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

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On Fri, Sep 22, 2023 at 8:25 PM Parav Pandit <parav@xxxxxxxxxx> wrote:
> > From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> > Sent: Friday, September 22, 2023 5:53 PM
> > > And what's more, using MMIO BAR0 then it can work for legacy.
> >
> > Oh? How? Our team didn't think so.
> It does not. It was already discussed.
> The device reset in legacy is not synchronous.

How do you know this?

> The drivers do not wait for reset to complete; it was written for the sw backend.

Do you see there's a flush after reset in the legacy driver?

static void vp_reset(struct virtio_device *vdev)
        struct virtio_pci_device *vp_dev = to_vp_device(vdev);
        /* 0 status means a reset. */
        vp_legacy_set_status(&vp_dev->ldev, 0);
        /* Flush out the status write, and flush in device writes,
         * including MSi-X interrupts, if any. */
        /* Flush pending VQ/configuration callbacks. */


> Hence MMIO BAR0 is not the best option in real implementations.

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