linux-kernel - Re: [PATCH v14 11/13] vduse: add vq group asid support

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Message-ID: <CACGkMEvJB5uyNnxmr=rap14Tc-JSy4=XGAtDZu6rg3+nucXUOw@mail.gmail.com>
Date: Mon, 19 Jan 2026 15:16:57 +0800
From: Jason Wang <jasowang@...hat.com>
To: Eugenio Pérez <eperezma@...hat.com>
Cc: "Michael S . Tsirkin" <mst@...hat.com>, Laurent Vivier <lvivier@...hat.com>, linux-kernel@...r.kernel.org, 
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Maxime Coquelin <mcoqueli@...hat.com>, 
	Cindy Lu <lulu@...hat.com>, virtualization@...ts.linux.dev, 
	Yongji Xie <xieyongji@...edance.com>, Stefano Garzarella <sgarzare@...hat.com>
Subject: Re: [PATCH v14 11/13] vduse: add vq group asid support

On Fri, Jan 16, 2026 at 10:05 PM Eugenio Pérez <eperezma@...hat.com> wrote:
>
> Add support for assigning Address Space Identifiers (ASIDs) to each VQ
> group.  This enables mapping each group into a distinct memory space.
>
> The vq group to ASID association is protected by a rwlock now.  But the
> mutex domain_lock keeps protecting the domains of all ASIDs, as some
> operations like the one related with the bounce buffer size still
> requires to lock all the ASIDs.
>
> Signed-off-by: Eugenio Pérez <eperezma@...hat.com>
>
> ---
> Future improvements can include performance optimizations on top like
> ore to RCU or thread synchronized atomics, or hardening by tracking ASID
> or ASID hashes on unused bits of the DMA address.
>
> Tested virtio_vdpa by adding manually two threads in vduse_set_status:
> one of them modifies the vq group 0 ASID and the other one map and unmap
> memory continuously.  After a while, the two threads stop and the usual
> work continues.  Test with version 0, version 1 with the old ioctl, and
> version 1 with the new ioctl.
>
> Tested with vhost_vdpa by migrating a VM while ping on OVS+VDUSE.  A few
> workaround were needed in some parts:
> * Do not enable CVQ before data vqs in QEMU, as VDUSE does not forward
>   the enable message to the userland device.  This will be solved in the
>   future.
> * Share the suspended state between all vhost devices in QEMU:
>   https://lists.nongnu.org/archive/html/qemu-devel/2025-11/msg02947.html
> * Implement a fake VDUSE suspend vdpa operation callback that always
>   returns true in the kernel.  DPDK suspend the device at the first
>   GET_VRING_BASE.
> * Remove the CVQ blocker in ASID.
>
> The driver vhost_vdpa was also tested with version 0, version 1 with the
> old ioctl, version 1 with the new ioctl but only one ASID, and version 1
> with many ASID.
>

Looks good overall, but I spot a small issue:

int vduse_domain_add_user_bounce_pages(struct vduse_iova_domain *domain,
                                       struct page **pages, int count)
{
        struct vduse_bounce_map *map, *head_map;
        ...

        /* Now we don't support partial mapping */
        if (count != (domain->bounce_size >> PAGE_SHIFT))
                return -EINVAL;

Here we still use domain->bounce_size even if we support multiple as,
this conflicts with the case without userspace memory.

Thanks