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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Jason Wang <jasowang@redhat.com>,
        "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [PATCH 6/9] virtio_pci: harden MSI-X interrupts
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Date:   Mon, 13 Sep 2021 21:38:30 +0200
Message-ID: <87bl4wfeq1.ffs@tglx>
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On Mon, Sep 13 2021 at 15:07, Jason Wang wrote:
> On Mon, Sep 13, 2021 at 2:50 PM Michael S. Tsirkin <mst@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