On Fri, 03/13 14:07, Fam Zheng wrote:
> On Thu, 03/12 12:15, Michael S. Tsirkin wrote:
> > On Thu, Mar 12, 2015 at 11:04:33AM +0000, Peter Maydell wrote:
> > > On 12 March 2015 at 10:57, Michael S. Tsirkin <m...@redhat.com> wrote:
> > > > This isn't a device reset though.
> > > > The function that Fam is touching is called
> > > > when a special "virtio reset" register to
> > > > poked by the driver.
> > > > It only resets part of the device, not all of it,
> > > > and it seems reasonable to ask that it clear the
> > > > interrupt.
> > >
> > > Oh, right, sorry. Yes, that should clear the interrupt, then.
> > > (Is there a similar bug on other virtio transports?)
> > >
> > > -- PMM
> >
> > Hmm interesting.
> >
> > I looked at virtio_reset and that one does:
> > vdev->isr = 0;
> > vdev->config_vector = VIRTIO_NO_VECTOR;
> > virtio_notify_vector(vdev, vdev->config_vector);
> >
> > which in turn would call
> > static void virtio_pci_notify(DeviceState *d, uint16_t vector)
> > {
> > VirtIOPCIProxy *proxy = to_virtio_pci_proxy_fast(d);
> >
> > if (msix_enabled(&proxy->pci_dev))
> > msix_notify(&proxy->pci_dev, vector);
> > else {
> > VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
> > pci_set_irq(&proxy->pci_dev, vdev->isr & 1);
> > }
> > }
> >
> > since isr is 0, and msi is disabled, it looks like
> > pci_set_irq will get invoked automatically.
> >
> > so at this point I stopped understanding how can
> > this patch help.
> >
> > Fam, does your patch actually help some guests?
> > Could you pls investigate why isn't virtio_reset
> > sufficient?
>
> Because virtio_reset doesn't disable msix, so here
> "msix_notify(&proxy->pci_dev, 0)" is called.
s/0/VIRTIO_NO_VECTOR/
>
> I tested by applying your patch:
>
> http://www.spinics.net/lists/kernel/msg1943182.html
>
> and adding printf's in QEMU's virtio_reset and virtio_pci_notify.
>
> It shows pci_set_irq is never called.
>
> Fam
>
>
