From: Jason Wang <jasowang@redhat.com>
To: Peter Xu <peterx@redhat.com>
Cc: "Peter Maydell" <peter.maydell@linaro.org>,
"Yan Zhao" <yan.y.zhao@intel.com>,
"Juan Quintela" <quintela@redhat.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
qemu-devel@nongnu.org, "Eugenio Pérez" <eperezma@redhat.com>,
"Eric Auger" <eric.auger@redhat.com>,
"Paolo Bonzini" <pbonzini@redhat.com>
Subject: Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier
Date: Mon, 29 Jun 2020 13:51:47 +0800 [thread overview]
Message-ID: <54d2cdfd-97b8-9e1d-a607-d7a5e96be3a1@redhat.com> (raw)
In-Reply-To: <20200628144746.GA239443@xz-x1>
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,
>
next prev parent reply other threads:[~2020-06-29 5:53 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-26 6:41 [RFC v2 0/1] memory: Delete assertion in memory_region_unregister_iommu_notifier Eugenio Pérez
2020-06-26 6:41 ` [RFC v2 1/1] " Eugenio Pérez
2020-06-26 21:29 ` Peter Xu
2020-06-27 7:26 ` Yan Zhao
2020-06-27 12:57 ` Peter Xu
2020-06-28 1:36 ` Yan Zhao
2020-06-28 7:03 ` Jason Wang
2020-06-28 14:47 ` Peter Xu
2020-06-29 5:51 ` Jason Wang [this message]
2020-06-29 13:34 ` Peter Xu
2020-06-30 2:41 ` Jason Wang
2020-06-30 8:29 ` Jason Wang
2020-06-30 9:21 ` Michael S. Tsirkin
2020-06-30 9:23 ` Jason Wang
2020-06-30 15:20 ` Peter Xu
2020-07-01 8:11 ` Jason Wang
2020-07-01 12:16 ` Peter Xu
2020-07-01 12:30 ` Jason Wang
2020-07-01 12:41 ` Peter Xu
2020-07-02 3:00 ` Jason Wang
2020-06-30 15:39 ` Peter Xu
2020-07-01 8:09 ` Jason Wang
2020-07-02 3:01 ` Jason Wang
2020-07-02 15:45 ` Peter Xu
2020-07-03 7:24 ` Jason Wang
2020-07-03 13:03 ` Peter Xu
2020-07-07 8:03 ` Jason Wang
2020-07-07 19:54 ` Peter Xu
2020-07-08 5:42 ` Jason Wang
2020-07-08 14:16 ` Peter Xu
2020-07-09 5:58 ` Jason Wang
2020-07-09 14:10 ` Peter Xu
2020-07-10 6:34 ` Jason Wang
2020-07-10 13:30 ` Peter Xu
2020-07-13 4:04 ` Jason Wang
2020-07-16 1:00 ` Peter Xu
2020-07-16 2:54 ` Jason Wang
2020-07-17 14:18 ` Peter Xu
2020-07-20 4:02 ` Jason Wang
2020-07-20 13:03 ` Peter Xu
2020-07-21 6:20 ` Jason Wang
2020-07-21 15:10 ` Peter Xu
2020-08-03 16:00 ` Eugenio Pérez
2020-08-04 20:30 ` Peter Xu
2020-08-05 5:45 ` Jason Wang
2020-08-11 17:01 ` Eugenio Perez Martin
2020-08-11 17:10 ` Eugenio Perez Martin
2020-06-29 15:05 ` [RFC v2 0/1] " Paolo Bonzini
2020-07-03 7:39 ` Eugenio Perez Martin
2020-07-03 10:10 ` Paolo Bonzini
2020-08-11 17:55 ` [RFC v3 " Eugenio Pérez
2020-08-11 17:55 ` [RFC v3 1/1] memory: Skip bad range assertion if notifier supports arbitrary masks Eugenio Pérez
2020-08-12 2:24 ` Jason Wang
2020-08-12 8:49 ` Eugenio Perez Martin
2020-08-18 14:24 ` Eugenio Perez Martin
2020-08-19 7:15 ` Jason Wang
2020-08-19 8:22 ` Eugenio Perez Martin
2020-08-19 9:36 ` Jason Wang
2020-08-19 15:50 ` Peter Xu
2020-08-20 2:28 ` Jason Wang
2020-08-21 14:12 ` Peter Xu
2020-09-01 3:05 ` Jason Wang
2020-09-01 19:35 ` Peter Xu
2020-09-02 5:13 ` Jason Wang
2020-08-11 18:10 ` [RFC v3 0/1] memory: Delete assertion in memory_region_unregister_iommu_notifier Eugenio Perez Martin
2020-08-11 19:27 ` Peter Xu
2020-08-12 14:33 ` Eugenio Perez Martin
2020-08-12 21:12 ` Peter Xu
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