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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 2020/6/29 下午9:34, Peter Xu wrote: > On Mon, Jun 29, 2020 at 01:51:47PM +0800, Jason Wang wrote: >> 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 don't think it's a bug, at least it's working as how I understand... that > interrupt range is using an IR region, that's why I said the IR region splits > the DMAR region into two pieces, so we have two FlatRange for the same > IOMMUMemoryRegion. I don't check the qemu code but if "a single FlatRange" means 0xFEEx_xxxx is subject to DMA remapping, OS need to setup passthrough mapping for that range in order to get MSI to work. This is not what vtd spec said: """ 3.14 Handling Requests to Interrupt Address Range Requests without PASID to address range 0xFEEx_xxxx are treated as potential interrupt requests and are not subjected to DMA remapping (even if translation structures specify a mapping for this range). Instead, remapping hardware can be enabled to subject such interrupt requests to interrupt remapping. """ My understanding is vtd won't do any DMA translation on 0xFEEx_xxxx even if IR is not enabled. > >> >>> 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. > Hmm.. Could you explain? When IR is enabled, all devices including virtio > who send interrupt to 0xfeeXXXXX should be trapped by IR. I meant vhost not virtio, if you teach vhost to DMA to 0xFEEx_xxxx, it can't generate any interrupts as expected. > >> >>>>> 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. > I feel like even for hardware it shouldn't be arbitrary either, Yes, but from the view of IOMMU, it's hard to know about that. Allowing [0, ~0ULL] looks sane. > because the > device iotlb sent from at least vt-d driver is very restricted too (borrowing > the comment you wrote :): > > /* According to ATS spec table 2.4: > * S = 0, bits 15:12 = xxxx range size: 4K > * S = 1, bits 15:12 = xxx0 range size: 8K > * S = 1, bits 15:12 = xx01 range size: 16K > * S = 1, bits 15:12 = x011 range size: 32K > * S = 1, bits 15:12 = 0111 range size: 64K > * ... > */ Right, but the comment is probably misleading here, since it's for the PCI-E transaction between IOMMU and device not for the device IOTLB invalidation descriptor. For device IOTLB invalidation descriptor, spec allows a [0, ~0ULL] invalidation: " 6.5.2.5 Device-TLB Invalidate Descriptor ... Size (S): The size field indicates the number of consecutive pages targeted by this invalidation request. If S field is zero, a single page at page address specified by Address [63:12] is requested to be invalidated. If S field is Set, the least significant bit in the Address field with value 0b indicates the invalidation address range. For example, if S field is Set and Address[12] is Clear, it indicates an 8KB invalidation address range with base address in Address [63:13]. If S field and Address[12] is Set and bit 13 is Clear, it indicates a 16KB invalidation address range with base address in Address [63:14], etc. " So if we receive an address whose [63] is 0 and the rest is all 1, it's then a [0, ~0ULL] invalidation. > >> >>>> 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. > Or we can also make a new flag for device iotlb just like current UNMAP? Then > we replace the vhost type from UNMAP to DEVICE_IOTLB. But IMHO using the > ARBITRARY_LENGTH flag would work in a similar way. DEVICE_IOTLB flag could > also allow virtio/vhost to only receive one invalidation (now IIUC it'll > receive both iotlb and device-iotlb for unmapping a page when ats=on), but then > ats=on will be a must and it could break some old (misconfiged) qemu because > afaict previously virtio/vhost could even work with vIOMMU (accidentally) even > without ats=on. That's a bug and I don't think we need to workaround mis-configurated qemu :) Thanks > > Thanks, >