue ("enabled" is referred to as "ready" in the
crosvm code):
> The driver MUST configure the other virtqueue fields before enabling the virtqueue with queue_enable.

It seems that the driver is attempting to change the MSI-X vector for
a queue after that queue was enabled. It should be possible to avoid
the problem by configuring queue_msix_vector before enabling the
queue.

Side note: maybe my reading of the virtio spec is not totally accurate
(the quoted line above doesn't explicitly prohibit the driver from
writing to the virtqueue-specific fields after enabling the queue,
just requires that they are initialized before enabling), but that is
the current behavior of crosvm virtio devices.

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