Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753014AbcDUO5B (ORCPT ); Thu, 21 Apr 2016 10:57:01 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43219 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752945AbcDUO44 (ORCPT ); Thu, 21 Apr 2016 10:56:56 -0400 Date: Thu, 21 Apr 2016 15:56:53 +0100 From: Stefan Hajnoczi To: "Michael S. Tsirkin" Cc: qemu-devel@nongnu.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com, peterx@redhat.com, cornelia.huck@de.ibm.com, Kevin Wolf , Amit Shah , qemu-block@nongnu.org, Jason Wang , Alex Williamson , Andy Lutomirski , Christian Borntraeger , Wei Liu , David Woodhouse , virtualization@lists.linux-foundation.org, kvm@vger.kernel.org Subject: Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api Message-ID: <20160421145653.GB11814@stefanha-x1.localdomain> References: <1461245745-6710-1-git-send-email-mst@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="eAbsdosE1cNLO4uF" Content-Disposition: inline In-Reply-To: <1461245745-6710-1-git-send-email-mst@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4446 Lines: 112 --eAbsdosE1cNLO4uF Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Apr 21, 2016 at 04:43:45PM +0300, Michael S. Tsirkin wrote: > This adds a flag to enable/disable bypassing the IOMMU by > virtio devices. >=20 > This is on top of patch > http://article.gmane.org/gmane.comp.emulators.qemu/403467 > virtio: convert to use DMA api >=20 > Tested with patchset > http://article.gmane.org/gmane.linux.kernel.virtualization/27545 > virtio-pci: iommu support (note: bit number has been kept at 34 > intentionally to match posted guest code. a non-RFC version will > renumber bits to be contigious). >=20 > changes from v1: > drop PASSTHROUGH flag >=20 > The interaction between virtio and DMA API is messy. >=20 > On most systems with virtio, physical addresses match bus addresses, > and it doesn't particularly matter whether we use the DMA API. >=20 > On some systems, including Xen and any system with a physical device > that speaks virtio behind a physical IOMMU, we must use the DMA API > for virtio DMA to work at all. >=20 > Add a feature bit to detect that: VIRTIO_F_IOMMU_PLATFORM. >=20 > If not there, we preserve historic behavior and bypass the DMA > API unless within Xen guest. This is actually required for > systems, including SPARC and PPC64, where virtio-pci devices are > enumerated as though they are behind an IOMMU, but the virtio host > ignores the IOMMU, so we must either pretend that the IOMMU isn't > there or somehow map everything as the identity. >=20 > Re: non-virtio devices. >=20 > It turns out that on old QEMU hosts, only emulated devices which were > part of QEMU use the IOMMU. Should we want to bypass the IOMMU for such > devices *only*, it would be rather easy to detect them by looking at > subsystem vendor and device ID. Thus, no new interfaces are required > except for virtio which always uses the same subsystem vendor and device = ID. >=20 > Signed-off-by: Michael S. Tsirkin > --- > include/hw/virtio/virtio-access.h | 3 ++- > include/hw/virtio/virtio.h | 4 +++- > include/standard-headers/linux/virtio_config.h | 2 ++ > 3 files changed, 7 insertions(+), 2 deletions(-) >=20 > diff --git a/include/hw/virtio/virtio-access.h b/include/hw/virtio/virtio= -access.h > index 967cc75..bb6f34e 100644 > --- a/include/hw/virtio/virtio-access.h > +++ b/include/hw/virtio/virtio-access.h > @@ -23,7 +23,8 @@ static inline AddressSpace *virtio_get_dma_as(VirtIODev= ice *vdev) > BusState *qbus =3D qdev_get_parent_bus(DEVICE(vdev)); > VirtioBusClass *k =3D VIRTIO_BUS_GET_CLASS(qbus); > =20 > - if (k->get_dma_as) { > + if (virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM) && > + k->get_dma_as) { > return k->get_dma_as(qbus->parent); > } > return &address_space_memory; > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h > index b12faa9..44f3788 100644 > --- a/include/hw/virtio/virtio.h > +++ b/include/hw/virtio/virtio.h > @@ -228,7 +228,9 @@ typedef struct VirtIORNGConf VirtIORNGConf; > DEFINE_PROP_BIT64("notify_on_empty", _state, _field, \ > VIRTIO_F_NOTIFY_ON_EMPTY, true), \ > DEFINE_PROP_BIT64("any_layout", _state, _field, \ > - VIRTIO_F_ANY_LAYOUT, true) > + VIRTIO_F_ANY_LAYOUT, true), \ > + DEFINE_PROP_BIT64("iommu_platform", _state, _field, \ > + VIRTIO_F_IOMMU_PLATFORM, false) Looks like the impact of this patch is that users who relied on k->get_dma_as today may now have to explicitly add iommu_platform=3Don. Are there any such users (e.g. Xen)? Instead of breaking the command-line for these users you could invert the flag's meaning ("iommu_bypass=3Don") and set it in the SPARC/PPC machine types. Stefan --eAbsdosE1cNLO4uF Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQEcBAEBAgAGBQJXGOo1AAoJEJykq7OBq3PI7lwH/2t5PRCwZwvZeBX4nAsVWabI bYmZTMkQ8hIUXkhdc0GF+bq7+ToxRHLcpI+jxkO6czY69ws/ynVozNireneLk0Hy mOPQcTz/vvTLLGCAMS/gilEwDIjyaC+5/F2uwwVoEIj6Ug99WqXMrk3fpl27WGdc W8MotOICwLU+/1zRm4CZ8a09d+LZXNQ3L3J8Lb3nvRkiTtPszsTrmEfe8TNxhuf2 eWR20e4l8E27di+vja0lRlF080HbWTfwGbf1I6WMZmFMkF1Mdoa00pD23JD/AVqE kWcSMHMHR/3gwBW6oLJzuvrzizcF7frx0VxI6dCFJvzHAR/tczB/jpnMq6BEnSo= =+QU1 -----END PGP SIGNATURE----- --eAbsdosE1cNLO4uF--