linux-kernel - Re: [PATCH v2] vhost/vsock: add IOTLB API support

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Message-ID: <20210104101952.GA344891@stefanha-x1.localdomain>
Date:   Mon, 4 Jan 2021 10:19:52 +0000
From:   Stefan Hajnoczi <stefanha@...il.com>
To:     Stefano Garzarella <sgarzare@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        "Michael S. Tsirkin" <mst@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Stefan Hajnoczi <stefanha@...hat.com>
Subject: Re: [PATCH v2] vhost/vsock: add IOTLB API support

On Wed, Dec 23, 2020 at 03:36:38PM +0100, 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 specifying "intel_iommu=strict" in the guest
> kernel command line. I used QEMU with a patch applied [1] to fix a
> simple issue (that patch was merged in QEMU v5.2.0):
>     $ qemu -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=3,iommu_platform=on,ats=on
> 
> [1] https://lists.gnu.org/archive/html/qemu-devel/2020-10/msg09077.html
> 
> Reviewed-by: Stefan Hajnoczi <stefanha@...hat.com>
> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
> ---
> 
> The patch is the same of v1, but I re-tested it with:
> - QEMU v5.2.0-551-ga05f8ecd88
> - Linux 5.9.15 (host)
> - Linux 5.9.15 and 5.10.0 (guest)
> Now, enabling 'ats' it works well, there are just a few simple changes.
> 
> v1: https://www.spinics.net/lists/kernel/msg3716022.html
> v2:
> - updated commit message about QEMU version and string used to test
> - rebased on mst/vhost branch
> 
> Thanks,
> Stefano
> ---
>  drivers/vhost/vsock.c | 68 +++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 65 insertions(+), 3 deletions(-)

Acked-by: Stefan Hajnoczi <stefanha@...hat.com>

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