linux-kernel - Re: [PATCH] xen: don't require virtio with grants for non-PV guests

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Message-ID: <Yqnh7vjO8iT4/fiK@infradead.org>
Date:   Wed, 15 Jun 2022 06:43:10 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Juergen Gross <jgross@...e.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        xen-devel@...ts.xenproject.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
Subject: Re: [PATCH] xen: don't require virtio with grants for non-PV guests

On Wed, Jun 15, 2022 at 02:53:54PM +0200, Juergen Gross wrote:
> On 15.06.22 13:54, Christoph Hellwig wrote:
> > On Wed, Jun 15, 2022 at 01:39:01PM +0200, Juergen Gross wrote:
> > > No, it doesn't. I'm working on a qemu patch series enabling the qemu
> > > based backends to support grants with virtio. The code is working fine
> > > on x86, too (apart from the fact that the backends aren't ready yet).
> > 
> > The code right now in mainline only ever sets the ops for DMA.  So
> > I can't see how you could make it work.
> 
> Ah, you are right. I was using a guest with an older version of the series.
> Sorry for the noise.

No problem.  But whatever you end up using to enable the grant DMA
ops n x86 should also require the platform access feature.  We already
have that information so we can make use of it.