From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH 2/3] vhost: add support for legacy virtio Date: Sun, 22 Feb 2015 10:48:29 +0100 Message-ID: <20150222094829.GB17529@redhat.com> References: <20150220100724.18608.74654.stgit@bahia.local> <20150220100746.18608.15083.stgit@bahia.local> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Cedric Le Goater , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org To: Greg Kurz Return-path: Received: from mx1.redhat.com ([209.132.183.28]:36841 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751308AbbBVJsj (ORCPT ); Sun, 22 Feb 2015 04:48:39 -0500 Content-Disposition: inline In-Reply-To: <20150220100746.18608.15083.stgit@bahia.local> Sender: kvm-owner@vger.kernel.org List-ID: On Fri, Feb 20, 2015 at 11:14:47AM +0100, Greg Kurz wrote: > Signed-off-by: Greg Kurz > --- > drivers/vhost/vhost.h | 20 ++++++++++++++------ > 1 file changed, 14 insertions(+), 6 deletions(-) > > Michael, > > The vhost_is_little_endian() helper adds unconditionnal overhead to fixed > endian architectures: that is all architectures except arm and ppc64. This > was addressed in QEMU with a TARGET_IS_BIENDIAN macro. Please give an > advice about how to address this in the vhost code. > > Thanks. I suggest creating a config option for this, default to off. When disabled the flag won't be set so userspace can discover it's availability. > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h > index ce2c68e..21e7d6a 100644 > --- a/drivers/vhost/vhost.h > +++ b/drivers/vhost/vhost.h > @@ -176,34 +176,42 @@ static inline bool vhost_has_feature(struct vhost_virtqueue *vq, int bit) > return vq->acked_features & (1ULL << bit); > } > > +static inline bool vhost_is_little_endian(struct vhost_virtqueue *vq) > +{ > + if (vhost_has_feature(vq, VIRTIO_F_VERSION_1)) > + return true; > + else > + return !vq->legacy_big_endian; > +} > + > /* Memory accessors */ > static inline u16 vhost16_to_cpu(struct vhost_virtqueue *vq, __virtio16 val) > { > - return __virtio16_to_cpu(vhost_has_feature(vq, VIRTIO_F_VERSION_1), val); > + return __virtio16_to_cpu(vhost_is_little_endian(vq), val); > } > > static inline __virtio16 cpu_to_vhost16(struct vhost_virtqueue *vq, u16 val) > { > - return __cpu_to_virtio16(vhost_has_feature(vq, VIRTIO_F_VERSION_1), val); > + return __cpu_to_virtio16(vhost_is_little_endian(vq), val); > } > > static inline u32 vhost32_to_cpu(struct vhost_virtqueue *vq, __virtio32 val) > { > - return __virtio32_to_cpu(vhost_has_feature(vq, VIRTIO_F_VERSION_1), val); > + return __virtio32_to_cpu(vhost_is_little_endian(vq), val); > } > > static inline __virtio32 cpu_to_vhost32(struct vhost_virtqueue *vq, u32 val) > { > - return __cpu_to_virtio32(vhost_has_feature(vq, VIRTIO_F_VERSION_1), val); > + return __cpu_to_virtio32(vhost_is_little_endian(vq), val); > } > > static inline u64 vhost64_to_cpu(struct vhost_virtqueue *vq, __virtio64 val) > { > - return __virtio64_to_cpu(vhost_has_feature(vq, VIRTIO_F_VERSION_1), val); > + return __virtio64_to_cpu(vhost_is_little_endian(vq), val); > } > > static inline __virtio64 cpu_to_vhost64(struct vhost_virtqueue *vq, u64 val) > { > - return __cpu_to_virtio64(vhost_has_feature(vq, VIRTIO_F_VERSION_1), val); > + return __cpu_to_virtio64(vhost_is_little_endian(vq), val); > } > #endif