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

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Message-ID: <CAJaqyWf_37cwV6mK-_nj4GnwquSxUYCPFKUOkxCaPQkJ9iewLQ@mail.gmail.com>
Date: Mon, 19 Jan 2026 09:09:38 +0100
From: Eugenio Perez Martin <eperezma@...hat.com>
To: Jason Wang <jasowang@...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 Mon, Jan 19, 2026 at 8:17 AM Jason Wang <jasowang@...hat.com> wrote:
>
> 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.
>

I don't follow you. My understanding from the previous discussion is
that the bounce size is distributed evenly per AS. Should we just have
a global bounce buffer size and protect that the amount of added
memory of all domains is less than that bounce size?