Re: [PATCH] tcm_vhost: Avoid VIRTIO_RING_F_EVENT_IDX feature bit

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Mar 28, 2013 at 12:27:10AM +0000, Nicholas A. Bellinger wrote:
> 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>

No chance we can debug this properly?

> ---
>  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)

All the rest of the code uses VHOST_SCSI so rename this too?

> +};
> +

Please do something like

+/*
+* VIRTIO_RING_F_EVENT_IDX seems broken. Not sure the bug is in
+* kernel but disabling it helps.
+* TODO: debug and remove the workaround.
+*/
+enum {
+     VHOST_SCSI_FEATURES = VHOST_FEATURES & (~VIRTIO_RING_F_EVENT_IDX)
+}

>  #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