Linux Virtualization - Sep 2021 - [PATCH 6/9] virtio_pci: harden MSI-X interrupts

On Mon, Sep 13 2021 at 15:07, Jason Wang wrote:
> On Mon, Sep 13, 2021 at 2:50 PM Michael S. Tsirkin <mst at
redhat.com> wrote:
>> > But doen't "irq is disabled" basically mean "we
told the hypervisor
>> > to disable the irq"?  What extractly prevents hypervisor from
>> > sending the irq even if guest thinks it disabled it?
>>
>> More generally, can't we for example blow away the
>> indir_desc array that we use to keep the ctx pointers?
>> Won't that be enough?
>
> I'm not sure how it is related to the indirect descriptor but an
> example is that all the current driver will assume:
>
> 1) the interrupt won't be raised before virtio_device_ready()
> 2) the interrupt won't be raised after reset()
If that assumption exists, then you better keep the interrupt line
disabled until virtio_device_ready() has completed and disable it again
before reset() is invoked. That's a question of general robustness and
not really a question of trusted hypervisors and encrypted guests.
>> > > > > > > +void vp_disable_vectors(struct
virtio_device *vdev)
>> > > > > > >  {
>> > > > > > >       struct virtio_pci_device *vp_dev =
to_vp_device(vdev);
>> > > > > > >       int i;
>> > > > > > > @@ -34,7 +34,20 @@ void
vp_synchronize_vectors(struct virtio_device *vdev)
>> > > > > > >              
synchronize_irq(vp_dev->pci_dev->irq);
Don't you want the same change for non-MSI interrupts?

Thanks,

        tglx

On Mon, Sep 13, 2021 at 09:38:30PM +0200, Thomas Gleixner
wrote:
> On Mon, Sep 13 2021 at 15:07, Jason Wang wrote:
> > On Mon, Sep 13, 2021 at 2:50 PM Michael S. Tsirkin <mst at
redhat.com> wrote:
> >> > But doen't "irq is disabled" basically mean
"we told the hypervisor
> >> > to disable the irq"?  What extractly prevents hypervisor
from
> >> > sending the irq even if guest thinks it disabled it?
> >>
> >> More generally, can't we for example blow away the
> >> indir_desc array that we use to keep the ctx pointers?
> >> Won't that be enough?
> >
> > I'm not sure how it is related to the indirect descriptor but an
> > example is that all the current driver will assume:
> >
> > 1) the interrupt won't be raised before virtio_device_ready()
> > 2) the interrupt won't be raised after reset()
> 
> If that assumption exists, then you better keep the interrupt line
> disabled until virtio_device_ready() has completed
started not completed. device is allowed to send
config interrupts right after DRIVER_OK status is set by
virtio_device_ready.
> and disable it again
> before reset() is invoked. That's a question of general robustness and
> not really a question of trusted hypervisors and encrypted guests.
We can do this for some MSIX interrupts, sure. Not for shared interrupts though.
> >> > > > > > > +void vp_disable_vectors(struct
virtio_device *vdev)
> >> > > > > > >  {
> >> > > > > > >       struct virtio_pci_device
*vp_dev = to_vp_device(vdev);
> >> > > > > > >       int i;
> >> > > > > > > @@ -34,7 +34,20 @@ void
vp_synchronize_vectors(struct virtio_device *vdev)
> >> > > > > > >              
synchronize_irq(vp_dev->pci_dev->irq);
> 
> Don't you want the same change for non-MSI interrupts?

We can't disable them - these are shared.
> Thanks,
> 
>         tglx