Re: [PATCH v2] pci/ats: do not allow broken devices to be assigned to guests

[Jan Beulich <jbeulich@xxxxxxxx>]

On 25.02.2022 09:41, Roger Pau Monné wrote:
> On Thu, Feb 24, 2022 at 05:43:13PM +0100, Jan Beulich wrote:
>> On 24.02.2022 17:37, Roger Pau Monne wrote:
>>> Introduce a new field to mark devices as broken: having it set
>>> prevents the device from being assigned to guests. Use the field in
>>> order to mark ATS devices that have failed a flush as broken, thus
>>> preventing them to be assigned to any guest.
>>>
>>> This allows the device IOMMU context entry to be cleaned up properly,
>>> as calling _pci_hide_device will just change the ownership of the
>>> device, but the IOMMU context entry of the device would be left as-is.
>>> It would also leak a Domain ID, as removing the device from it's
>>> previous owner will allow releasing the DID used by the device without
>>> having cleaned up the context entry.
>>
>> This DID aspect is VT-d specific, isn't it? I'd be inclined to ask to
>> make this explicit (which could be done while committing if no other
>> need for a v3 arises).
> 
> Indeed. AMD doesn't use iommu_dev_iotlb_flush_timeout so the function
> is VT-d specific.

But perhaps wrongly so. Which is why I'd prefer to ...

> What about using:
> 
> "Introduce a new field to mark devices as broken: having it set
> prevents the device from being assigned to guests. Use the field in
> order to mark ATS devices that have failed a flush when using VT-d as
> broken, thus preventing them to be assigned to any guest.

... omit VT-d here (i.e. leave this paragraph as you had it before),
but ...

> This allows the device IOMMU context entry to be cleaned up properly,
> as calling _pci_hide_device will just change the ownership of the
> device, but the IOMMU context entry of the device would be left as-is.
> It would also leak a VT-d Domain ID if using one, as removing the
> device from it's previous owner will allow releasing the IOMMU DID
> used by the device without having cleaned up the context entry."

... use this as replacement.

Jan