[PATCH] tcm_vhost: Avoid VIRTIO_RING_F_EVENT_IDX feature bit

["Nicholas A. Bellinger" <nab@linux-iscsi.org>]

From: Nicholas Bellinger <nab@linux-iscsi.org>

This patch adds a VHOST_TCM_FEATURES mask minus VIRTIO_RING_F_EVENT_IDX
so that vhost-scsi-pci userspace will strip this feature bit once
GET_FEATURES reports it as being unsupported on the host.

This is to avoid a bug where ->handle_kicks() are missed when EVENT_IDX
is enabled by default in userspace code.

Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Asias He <asias@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
---
 drivers/vhost/tcm_vhost.c |   10 ++++++++--
 1 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/tcm_vhost.c b/drivers/vhost/tcm_vhost.c
index 0524267..b127edc 100644
--- a/drivers/vhost/tcm_vhost.c
+++ b/drivers/vhost/tcm_vhost.c
@@ -60,6 +60,12 @@ enum {
 	VHOST_SCSI_VQ_IO = 2,
 };
 
+enum {
+	VHOST_TCM_FEATURES = (1ULL << VIRTIO_F_NOTIFY_ON_EMPTY) |
+			     (1ULL << VIRTIO_RING_F_INDIRECT_DESC) |
+			     (1ULL << VHOST_F_LOG_ALL)
+};
+
 #define VHOST_SCSI_MAX_TARGET	256
 #define VHOST_SCSI_MAX_VQ	128
 
@@ -981,7 +987,7 @@ static void vhost_scsi_flush(struct vhost_scsi *vs)
 
 static int vhost_scsi_set_features(struct vhost_scsi *vs, u64 features)
 {
-	if (features & ~VHOST_FEATURES)
+	if (features & ~VHOST_TCM_FEATURES)
 		return -EOPNOTSUPP;
 
 	mutex_lock(&vs->dev.mutex);
@@ -1027,7 +1033,7 @@ static long vhost_scsi_ioctl(struct file *f, unsigned int ioctl,
 			return -EFAULT;
 		return 0;
 	case VHOST_GET_FEATURES:
-		features = VHOST_FEATURES;
+		features = VHOST_TCM_FEATURES;
 		if (copy_to_user(featurep, &features, sizeof features))
 			return -EFAULT;
 		return 0;
-- 
1.7.2.5