Re: [PATCH vfio 11/11] vfio/virtio: Introduce a vfio driver over virtio devices

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On Tue, Sep 26, 2023 at 7:49 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
>
> On Tue, Sep 26, 2023 at 10:32:39AM +0800, Jason Wang wrote:
> > It's the implementation details in legacy. The device needs to make
> > sure (reset) the driver can work (is done before get_status return).
>
> I think that there's no way to make it reliably work for all legacy drivers.

Yes, we may have ancient drivers.

>
> They just assumed a software backend and did not bother with DMA
> ordering. You can try to avoid resets, they are not that common so
> things will tend to mostly work if you don't stress them to much with
> things like hot plug/unplug in a loop.  Or you can try to use a driver
> after 2011 which is more aware of hardware ordering and flushes the
> reset write with a read.  One of these two tricks, I think, is the magic
> behind the device exposing memory bar 0 that you mention.

Right this is what I see for hardware legacy devices shipped by some
cloud vendors.

Thanks

>
> --
> MST
>





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