Re: [PATCH 2/2] iommu/vt-d: don's issue devTLB flush request when device is disconnected

Robin Murphy
2023-12-21T11:02:07Z

On 2023-12-21 10:42 am, Lukas Wunner wrote:
> On Wed, Dec 13, 2023 at 11:54:05AM +0000, Robin Murphy wrote:
>> I think if we want to ensure ATCs are invalidated on hot-unplug we need an
>> additional pre-removal notifier to take care of that, and that step would
>> then want to distinguish between an orderly removal where cleaning up is
>> somewhat meaningful, and a surprise removal where it definitely isn't.
>
> Even if a user starts the process for orderly removal, the device may be
> surprise-removed *during* that process. So we cannot assume that the
> device is actually accessible if orderly removal has been initiated.
> If the form factor supports surprise removal, the device may be gone
> at any time.

Sure, whatever we do there's always going to be some unavoidable
time-of-check-to-time-of-use race window so we can never guarantee that
sending a request to the device will succeed. I was just making the
point that if we *have* already detected a surprise removal, then
cleaning up its leftover driver model state should still generate a
BUS_NOTIFY_REMOVE_DEVICE call, but in that case we can know there's no
point trying to send any requests to the device that's already gone.

Thanks,
Robin.