On Mon, Oct 19, 2020 at 02:16:08PM -0700, Raj, Ashok wrote: > Hi Jean > > On Mon, Oct 19, 2020 at 04:08:24PM +0200, Jean-Philippe Brucker 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: > > The goal is we do this when the device is in a messup up state. So we can't > take for granted the device is properly operating which is why we are going > to wack the device with a flr(). > > The only thing that's supposed to work without a brain freeze is the > invalidation logic. Spec requires devices to respond to invalidations even when > they are in the process of flr(). > > So when IOMMU does an invalidation wait with a Page-Drain, IOMMU waits till > the response for that arrives before completing the descriptor. Due to > the posted semantics it will ensure any PR's issued and in the fabric are flushed > out to memory. > > I suppose you can wait for the device to vouch for all responses, but that > is assuming the device is still functioning properly. Given that we use it > in two places, > > * Reclaiming a PASID - only during a tear down sequence, skipping it > doesn't really buy us much. Yes I was only wondering about normal PASID reclaim operations, in unbind(). Agreed that for FLR we need to properly clean the queue, though I do need to do more thinking about this. Anyway, having a full priq drain in unbind() isn't harmful, just unnecessary delay in my opinion. I'll drop these patches for now but thanks for the discussion. Thanks, Jean > * During FLR this can't be skipped anyway due to the above sequence > requirement. > > > > > "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. > > > > Cheers, > Ashok
