Re: [RFC PATCH 0/2] iommu: Avoid unnecessary PRI queue flushes
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 ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [RFC PATCH 0/2] iommu: Avoid unnecessary PRI queue flushes
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 > 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 ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [RFC PATCH 0/2] iommu: Avoid unnecessary PRI queue flushes
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. * 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 ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [RFC PATCH 0/2] iommu: Avoid unnecessary PRI queue flushes
Hi Jean-Philippe, On Mon, 19 Oct 2020 16:08:24 +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: > > "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? > Thanks, > Jean > > > > > How does the driver know that everything host received has been > > responded back to device? > > > > > > > > > I'm not sure about other IOMMU's how they behave, When there is no > > > > space in the PRQ, IOMMU auto-responds to the device. This puts the > > > > device in a while (1) loop. The fake successful response will let > > > > the device do a ATS lookup, and that would fail forcing the device > > > > to do another PRQ. > > > > > > But in the sequence above, step 1 should ensure that the device will > > > not send another PR for any successful response coming back at step > > > 3. > > > > True, but there could be some page-request in flight on its way to the > > IOMMU. By draining and getting that round trip back to IOMMU we > > gaurantee things in flight are flushed to PRQ after that Drain > > completes. > > > > > > So I agree with the below if we suspect there could be pending PR, but > > > given that pending PR are a stop marker thing and we don't know any > > > device using stop markers, I wondered why I bothered implementing > > > PRIq flush at all for SMMUv3, hence this RFC. > > > > > > > Cheers, > > Ashok Thanks, Jacob ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [RFC PATCH 0/2] iommu: Avoid unnecessary PRI queue flushes
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. Thanks, Jean > > How does the driver know that everything host received has been responded > back to device? > > > > > > I'm not sure about other IOMMU's how they behave, When there is no space > > > in > > > the PRQ, IOMMU auto-responds to the device. This puts the device in a > > > while (1) loop. The fake successful response will let the device do a ATS > > > lookup, and that would fail forcing the device to do another PRQ. > > > > But in the sequence above, step 1 should ensure that the device will not > > send another PR for any successful response coming back at step 3. > > True, but there could be some page-request in flight on its way to the > IOMMU. By draining and getting that round trip back to IOMMU we gaurantee > things in flight are flushed to PRQ after that Drain completes. > > > > So I agree with the below if we suspect there could be pending PR, but > > given that pending PR are a stop marker thing and we don't know any device > > using stop markers, I wondered why I bothered implementing PRIq flush at > > all for SMMUv3, hence this RFC. > > > > Cheers, > Ashok ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [RFC PATCH 0/2] iommu: Avoid unnecessary PRI queue flushes
Hi Jean On Fri, Oct 16, 2020 at 09:59:23AM +0200, Jean-Philippe Brucker wrote: > On Thu, Oct 15, 2020 at 11:22:11AM -0700, Raj, Ashok wrote: > > Hi Jean > > > > + Baolu who is looking into this. > > > > > > On Thu, Oct 15, 2020 at 11:00:27AM +0200, Jean-Philippe Brucker wrote: > > > Add a parameter to iommu_sva_unbind_device() that tells the IOMMU driver > > > whether the PRI queue needs flushing. When looking at the PCIe spec > > > again I noticed that most of the time the SMMUv3 driver doesn't actually > > > need to flush the PRI queue. Does this make sense for Intel VT-d as well > > > or did I overlook something? > > > > > > Before calling iommu_sva_unbind_device(), device drivers must stop the > > > device from using the PASID. For PCIe devices, that consists of > > > completing any pending DMA, and completing any pending page request > > > unless the device uses Stop Markers. So unless the device uses Stop > > > Markers, we don't need to flush the PRI queue. For SMMUv3, stopping DMA > > > means completing all stall events, so we never need to flush the event > > > queue. > > > > I don't think this is true. Baolu is working on an enhancement to this, > > I'll quickly summarize this below: > > > > Stop markers are weird, I'm not certain there is any device today that > > sends STOP markers. Even if they did, markers don't have a required > > response, they are fire and forget from the device pov. > > Definitely agree with this, and I hope none will implement stop marker. > 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? How does the driver know that everything host received has been responded back to device? > > > I'm not sure about other IOMMU's how they behave, When there is no space in > > the PRQ, IOMMU auto-responds to the device. This puts the device in a > > while (1) loop. The fake successful response will let the device do a ATS > > lookup, and that would fail forcing the device to do another PRQ. > > But in the sequence above, step 1 should ensure that the device will not > send another PR for any successful response coming back at step 3. True, but there could be some page-request in flight on its way to the IOMMU. By draining and getting that round trip back to IOMMU we gaurantee things in flight are flushed to PRQ after that Drain completes. > > So I agree with the below if we suspect there could be pending PR, but > given that pending PR are a stop marker thing and we don't know any device > using stop markers, I wondered why I bothered implementing PRIq flush at > all for SMMUv3, hence this RFC. > Cheers, Ashok ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [RFC PATCH 0/2] iommu: Avoid unnecessary PRI queue flushes
On Thu, Oct 15, 2020 at 11:22:11AM -0700, Raj, Ashok wrote: > Hi Jean > > + Baolu who is looking into this. > > > On Thu, Oct 15, 2020 at 11:00:27AM +0200, Jean-Philippe Brucker wrote: > > Add a parameter to iommu_sva_unbind_device() that tells the IOMMU driver > > whether the PRI queue needs flushing. When looking at the PCIe spec > > again I noticed that most of the time the SMMUv3 driver doesn't actually > > need to flush the PRI queue. Does this make sense for Intel VT-d as well > > or did I overlook something? > > > > Before calling iommu_sva_unbind_device(), device drivers must stop the > > device from using the PASID. For PCIe devices, that consists of > > completing any pending DMA, and completing any pending page request > > unless the device uses Stop Markers. So unless the device uses Stop > > Markers, we don't need to flush the PRI queue. For SMMUv3, stopping DMA > > means completing all stall events, so we never need to flush the event > > queue. > > I don't think this is true. Baolu is working on an enhancement to this, > I'll quickly summarize this below: > > Stop markers are weird, I'm not certain there is any device today that > sends STOP markers. Even if they did, markers don't have a required > response, they are fire and forget from the device pov. Definitely agree with this, and I hope none will implement stop marker. 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. 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'm not sure about other IOMMU's how they behave, When there is no space in > the PRQ, IOMMU auto-responds to the device. This puts the device in a > while (1) loop. The fake successful response will let the device do a ATS > lookup, and that would fail forcing the device to do another PRQ. But in the sequence above, step 1 should ensure that the device will not send another PR for any successful response coming back at step 3. So I agree with the below if we suspect there could be pending PR, but given that pending PR are a stop marker thing and we don't know any device using stop markers, I wondered why I bothered implementing PRIq flush at all for SMMUv3, hence this RFC. Thanks, Jean > The idea > is somewhere there the OS has repeated the others and this will find a way > in the PRQ. The point is this is less reliable and can't be the only > indication. PRQ draining has a specific sequence. > > The detailed steps are outlined in > "Chapter 7.10 "Software Steps to Drain Page Requests & Responses" > > - Submit invalidation wait with fence flag to ensure all prior > invalidations are processed. > - submit iotlb followed by devtlb invalidation > - Submit invalidation wait with page-drain to make sure any page-requests > issued by the device are flushed when this invalidation wait completes. > - If during the above process there was a queue overflow SW can assume no > outstanding page-requests are there. If we had a queue full condition, > then sw must repeat step 2,3 above. > > > To that extent the proposal is as follows: names are suggestive :-) I'm > making this up as I go! > > - iommu_stop_page_req() - Kernel needs to make sure we respond to all > outstanding requests (since we can't drop responses) > - Ensure we respond immediatly for anything that comes before the drain > sequence completes > - iommu_drain_page_req() - Which does the above invalidation with > Page_drain set. > > Once the driver has performed a reset and before issuing any new request, > it does iommu_resume_page_req() this will ensure we start processing > incoming page-req after this point. > > > > > > First patch adds flags to unbind(), and the second one lets device > > drivers tell whether the PRI queue needs to be flushed. > > > > Other remarks: > > > > * The PCIe spec (see quote on patch 2), says that the device signals > > whether it has sent a Stop Marker or not during Stop PASID. In reality > > it's unlikely that a given device will sometimes use one stop method > > and sometimes the other, so it could be a device-wide flag rather than > > passing it at each unbind(). I don't want to speculate too much about > > future implementation so I prefer having the flag in unbind(). > > > > * In patch 1, uacce passes 0 to unbind(). To pass the right flag I'm > > thinking that uacce->ops->stop_queue(), which tells the device driver > > to stop DMA, should return
Re: [RFC PATCH 0/2] iommu: Avoid unnecessary PRI queue flushes
Hi Jean + Baolu who is looking into this. On Thu, Oct 15, 2020 at 11:00:27AM +0200, Jean-Philippe Brucker wrote: > Add a parameter to iommu_sva_unbind_device() that tells the IOMMU driver > whether the PRI queue needs flushing. When looking at the PCIe spec > again I noticed that most of the time the SMMUv3 driver doesn't actually > need to flush the PRI queue. Does this make sense for Intel VT-d as well > or did I overlook something? > > Before calling iommu_sva_unbind_device(), device drivers must stop the > device from using the PASID. For PCIe devices, that consists of > completing any pending DMA, and completing any pending page request > unless the device uses Stop Markers. So unless the device uses Stop > Markers, we don't need to flush the PRI queue. For SMMUv3, stopping DMA > means completing all stall events, so we never need to flush the event > queue. I don't think this is true. Baolu is working on an enhancement to this, I'll quickly summarize this below: Stop markers are weird, I'm not certain there is any device today that sends STOP markers. Even if they did, markers don't have a required response, they are fire and forget from the device pov. I'm not sure about other IOMMU's how they behave, When there is no space in the PRQ, IOMMU auto-responds to the device. This puts the device in a while (1) loop. The fake successful response will let the device do a ATS lookup, and that would fail forcing the device to do another PRQ. The idea is somewhere there the OS has repeated the others and this will find a way in the PRQ. The point is this is less reliable and can't be the only indication. PRQ draining has a specific sequence. The detailed steps are outlined in "Chapter 7.10 "Software Steps to Drain Page Requests & Responses" - Submit invalidation wait with fence flag to ensure all prior invalidations are processed. - submit iotlb followed by devtlb invalidation - Submit invalidation wait with page-drain to make sure any page-requests issued by the device are flushed when this invalidation wait completes. - If during the above process there was a queue overflow SW can assume no outstanding page-requests are there. If we had a queue full condition, then sw must repeat step 2,3 above. To that extent the proposal is as follows: names are suggestive :-) I'm making this up as I go! - iommu_stop_page_req() - Kernel needs to make sure we respond to all outstanding requests (since we can't drop responses) - Ensure we respond immediatly for anything that comes before the drain sequence completes - iommu_drain_page_req() - Which does the above invalidation with Page_drain set. Once the driver has performed a reset and before issuing any new request, it does iommu_resume_page_req() this will ensure we start processing incoming page-req after this point. > > First patch adds flags to unbind(), and the second one lets device > drivers tell whether the PRI queue needs to be flushed. > > Other remarks: > > * The PCIe spec (see quote on patch 2), says that the device signals > whether it has sent a Stop Marker or not during Stop PASID. In reality > it's unlikely that a given device will sometimes use one stop method > and sometimes the other, so it could be a device-wide flag rather than > passing it at each unbind(). I don't want to speculate too much about > future implementation so I prefer having the flag in unbind(). > > * In patch 1, uacce passes 0 to unbind(). To pass the right flag I'm > thinking that uacce->ops->stop_queue(), which tells the device driver > to stop DMA, should return whether faults are pending. This can be > added later once uacce has an actual PCIe user, but we need to > remember to do it. I think intel iommmu driver does this today for SVA when pasid is being freed. Its still important to go through the drain before that PASID can be re-purposed. Cheers, Ashok ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
[RFC PATCH 0/2] iommu: Avoid unnecessary PRI queue flushes
Add a parameter to iommu_sva_unbind_device() that tells the IOMMU driver whether the PRI queue needs flushing. When looking at the PCIe spec again I noticed that most of the time the SMMUv3 driver doesn't actually need to flush the PRI queue. Does this make sense for Intel VT-d as well or did I overlook something? Before calling iommu_sva_unbind_device(), device drivers must stop the device from using the PASID. For PCIe devices, that consists of completing any pending DMA, and completing any pending page request unless the device uses Stop Markers. So unless the device uses Stop Markers, we don't need to flush the PRI queue. For SMMUv3, stopping DMA means completing all stall events, so we never need to flush the event queue. First patch adds flags to unbind(), and the second one lets device drivers tell whether the PRI queue needs to be flushed. Other remarks: * The PCIe spec (see quote on patch 2), says that the device signals whether it has sent a Stop Marker or not during Stop PASID. In reality it's unlikely that a given device will sometimes use one stop method and sometimes the other, so it could be a device-wide flag rather than passing it at each unbind(). I don't want to speculate too much about future implementation so I prefer having the flag in unbind(). * In patch 1, uacce passes 0 to unbind(). To pass the right flag I'm thinking that uacce->ops->stop_queue(), which tells the device driver to stop DMA, should return whether faults are pending. This can be added later once uacce has an actual PCIe user, but we need to remember to do it. Jean-Philippe Brucker (2): iommu: Add flags to sva_unbind() iommu: Add IOMMU_UNBIND_FAULT_PENDING flag include/linux/intel-iommu.h | 2 +- include/linux/iommu.h | 38 ++--- drivers/iommu/intel/svm.c | 10 ++ drivers/iommu/iommu.c | 10 +++--- drivers/misc/uacce/uacce.c | 4 ++-- 5 files changed, 51 insertions(+), 13 deletions(-) -- 2.28.0 ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
