linux-kernel - Re: [RFC v2 4/7] vduse: return internal vq group struct as map token

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Message-ID: <CAJaqyWfh_3_J3+rq_7pa0YMUQSQHfeHn7Tvurz=PAmWoqV5vNg@mail.gmail.com>
Date: Mon, 11 Aug 2025 13:03:37 +0200
From: Eugenio Perez Martin <eperezma@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: "Michael S . Tsirkin" <mst@...hat.com>, Cindy Lu <lulu@...hat.com>, 
	Yongji Xie <xieyongji@...edance.com>, Stefano Garzarella <sgarzare@...hat.com>, 
	virtualization@...ts.linux.dev, Laurent Vivier <lvivier@...hat.com>, 
	linux-kernel@...r.kernel.org, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, 
	Maxime Coquelin <mcoqueli@...hat.com>
Subject: Re: [RFC v2 4/7] vduse: return internal vq group struct as map token

On Mon, Aug 11, 2025 at 5:11 AM Jason Wang <jasowang@...hat.com> wrote:
>
> On Thu, Aug 7, 2025 at 7:58 PM Eugenio Pérez <eperezma@...hat.com> wrote:
> >
> > Return the internal struct that represents the vq group as virtqueue map
> > token, instead of the device.
>
> Note that Michael prefers to use the iova domain. This indeed seems to
> be better.
>

Well iova domain would delete an indirection in the pointer chase, but
it would be problematic to store the token in the caller.

And we need to add some way to protect that the ASID of a vq group is
not changed in the middle of the operation by an ioctl. IOW, the
vq_group_internal struct pointer is constant for all the lifetime of
the device, while iova_domain is not.

> > This allows the DMA functions to access
>
> s/DMA/map/
>

Ouch, thanks for the catch!

> > the information per group.
> >
> > At this moment all the virtqueues share the same vq group, that only
> > can point to ASID 0.  This change prepares the infrastructure for actual
> > per-group address space handling
> >
> > Signed-off-by: Eugenio Pérez <eperezma@...hat.com>
>
> Thanks
>