Re: [PATCH] vhost/vsock: add IOTLB API support

Jason Wang
2020-11-03T09:05:16Z

On 2020/11/3 上午1:11, Stefano Garzarella wrote:
> On Fri, Oct 30, 2020 at 07:44:43PM +0800, Jason Wang wrote:
>>
>> On 2020/10/30 下午6:54, Stefano Garzarella wrote:
>>> On Fri, Oct 30, 2020 at 06:02:18PM +0800, Jason Wang wrote:
>>>>
>>>> On 2020/10/30 上午1:43, Stefano Garzarella wrote:
>>>>> This patch enables the IOTLB API support for vhost-vsock devices,
>>>>> allowing the userspace to emulate an IOMMU for the guest.
>>>>>
>>>>> These changes were made following vhost-net, in details this patch:
>>>>> - exposes VIRTIO_F_ACCESS_PLATFORM feature and inits the iotlb
>>>>>   device if the feature is acked
>>>>> - implements VHOST_GET_BACKEND_FEATURES and
>>>>>   VHOST_SET_BACKEND_FEATURES ioctls
>>>>> - calls vq_meta_prefetch() before vq processing to prefetch vq
>>>>>   metadata address in IOTLB
>>>>> - provides .read_iter, .write_iter, and .poll callbacks for the
>>>>>   chardev; they are used by the userspace to exchange IOTLB messages
>>>>>
>>>>> This patch was tested with QEMU and a patch applied [1] to fix a
>>>>> simple issue:
>>>>>     $ qemu -M q35,accel=kvm,kernel-irqchip=split \
>>>>>            -drive file=fedora.qcow2,format=qcow2,if=virtio \
>>>>>            -device intel-iommu,intremap=on \
>>>>>            -device vhost-vsock-pci,guest-cid=3,iommu_platform=on
>>>>
>>>>
>>>> Patch looks good, but a question:
>>>>
>>>> It looks to me you don't enable ATS which means vhost won't get any
>>>> invalidation request or did I miss anything?
>>>>
>>>
>>> You're right, I didn't see invalidation requests, only miss and
>>> updates.
>>> Now I have tried to enable 'ats' and 'device-iotlb' but I still
>>> don't see any invalidation.
>>>
>>> How can I test it? (Sorry but I don't have much experience yet with
>>> vIOMMU)
>>
>>
>> I guess it's because the batched unmap. Maybe you can try to use
>> "intel_iommu=strict" in guest kernel command line to see if it works.
>>
>> Btw, make sure the qemu contains the patch [1]. Otherwise ATS won't
>> be enabled for recent Linux Kernel in the guest.
>
> The problem was my kernel, it was built with a tiny configuration.
> Using fedora stock kernel I can see the 'invalidate' requests, but I
> also had the following issues.
>
> Do they make you ring any bells?
>
> $ ./qemu -m 4G -smp 4 -M q35,accel=kvm,kernel-irqchip=split \
>     -drive file=fedora.qcow2,format=qcow2,if=virtio \
>     -device intel-iommu,intremap=on,device-iotlb=on \
>     -device vhost-vsock-pci,guest-cid=6,iommu_platform=on,ats=on,id=v1
>
>     qemu-system-x86_64: vtd_iova_to_slpte: detected IOVA overflow
> (iova=0x1d40000030c0)

It's a hint that IOVA exceeds the AW. It might be worth to check whether
the missed IOVA reported from IOTLB is legal.

Thanks

> qemu-system-x86_64: vtd_iommu_translate: detected translation failure
> (dev=00:03:00, iova=0x1d40000030c0)
>     qemu-system-x86_64: New fault is not recorded due to compression
> of     faults
>
> Guest kernel messages:
>     [   44.940872] DMAR: DRHD: handling fault status reg 2
>     [   44.941989] DMAR: [DMA Read] Request device [00:03.0] PASID
> ffffffff fault addr ffff88W
>     [   49.785884] DMAR: DRHD: handling fault status reg 2
>     [   49.788874] DMAR: [DMA Read] Request device [00:03.0] PASID
> ffffffff fault addr ffff88W
>
>
> QEMU: b149dea55c Merge remote-tracking branch
> 'remotes/cschoenebeck/tags/pull-9p-20201102' into staging
>
> Linux guest: 5.8.16-200.fc32.x86_64
>
>
> Thanks,
> Stefano
>