linux-kernel - [PATCH RFC don't apply] vdpa_sim: endian-ness for config space

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Message-ID: <20200715135540.22832-1-mst@redhat.com>
Date:   Wed, 15 Jul 2020 09:58:08 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org
Subject: [PATCH RFC don't apply] vdpa_sim: endian-ness for config space

VDPA sim stores config space as native endian, but that
is wrong: modern guests expect LE.
I coded up the following to fix it up, but it is wrong too:
vdpasim_create is called before guest features are known.

So what should we do? New ioctl to specify the interface used?
More ideas?

Signed-off-by: Michael S. Tsirkin <mst@...hat.com>


---
 drivers/vdpa/vdpa_sim/vdpa_sim.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
index a9bc5e0fb353..cc754ae0ec15 100644
--- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
+++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
@@ -24,6 +24,7 @@
 #include <linux/etherdevice.h>
 #include <linux/vringh.h>
 #include <linux/vdpa.h>
+#include <linux/virtio_byteorder.h>
 #include <linux/vhost_iotlb.h>
 #include <uapi/linux/virtio_config.h>
 #include <uapi/linux/virtio_net.h>
@@ -72,6 +73,23 @@ struct vdpasim {
 	u64 features;
 };
 
+/* TODO: cross-endian support */
+static inline bool vdpasim_is_little_endian(struct vdpasim *vdpasim)
+{
+	return virtio_legacy_is_little_endian() ||
+		(vdpasim->features & (1ULL << VIRTIO_F_VERSION_1));
+}
+
+static inline u16 vdpasim16_to_cpu(struct vdpasim *vdpasim, __virtio16 val)
+{
+	return __virtio16_to_cpu(vdpasim_is_little_endian(vdpasim), val);
+}
+
+static inline __virtio16 cpu_to_vdpasim16(struct vdpasim *vdpasim, u16 val)
+{
+	return __cpu_to_virtio16(vdpasim_is_little_endian(vdpasim), val);
+}
+
 static struct vdpasim *vdpasim_dev;
 
 static struct vdpasim *vdpa_to_sim(struct vdpa_device *vdpa)
@@ -332,8 +350,8 @@ static struct vdpasim *vdpasim_create(void)
 		goto err_iommu;
 
 	config = &vdpasim->config;
-	config->mtu = 1500;
-	config->status = VIRTIO_NET_S_LINK_UP;
+	config->mtu = cpu_to_vdpasim16(vdpasim, 1500);
+	config->status = cpu_to_vdpasim16(vdpasim, VIRTIO_NET_S_LINK_UP);
 	eth_random_addr(config->mac);
 
 	vringh_set_iotlb(&vdpasim->vqs[0].vring, vdpasim->iommu);
-- 
MST