Re: Re: [RFC PATCH V2 0/7] Do not read from descripto ring

From: Jason Wang <jasowang@redhat.com>
To: Yongji Xie <xieyongji@bytedance.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	virtualization <virtualization@lists.linux-foundation.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	file@sect.tu-berlin.de, ashish.kalra@amd.com,
	konrad.wilk@oracle.com, kvm <kvm@vger.kernel.org>,
	Christoph Hellwig <hch@infradead.org>
Subject: Re: Re: [RFC PATCH V2 0/7] Do not read from descripto ring
Date: Fri, 14 May 2021 15:30:52 +0800	[thread overview]
Message-ID: <CACGkMEvKByPZFwN8bU6_SfRbS9i43am7X5WGJQtE=Yh+YKWOHw@mail.gmail.com> (raw)
In-Reply-To: <CACycT3v-2naEaXEtPqaKcGz8qpfnmp4VzrHefqLNhO=9=57jdQ@mail.gmail.com>

On Fri, May 14, 2021 at 2:07 PM Yongji Xie <xieyongji@bytedance.com> wrote:
>
> On Fri, May 14, 2021 at 12:27 AM Stefan Hajnoczi <stefanha@redhat.com> wrote:
> >
> > On Fri, Apr 23, 2021 at 04:09:35PM +0800, Jason Wang wrote:
> > > Sometimes, the driver doesn't trust the device. This is usually
> > > happens for the encrtpyed VM or VDUSE[1].
> >
> > Thanks for doing this.
> >
> > Can you describe the overall memory safety model that virtio drivers
> > must follow? For example:
> >
> > - Driver-to-device buffers must be on dedicated pages to avoid
> >   information leaks.
> >
> > - Driver-to-device buffers must be on dedicated pages to avoid memory
> >   corruption.
> >
> > When I say "pages" I guess it's the IOMMU page size that matters?
> >
> > What is the memory access granularity of VDUSE?
> >
>
> Now we use PAGE_SIZE as the access granularity. I think it should be
> safe to access the Driver-to-device buffers in VDUSE case because we
> also use bounce-buffering mechanism like swiotlb does.
>
> Thanks,
> Yongji
>

Yes, while at this, I wonder it's possible the re-use the swiotlb
codes for VDUSE, or having some common library for this. Otherwise
there would be duplicated codes (bugs).

Thanks