Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Mon, 7 Dec 2020 14:48:38 +0000
From:   Stefan Hajnoczi <stefanha@gmail.com>
To:     David Hildenbrand <david@redhat.com>
Cc:     Peter Xu <peterx@redhat.com>,
        Stefan Hajnoczi <stefanha@redhat.com>,
        Justin He <Justin.He@arm.com>,
        Alex Williamson <alex.williamson@redhat.com>,
        Cornelia Huck <cohuck@redhat.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] vfio iommu type1: Bypass the vma permission check in
 vfio_pin_pages_remote()
Message-ID: <20201207144838.GG203660@stefanha-x1.localdomain>
References: <20201119142737.17574-1-justin.he@arm.com>
 <20201124181228.GA276043@xz-x1>
 <AM6PR08MB32245E7F990955395B44CE6BF7FA0@AM6PR08MB3224.eurprd08.prod.outlook.com>
 <20201125155711.GA6489@xz-x1>
 <20201202143356.GK655829@stefanha-x1.localdomain>
 <20201202154511.GI3277@xz-x1>
 <20201203112002.GE689053@stefanha-x1.localdomain>
 <20201203154322.GH108496@xz-x1>
 <6a33e908-17ff-7a26-7341-4bcf7bbefe28@redhat.com>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha256;
        protocol="application/pgp-signature"; boundary="yZnyZsPjQYjG7xG7"
Content-Disposition: inline
In-Reply-To: <6a33e908-17ff-7a26-7341-4bcf7bbefe28@redhat.com>
Precedence: bulk


--yZnyZsPjQYjG7xG7
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline

On Thu, Dec 03, 2020 at 05:01:32PM +0100, David Hildenbrand wrote:
> The real question is: do we even *need* DMA from vfio devices to
> virtio-fs regions? If not (do guests rely on it? what does the spec
> state?), just don't care about vfio at all and don't map anything.

Can DMA to/from the virtio-fs DAX Window happen? Yes, the guest could do
it although it's rare.

Is it a great idea to combine VFIO and virtio-fs DAX? Maybe not. It
involves pinning host page cache pages O_o.

Stefan

--yZnyZsPjQYjG7xG7
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----

iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAl/OQMUACgkQnKSrs4Gr
c8jT2Af+JXkEPTuSerosjvKJgxGcKudB8C6f/Okm8J3Ylryh+5QznpspkUcnzDUe
DokGkgjxcA6sqSsEMGqwSGLS3Ozshm9sUGRK4GAZsblxWDS9a5Es5A9SQvh117ip
PED58xmoIHuFhoMIkzo/BrBvVzRFX/x4q7VEredEv23pAvlNWIRQm60DsgULcqiU
1EEbA+Hl8w0s4PYEYOw7suFUI3+lDB/0oOd9+YXl9UyV7guC7jaGJg+gQX7mVBi2
fnTlX/JeigsKT/DcwMFmlMtvw0emRYtfIOtubsT/k2eYM+5Az9OTzWqNF+33sJhe
fGup4va8T0HHYPiOwaKu+QrFfwDgHw==
=gJnL
-----END PGP SIGNATURE-----

--yZnyZsPjQYjG7xG7--