Re: [PATCH] virtio_pci: use irq to detect interrupt support

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Oct 14, 2022 at 12:09:20AM +0000, Angus Chen wrote:
> Hi Mst
> 
> > -----Original Message-----
> > From: Michael S. Tsirkin <mst@redhat.com>
> > Sent: Thursday, October 13, 2022 6:04 AM
> > To: linux-kernel@vger.kernel.org
> > Cc: Linus Torvalds <torvalds@linux-foundation.org>; Michael Ellerman
> > <mpe@ellerman.id.au>; Angus Chen <angus.chen@jaguarmicro.com>; Jason
> > Wang <jasowang@redhat.com>; virtualization@lists.linux-foundation.org
> > Subject: [PATCH] virtio_pci: use irq to detect interrupt support
> > 
> > commit 71491c54eafa ("virtio_pci: don't try to use intxif pin is zero")
> > breaks virtio_pci on powerpc, when running as a qemu guest.
> > 
> > vp_find_vqs() bails out because pci_dev->pin == 0.
> > 
> > But pci_dev->irq is populated correctly, so vp_find_vqs_intx() would
> > succeed if we called it - which is what the code used to do.
> > 
> > This seems to happen because pci_dev->pin is not populated in
> > pci_assign_irq().
> > 
> > Which is absolutely a bug in the relevant PCI code, but it
> > may also affect other platforms that use of_irq_parse_and_map_pci().
> > 
> > However Linus said:
> > 	The correct way to check for "no irq" doesn't use NO_IRQ at all, it just does
> > 		if (dev->irq) ...
> > so let's just check irq and be done with it.
> > 
> > Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> > Reported-by: Michael Ellerman <mpe@ellerman.id.au>
> > Fixes: 71491c54eafa ("virtio_pci: don't try to use intxif pin is zero")
> > Cc: "Angus Chen" <angus.chen@jaguarmicro.com>
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> > 
> > Build tested only - very late here. Angus any chance you could
> > help test this? Thanks!
> I tested the patch ，it work well on x86。Inlcude legacy and modern driver.
> And I tested it on arm server also，and find some problem because of 0.9.5 limitation.
>  "platform bug: legacy virtio-pci must not be used with RAM above 0x%llxGB\n",
>  But the error is not effected by our patch.with or without our patch ,it print the same.

Yes that's a limitation of 0.9.5 - just make a smaller VM to test
legacy.

> And I test modern dirver,it work well also.
> Sorry for the late reply.


Great, thanks a lot!

> > 
> >  drivers/virtio/virtio_pci_common.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/virtio/virtio_pci_common.c
> > b/drivers/virtio/virtio_pci_common.c
> > index 4df77eeb4d16..a6c86f916dbd 100644
> > --- a/drivers/virtio/virtio_pci_common.c
> > +++ b/drivers/virtio/virtio_pci_common.c
> > @@ -409,8 +409,8 @@ int vp_find_vqs(struct virtio_device *vdev, unsigned int
> > nvqs,
> >  	err = vp_find_vqs_msix(vdev, nvqs, vqs, callbacks, names, false, ctx, desc);
> >  	if (!err)
> >  		return 0;
> > -	/* Is there an interrupt pin? If not give up. */
> > -	if (!(to_vp_device(vdev)->pci_dev->pin))
> > +	/* Is there an interrupt? If not give up. */
> > +	if (!(to_vp_device(vdev)->pci_dev->irq))
> >  		return err;
> >  	/* Finally fall back to regular interrupts. */
> >  	return vp_find_vqs_intx(vdev, nvqs, vqs, callbacks, names, ctx);
> > --
> > MST
> 

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