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

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Message-ID: <aad1b7a9-0a3b-6220-06e1-bc4a3e2b59ed@nextfour.com>
Date:   Wed, 3 Mar 2021 15:38:39 +0200
From:   Mika Penttilä <mika.penttila@...tfour.com>
To:     Yongji Xie <xieyongji@...edance.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: [RFC v4 05/11] vdpa: Support transferring virtual addressing
 during DMA mapping



On 3.3.2021 14.45, Yongji Xie wrote:
> 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
Ah ok you have a shared file pointer + offset.

thanks,
Mika