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Re: [PATCH] vhost: Unbreak SMMU and virtio-iommu on dev-iotlb support
From: |
Auger Eric |
Subject: |
Re: [PATCH] vhost: Unbreak SMMU and virtio-iommu on dev-iotlb support |
Date: |
Mon, 8 Feb 2021 21:23:48 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 |
Hi,
On 2/7/21 3:47 PM, Peter Xu wrote:
> Hi, Kevin,
>
> On Sun, Feb 07, 2021 at 09:04:55AM +0000, Tian, Kevin wrote:
>>> From: Peter Xu
>>> Sent: Friday, February 5, 2021 11:31 PM
>>>
>>>>>
>>>>>
>>>>>> or virtio-iommu
>>>>>> since dev-iotlb (or PCIe ATS)
>>>>>
>>>>>
>>>>> We may need to add this in the future.
>>>> added Jean-Philippe in CC
>>>
>>> So that's the part I'm unsure about.. Since everybody is cced so maybe good
>>> time to ask. :)
>>>
>>> The thing is I'm still not clear on whether dev-iotlb is useful for a full
>>> emulation environment and how that should differ from a normal iotlb, since
>>> after all normal iotlb will be attached with device information too.
>>
>> dev-iotlb is useful in two manners.First, it's a functional prerequisite for
>> supporting I/O page faults.
If I understand correctly, the stall model of the ARM SMMU allows IOPF I
guess without dev-iotlb (ATS). However indeed PRI requires ATS.
>
> Is this also a hard requirement for virtio-iommu, which is not a real hardware
> after all?
>
>> Second, it has performance benefit as you don't
>> need to contend the lock of global iotlb.
>
> Hmm.. are you talking about e.g. vt-d driver or virtio-iommu?
>
> Assuming it's about vt-d, qi_flush_dev_iotlb() will still call
> qi_submit_sync()
> and taking the same global QI lock, as I see it, or I could be wrong
> somewhere.
> I don't see where dev-iotlb has a standalone channel for delivery.
>
> For virtio-iommu, we haven't defined dev-iotlb, right?
no there is no such feature at the moment. If my understanding is
correct this would only make sense when protecting a HW device. In that
case the underlying physical IOMMU would be programmed for ATS.
When protecting a virtio device (inc. vhost) what would be the adventage
over the current standard unmap notifier?
Thanks
Eric
Sorry I missed things
> when I completely didn't follow virtio-iommu recently - let's say if
> virtio-iommu in the future can support per-dev dev-iotlb queue so it doesn't
> need a global lock, what if we make it still per-device but still delivering
> iotlb message? Again, it's still a bit unclear to me why a full emulation
> iommu would need that definition of "iotlb" and "dev-iotlb".
>
>>
>>>
>>> For real hardwares, they make sense because they ask for two things: iotlb
>>> is
>>> for IOMMU, but dev-iotlb is for the device cache. For emulation
>>> environment
>>> (virtio-iommu is the case) do we really need that complexity?
>>>
>>> Note that even if there're assigned devices under virtio-iommu in the
>>> future,
>>> we can still isolate that and iiuc we can easily convert an iotlb (from
>>> virtio-iommu) into a hardware IOMMU dev-iotlb no matter what type of
>>> IOMMU is
>>> underneath the vIOMMU.
>>>
>>
>> Didn't get this point. Hardware dev-iotlb is updated by hardware (between
>> the device and the IOMMU). How could software convert a virtual iotlb
>> entry into hardware dev-iotlb?
>
> I mean if virtio-iommu must be run in a guest, then we can trap that message
> first, right? If there're assigned device in the guest, we must convert that
> invalidation to whatever message required for the host, that seems to not
> require the virtio-iommu to have dev-iotlb knowledge, still?
>
> Thanks,
>
- [PATCH] vhost: Unbreak SMMU and virtio-iommu on dev-iotlb support, Peter Xu, 2021/02/04
- Re: [PATCH] vhost: Unbreak SMMU and virtio-iommu on dev-iotlb support, Jason Wang, 2021/02/04
- Re: [PATCH] vhost: Unbreak SMMU and virtio-iommu on dev-iotlb support, Auger Eric, 2021/02/05
- Re: [PATCH] vhost: Unbreak SMMU and virtio-iommu on dev-iotlb support, Peter Xu, 2021/02/05
- RE: [PATCH] vhost: Unbreak SMMU and virtio-iommu on dev-iotlb support, Tian, Kevin, 2021/02/07
- Re: [PATCH] vhost: Unbreak SMMU and virtio-iommu on dev-iotlb support, Peter Xu, 2021/02/07
- RE: [PATCH] vhost: Unbreak SMMU and virtio-iommu on dev-iotlb support, Tian, Kevin, 2021/02/08
- Re: [PATCH] vhost: Unbreak SMMU and virtio-iommu on dev-iotlb support, Peter Xu, 2021/02/08
- Re: [PATCH] vhost: Unbreak SMMU and virtio-iommu on dev-iotlb support, Jason Wang, 2021/02/09
- Re: [PATCH] vhost: Unbreak SMMU and virtio-iommu on dev-iotlb support,
Auger Eric <=
- Re: [PATCH] vhost: Unbreak SMMU and virtio-iommu on dev-iotlb support, Jason Wang, 2021/02/07
- Re: [PATCH] vhost: Unbreak SMMU and virtio-iommu on dev-iotlb support, Peter Xu, 2021/02/08
- Re: [PATCH] vhost: Unbreak SMMU and virtio-iommu on dev-iotlb support, Auger Eric, 2021/02/08
- Re: [PATCH] vhost: Unbreak SMMU and virtio-iommu on dev-iotlb support, Jason Wang, 2021/02/08
- Re: [PATCH] vhost: Unbreak SMMU and virtio-iommu on dev-iotlb support, Auger Eric, 2021/02/09
- Re: [PATCH] vhost: Unbreak SMMU and virtio-iommu on dev-iotlb support, Peter Xu, 2021/02/09