netdev - Re: Re: [RFC v4 05/11] vdpa: Support transferring virtual addressing during DMA mapping

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Message-ID: <CACycT3tFS=UOUqFKNP0R8fztymz+p9RP_d0843xDbVFd_govEw@mail.gmail.com>
Date:   Wed, 3 Mar 2021 20:45:38 +0800
From:   Yongji Xie <xieyongji@...edance.com>
To:     Mika Penttilä <mika.penttila@...tfour.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Parav Pandit <parav@...dia.com>, Bob Liu <bob.liu@...cle.com>,
        Christoph Hellwig <hch@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Matthew Wilcox <willy@...radead.org>, viro@...iv.linux.org.uk,
        Jens Axboe <axboe@...nel.dk>, bcrl@...ck.org,
        Jonathan Corbet <corbet@....net>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        kvm@...r.kernel.org, linux-aio@...ck.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: Re: [RFC v4 05/11] vdpa: Support transferring virtual addressing
 during DMA mapping

On Wed, Mar 3, 2021 at 6:52 PM Mika Penttilä <mika.penttila@...tfour.com> wrote:
>
>
>
> On 23.2.2021 13.50, Xie Yongji wrote:
> > This patch introduces an attribute for vDPA device to indicate
> > whether virtual address can be used. If vDPA device driver set
> > it, vhost-vdpa bus driver will not pin user page and transfer
> > userspace virtual address instead of physical address during
> > DMA mapping. And corresponding vma->vm_file and offset will be
> > also passed as an opaque pointer.
>
> In the virtual addressing case, who is then responsible for the pinning
> or even mapping physical pages to the vaddr?
>

Actually there's no need to pin the physical pages any more in this
case. The vDPA device should be able to access the user space memory
with virtual address if this attribute is set to true. For example, in
VDUSE case, we will make use of the vma->vm_file to support sharing
the memory between VM and VDUSE daemon.

Thanks,
Yongji