On Mon, Oct 19, 2020 at 11:33:16AM -0700, Jacob Pan wrote: > Hi Jean-Philippe, > > On Mon, 19 Oct 2020 16:08:24 +0200, Jean-Philippe Brucker > <jean-philippe@xxxxxxxxxx> wrote: > > > On Sat, Oct 17, 2020 at 04:25:25AM -0700, Raj, Ashok wrote: > > > > For devices that *don't* use a stop marker, the PCIe spec says > > > > (10.4.1.2): > > > > > > > > To stop [using a PASID] without using a Stop Marker Message, the > > > > function shall: > > > > 1. Stop queueing new Page Request Messages for this PASID. > > > > > > The device driver would need to tell stop sending any new PR's. > > > > > > > 2. Finish transmitting any multi-page Page Request Messages for this > > > > PASID (i.e. send the Page Request Message with the L bit Set). > > > > 3. Wait for PRG Response Messages associated any outstanding Page > > > > Request Messages for the PASID. > > > > > > > > So they have to flush their PR themselves. And since the device driver > > > > completes this sequence before calling unbind(), then there shouldn't > > > > be any oustanding PR for the PASID, and unbind() doesn't need to > > > > flush, right? > > > > > > I can see how the device can complete #2,3 above. But the device driver > > > isn't the one managing page-responses right. So in order for the device > > > to know the above sequence is complete, it would need to get some > > > assist from IOMMU driver? > > > > No the device driver just waits for the device to indicate that it has > > completed the sequence. That's what the magic stop-PASID mechanism > > described by PCIe does. In 6.20.1 "Managing PASID TLP Prefix Usage" it > > says: > > > > "A Function must have a mechanism to request that it gracefully stop using > > a specific PASID. This mechanism is device specific but must satisfy the > > following rules: > > [...] > > * When the stop request mechanism indicates completion, the Function has: > > [...] > > * Complied with additional rules described in Address Translation > > Services (Chapter 10 [10.4.1.2 quoted above]) if Address Translations > > or Page Requests were issued on the behalf of this PASID." > > > > So after the device driver initiates this mechanism in the device, the > > device must be able to indicate completion of the mechanism, which > > includes completing all in-flight Page Requests. At that point the device > > driver can call unbind() knowing there is no pending PR for this PASID. > > > In step #3, I think it is possible that device driver received page response > as part of the auto page response, so it may not guarantee all the in-flight > PRQs are completed inside IOMMU. Therefore, drain is _always_ needed to be > sure? So I don't think that's a problem, because non-last PR are not handled by IOPF until the last PR is received. And when the IOMMU driver detects that the queue has been overflowing and could have auto-responded to last PR, we discard any pending non-last PR. I couldn't find a leak here. Thanks, Jean
