Re: [PATCH v4 4/7] vfio: ap: register IOMMU VFIO notifier

Christian Borntraeger
2019-03-01T07:51:52Z

On 28.02.2019 17:55, Halil Pasic wrote:
> On Thu, 28 Feb 2019 09:48:39 +0100
> Pierre Morel <pmorel@linux.ibm.com> wrote:
>
>> On 28/02/2019 09:23, Christian Borntraeger wrote:
>>> On 22.02.2019 16:29, Pierre Morel wrote:
>>>> To be able to use the VFIO interface to facilitate the
>>>> mediated device memory pining/unpining we need to register
>>>> a notifier for IOMMU.
>>>
>>> You might want to add that while we start to pin one guest page for the
>>> interrupt indicator byte in the next patch, this is still ok with ballooning
>>> as this page will never be used by the guest virtio-balloon driver. So the
>>> pinned page will never be freed. And even a broken guest does so, that would
>>> not impact the host as the original page is still in control by vfio.
>>>
>>
>> Thanks, I ll do.
>>
>
> I recall a comment in qemu that says vfio-ap does not pin any pages.
> That one needs to be fixed up as well.

Yes, something along the line that we do pin the interrupt indicator pages
but those do not change regularly and we stay in lockstep with the guest.
At the same time the guest driver will keep that page allocate so virtio-balloon
will not take them.