| Message ID | 1414572130-17014-2-git-send-email-clg@fr.ibm.com |
|---|---|
| State | New |
| Headers | show |
On Wed, 29 Oct 2014 09:42:09 +0100 Cédric Le Goater <clg@fr.ibm.com> wrote: > When the guest and the host have a different endian order, the data > being accessed in the vring queues needs to be byteswapped. > > This patch adds a VHOST_VRING_F_BYTESWAP flag to inform the vhost > kernel backend to byteswap vring data. > > Signed-off-by: Cédric Le Goater <clg@fr.ibm.com> > --- > hw/virtio/vhost.c | 25 ++++++++++++++++++++++++- > include/hw/virtio/vhost.h | 1 + > linux-headers/linux/vhost.h | 3 +++ > 3 files changed, 28 insertions(+), 1 deletion(-) > +static bool vhost_virtqueue_needs_byteswap(VirtIODevice *vdev) > +{ > +#ifdef TARGET_IS_BIENDIAN > +#ifdef HOST_WORDS_BIGENDIAN > + return !virtio_is_big_endian(vdev); > +#else > + return virtio_is_big_endian(vdev); > +#endif > + > +#else > + return false; > +#endif > +} *thinks aloud* We call this function after features have been negotiated, so we should be able to reuse this interface for virtio-1 by checking for VIRTIO_F_VERSION_1, right?
On Mon, 3 Nov 2014 16:29:31 +0100 Cornelia Huck <cornelia.huck@de.ibm.com> wrote: > On Wed, 29 Oct 2014 09:42:09 +0100 > Cédric Le Goater <clg@fr.ibm.com> wrote: > > > When the guest and the host have a different endian order, the data > > being accessed in the vring queues needs to be byteswapped. > > > > This patch adds a VHOST_VRING_F_BYTESWAP flag to inform the vhost > > kernel backend to byteswap vring data. > > > > Signed-off-by: Cédric Le Goater <clg@fr.ibm.com> > > --- > > hw/virtio/vhost.c | 25 ++++++++++++++++++++++++- > > include/hw/virtio/vhost.h | 1 + > > linux-headers/linux/vhost.h | 3 +++ > > 3 files changed, 28 insertions(+), 1 deletion(-) > > > +static bool vhost_virtqueue_needs_byteswap(VirtIODevice *vdev) > > +{ > > +#ifdef TARGET_IS_BIENDIAN > > +#ifdef HOST_WORDS_BIGENDIAN > > + return !virtio_is_big_endian(vdev); > > +#else > > + return virtio_is_big_endian(vdev); > > +#endif > > + > > +#else > > + return false; > > +#endif > > +} > > *thinks aloud* > > We call this function after features have been negotiated, so we should > be able to reuse this interface for virtio-1 by checking for > VIRTIO_F_VERSION_1, right? > > Yes. Moreover, we're not on a hot path, so we could simply ignore TARGET_IS_BIENDIAN and only have: static bool vhost_virtqueue_needs_byteswap(VirtIODevice *vdev) { #ifdef HOST_WORDS_BIGENDIAN return !virtio_is_big_endian(vdev); #else return virtio_is_big_endian(vdev); #endif } in which case, this would work right away with the changes brought by Conny's virtio-1 series: static inline bool virtio_device_is_legacy(VirtIODevice *vdev) { return !(vdev->guest_features[1] & (1 << (VIRTIO_F_VERSION_1 - 32))); } static inline bool virtio_is_big_endian(VirtIODevice *vdev) { if (virtio_device_is_legacy(vdev)) { assert(vdev->device_endian != VIRTIO_DEVICE_ENDIAN_UNKNOWN); return vdev->device_endian == VIRTIO_DEVICE_ENDIAN_BIG; } /* Devices conforming to VIRTIO 1.0 or later are always LE. */ return false; } Cheers. -- Greg
diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c index 5d7c40ac04d0..75308d127d90 100644 --- a/hw/virtio/vhost.c +++ b/hw/virtio/vhost.c @@ -539,7 +539,13 @@ static int vhost_virtqueue_set_addr(struct vhost_dev *dev, .log_guest_addr = vq->used_phys, .flags = enable_log ? (1 << VHOST_VRING_F_LOG) : 0, }; - int r = dev->vhost_ops->vhost_call(dev, VHOST_SET_VRING_ADDR, &addr); + int r; + + if (vq->byteswap) { + addr.flags |= (1 << VHOST_VRING_F_BYTESWAP); + } + + r = dev->vhost_ops->vhost_call(dev, VHOST_SET_VRING_ADDR, &addr); if (r < 0) { return -errno; } @@ -647,6 +653,21 @@ static void vhost_log_stop(MemoryListener *listener, /* FIXME: implement */ } + +static bool vhost_virtqueue_needs_byteswap(VirtIODevice *vdev) +{ +#ifdef TARGET_IS_BIENDIAN +#ifdef HOST_WORDS_BIGENDIAN + return !virtio_is_big_endian(vdev); +#else + return virtio_is_big_endian(vdev); +#endif + +#else + return false; +#endif +} + static int vhost_virtqueue_start(struct vhost_dev *dev, struct VirtIODevice *vdev, struct vhost_virtqueue *vq, @@ -707,6 +728,8 @@ static int vhost_virtqueue_start(struct vhost_dev *dev, goto fail_alloc_ring; } + vq->byteswap = vhost_virtqueue_needs_byteswap(vdev); + r = vhost_virtqueue_set_addr(dev, vq, vhost_vq_index, dev->log_enabled); if (r < 0) { r = -errno; diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h index d5593d162079..793f89d71ffb 100644 --- a/include/hw/virtio/vhost.h +++ b/include/hw/virtio/vhost.h @@ -20,6 +20,7 @@ struct vhost_virtqueue { unsigned long long ring_phys; unsigned ring_size; EventNotifier masked_notifier; + bool byteswap; }; typedef unsigned long vhost_log_chunk_t; diff --git a/linux-headers/linux/vhost.h b/linux-headers/linux/vhost.h index c656f61cfc75..0bbd3f1209f3 100644 --- a/linux-headers/linux/vhost.h +++ b/linux-headers/linux/vhost.h @@ -34,6 +34,9 @@ struct vhost_vring_addr { /* Flag values: */ /* Whether log address is valid. If set enables logging. */ #define VHOST_VRING_F_LOG 0 + /* Whether vring memory accesses should be byte-swapped. + * required when the guest has a different endianess */ +#define VHOST_VRING_F_BYTESWAP 1 /* Start of array of descriptors (virtually contiguous) */ __u64 desc_user_addr;
When the guest and the host have a different endian order, the data being accessed in the vring queues needs to be byteswapped. This patch adds a VHOST_VRING_F_BYTESWAP flag to inform the vhost kernel backend to byteswap vring data. Signed-off-by: Cédric Le Goater <clg@fr.ibm.com> --- hw/virtio/vhost.c | 25 ++++++++++++++++++++++++- include/hw/virtio/vhost.h | 1 + linux-headers/linux/vhost.h | 3 +++ 3 files changed, 28 insertions(+), 1 deletion(-)