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Tsirkin" , qemu-devel@nongnu.org, =?UTF-8?Q?Eugenio_P=c3=a9rez?= , Eric Auger , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2020/6/28 下午10:47, Peter Xu wrote: > On Sun, Jun 28, 2020 at 03:03:41PM +0800, Jason Wang wrote: >> On 2020/6/27 上午5:29, Peter Xu wrote: >>> Hi, Eugenio, >>> >>> (CCing Eric, Yan and Michael too) >>> >>> On Fri, Jun 26, 2020 at 08:41:22AM +0200, Eugenio Pérez wrote: >>>> diff --git a/memory.c b/memory.c >>>> index 2f15a4b250..7f789710d2 100644 >>>> --- a/memory.c >>>> +++ b/memory.c >>>> @@ -1915,8 +1915,6 @@ void memory_region_notify_one(IOMMUNotifier *notifier, >>>> return; >>>> } >>>> - assert(entry->iova >= notifier->start && entry_end <= notifier->end); >>> I can understand removing the assertion should solve the issue, however imho >>> the major issue is not about this single assertion but the whole addr_mask >>> issue behind with virtio... >> >> I don't get here, it looks to the the range was from guest IOMMU drivers. > Yes. Note that I didn't mean that it's a problem in virtio, it's just the fact > that virtio is the only one I know that would like to support arbitrary address > range for the translated region. I don't know about tcg, but vfio should still > need some kind of page alignment in both the address and the addr_mask. We > have that assumption too across the memory core when we do translations. Right but it looks to me the issue is not the alignment. > > A further cause of the issue is the MSI region when vIOMMU enabled - currently > we implemented the interrupt region using another memory region so it split the > whole DMA region into two parts. That's really a clean approach to IR > implementation, however that's also a burden to the invalidation part because > then we'll need to handle things like this when the listened range is not page > alighed at all (neither 0-0xfedffff, nor 0xfef0000-MAX). If without the IR > region (so the whole iommu address range will be a single FlatRange), Is this a bug? I remember that at least for vtd, it won't do any DMAR on the intrrupt address range > I think > we probably don't need most of the logic in vtd_address_space_unmap() at all, > then we can directly deliver all the IOTLB invalidations without splitting into > small page aligned ranges to all the iommu notifiers. Sadly, so far I still > don't have ideal solution for it, because we definitely need IR. Another possible (theoretical) issue (for vhost) is that it can't trigger interrupt through the interrupt range. > >> >>> For normal IOTLB invalidations, we were trying our best to always make >>> IOMMUTLBEntry contain a valid addr_mask to be 2**N-1. E.g., that's what we're >>> doing with the loop in vtd_address_space_unmap(). >> >> I'm sure such such assumption can work for any type of IOMMU. >> >> >>> But this is not the first time that we may want to break this assumption for >>> virtio so that we make the IOTLB a tuple of (start, len), then that len can be >>> not a address mask any more. That seems to be more efficient for things like >>> vhost because iotlbs there are not page based, so it'll be inefficient if we >>> always guarantee the addr_mask because it'll be quite a lot more roundtrips of >>> the same range of invalidation. Here we've encountered another issue of >>> triggering the assertion with virtio-net, but only with the old RHEL7 guest. >>> >>> I'm thinking whether we can make the IOTLB invalidation configurable by >>> specifying whether the backend of the notifier can handle arbitary address >>> range in some way. So we still have the guaranteed addr_masks by default >>> (since I still don't think totally break the addr_mask restriction is wise...), >>> however we can allow the special backends to take adavantage of using arbitary >>> (start, len) ranges for reasons like performance. >>> >>> To do that, a quick idea is to introduce a flag IOMMU_NOTIFIER_ARBITRARY_MASK >>> to IOMMUNotifierFlag, to declare that the iommu notifier (and its backend) can >>> take arbitrary address mask, then it can be any value and finally becomes a >>> length rather than an addr_mask. Then for every iommu notify() we can directly >>> deliver whatever we've got from the upper layer to this notifier. With the new >>> flag, vhost can do iommu_notifier_init() with UNMAP|ARBITRARY_MASK so it >>> declares this capability. Then no matter for device iotlb or normal iotlb, we >>> skip the complicated procedure to split a big range into small ranges that are >>> with strict addr_mask, but directly deliver the message to the iommu notifier. >>> E.g., we can skip the loop in vtd_address_space_unmap() if the notifier is with >>> ARBITRARY flag set. >> >> I'm not sure coupling IOMMU capability to notifier is the best choice. > IMHO it's not an IOMMU capability. The flag I wanted to introduce is a > capability of the one who listens to the IOMMU TLB updates. For our case, it's > virtio/vhost's capability to allow arbitrary length. The IOMMU itself > definitely has some limitation on the address range to be bound to an IOTLB > invalidation, e.g., the device-iotlb we're talking here only accept both the > iova address and addr_mask to be aligned to 2**N-1. I think this go back to one of our previous discussion of whether to introduce a dedicated notifiers for device IOTLB. For IOMMU, it might have limitation like GAW, but for device IOTLB it probably doesn't. That's the reason we hit the assert here. > >> How about just convert to use a range [start, end] for any notifier and move >> the checks (e.g the assert) into the actual notifier implemented (vhost or >> vfio)? > IOMMUTLBEntry itself is the abstraction layer of TLB entry. Hardware TLB entry > is definitely not arbitrary range either (because AFAICT the hardware should > only cache PFN rather than address, so at least PAGE_SIZE aligned). > Introducing this flag will already make this trickier just to avoid introducing > another similar struct to IOMMUTLBEntry, but I really don't want to make it a > default option... Not to mention I probably have no reason to urge the rest > iommu notifier users (tcg, vfio) to change their existing good code to suite > any of the backend who can cooperate with arbitrary address ranges... Ok, so it looks like we need a dedicated notifiers to device IOTLB. Thanks > > Thanks, >