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

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Message-ID: <20201030161938.n7xqeu557dmsqpzv@steredhat>
Date:   Fri, 30 Oct 2020 17:19:38 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     mst@...hat.com, netdev@...r.kernel.org,
        Stefan Hajnoczi <stefanha@...hat.com>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vhost/vsock: add IOTLB API support

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.
>

I tried with "intel_iommu=strict" in the guest kernel and QEMU patch 
applied, but I didn't see any invalidation.

Maybe I did something wrong, you know it is friday, KVM Forum is ending, 
etc... ;-)

I'll investigate better next week.

Thanks for the useful info,
Stefano