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Halil Pasic

2017-Jan-30 10:09 UTC

[PATCH] vhost: fix initialization for vq->is_le

Currently, under certain circumstances vhost_init_is_le does just a part
of the initialization job, and depends on vhost_reset_is_le being called
too. For this reason vhost_vq_init_access used to call vhost_reset_is_le
when vq->private_data is NULL. This is not only counter intuitive, but
also real a problem because it breaks vhost_net. The bug was introduced to
vhost_net with commit 2751c9882b94 ("vhost: cross-endian support for
legacy devices"). The symptom is corruption of the vq's used.idx field
(virtio) after VHOST_NET_SET_BACKEND was issued as a part of the vhost
shutdown on a vq with pending descriptors.

Let us make sure the outcome of vhost_init_is_le never depend on the state
it is actually supposed to initialize, and fix virtio_net by removing the
reset from vhost_vq_init_access.

With the above, there is no reason for vhost_reset_is_le to do just half
of the job. Let us make vhost_reset_is_le reinitialize is_le.

Signed-off-by: Halil Pasic <pasic at linux.vnet.ibm.com>
Reported-by: Michael A. Tebolt <miket at us.ibm.com>
Reported-by: Dr. David Alan Gilbert <dgilbert at redhat.com>
Fixes: commit 2751c9882b94 ("vhost: cross-endian support for legacy
devices")
---

The bug was already discussed here: 
http://www.spinics.net/lists/kvm/msg144365.html
This is a follow up patch.

---
 drivers/vhost/vhost.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index d643260..8f99fe0 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -130,14 +130,14 @@ static long vhost_get_vring_endian(struct vhost_virtqueue
*vq, u32 idx,
 
 static void vhost_init_is_le(struct vhost_virtqueue *vq)
 {
-	if (vhost_has_feature(vq, VIRTIO_F_VERSION_1))
-		vq->is_le = true;
+	vq->is_le = vhost_has_feature(vq, VIRTIO_F_VERSION_1)
+		|| virtio_legacy_is_little_endian();
 }
 #endif /* CONFIG_VHOST_CROSS_ENDIAN_LEGACY */
 
 static void vhost_reset_is_le(struct vhost_virtqueue *vq)
 {
-	vq->is_le = virtio_legacy_is_little_endian();
+	vhost_init_is_le(vq);
 }
 
 struct vhost_flush_struct {
@@ -1714,10 +1714,8 @@ int vhost_vq_init_access(struct vhost_virtqueue *vq)
 	int r;
 	bool is_le = vq->is_le;
 
-	if (!vq->private_data) {
-		vhost_reset_is_le(vq);
+	if (!vq->private_data)
 		return 0;
-	}
 
 	vhost_init_is_le(vq);
 
-- 
2.8.4

Greg Kurz

2017-Jan-30 19:06 UTC

head link

[PATCH] vhost: fix initialization for vq->is_le

On Mon, 30 Jan 2017 11:09:36 +0100
Halil Pasic <pasic at linux.vnet.ibm.com> wrote:
> Currently, under certain circumstances vhost_init_is_le does just a part
> of the initialization job, and depends on vhost_reset_is_le being called
> too. For this reason vhost_vq_init_access used to call vhost_reset_is_le
> when vq->private_data is NULL. This is not only counter intuitive, but
> also real a problem because it breaks vhost_net. The bug was introduced to
> vhost_net with commit 2751c9882b94 ("vhost: cross-endian support for
> legacy devices"). The symptom is corruption of the vq's used.idx
field
> (virtio) after VHOST_NET_SET_BACKEND was issued as a part of the vhost
> shutdown on a vq with pending descriptors.
> 
> Let us make sure the outcome of vhost_init_is_le never depend on the state
> it is actually supposed to initialize, and fix virtio_net by removing the
> reset from vhost_vq_init_access.
> 
> With the above, there is no reason for vhost_reset_is_le to do just half
> of the job. Let us make vhost_reset_is_le reinitialize is_le.
> 
> Signed-off-by: Halil Pasic <pasic at linux.vnet.ibm.com>
> Reported-by: Michael A. Tebolt <miket at us.ibm.com>
> Reported-by: Dr. David Alan Gilbert <dgilbert at redhat.com>
> Fixes: commit 2751c9882b94 ("vhost: cross-endian support for legacy
devices")
> ---
Reviewed-by: Greg Kurz <groug at kaod.org>
> 
> The bug was already discussed here: 
> http://www.spinics.net/lists/kvm/msg144365.html
> This is a follow up patch.
> 
> ---
>  drivers/vhost/vhost.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index d643260..8f99fe0 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -130,14 +130,14 @@ static long vhost_get_vring_endian(struct
vhost_virtqueue *vq, u32 idx,
>  
>  static void vhost_init_is_le(struct vhost_virtqueue *vq)
>  {
> -	if (vhost_has_feature(vq, VIRTIO_F_VERSION_1))
> -		vq->is_le = true;
> +	vq->is_le = vhost_has_feature(vq, VIRTIO_F_VERSION_1)
> +		|| virtio_legacy_is_little_endian();
>  }
>  #endif /* CONFIG_VHOST_CROSS_ENDIAN_LEGACY */
>  
>  static void vhost_reset_is_le(struct vhost_virtqueue *vq)
>  {
> -	vq->is_le = virtio_legacy_is_little_endian();
> +	vhost_init_is_le(vq);
>  }
>  
>  struct vhost_flush_struct {
> @@ -1714,10 +1714,8 @@ int vhost_vq_init_access(struct vhost_virtqueue *vq)
>  	int r;
>  	bool is_le = vq->is_le;
>  
> -	if (!vq->private_data) {
> -		vhost_reset_is_le(vq);
> +	if (!vq->private_data)
>  		return 0;
> -	}
>  
>  	vhost_init_is_le(vq);
>

Halil Pasic

2017-Jan-31 15:56 UTC

head link

[PATCH] vhost: fix initialization for vq->is_le

On 01/30/2017 08:06 PM, Greg Kurz wrote:>> Currently, under certain circumstances vhost_init_is_le does just a
part
>> of the initialization job, and depends on vhost_reset_is_le being
called
>> too. For this reason vhost_vq_init_access used to call
vhost_reset_is_le
>> when vq->private_data is NULL. This is not only counter intuitive,
but
>> also real a problem because it breaks vhost_net. The bug was introduced
to
>> vhost_net with commit 2751c9882b94 ("vhost: cross-endian support
for
>> legacy devices"). The symptom is corruption of the vq's
used.idx field
>> (virtio) after VHOST_NET_SET_BACKEND was issued as a part of the vhost
>> shutdown on a vq with pending descriptors.
>>
>> Let us make sure the outcome of vhost_init_is_le never depend on the
state
>> it is actually supposed to initialize, and fix virtio_net by removing
the
>> reset from vhost_vq_init_access.
>>
>> With the above, there is no reason for vhost_reset_is_le to do just
half
>> of the job. Let us make vhost_reset_is_le reinitialize is_le.
>>
>> Signed-off-by: Halil Pasic <pasic at linux.vnet.ibm.com>
>> Reported-by: Michael A. Tebolt <miket at us.ibm.com>
>> Reported-by: Dr. David Alan Gilbert <dgilbert at redhat.com>
>> Fixes: commit 2751c9882b94 ("vhost: cross-endian support for
legacy devices")
>> ---
> Reviewed-by: Greg Kurz <groug at kaod.org>
> 
Thanks! 

We have some tests on s390x (that is BE) running, but I won't be able to
test the change with cross endian and legacy. 

What do you think, should I/we RFT or are we fine without?

Regards,
Halil

Jason Wang

2017-Feb-04 02:27 UTC

head link

[PATCH] vhost: fix initialization for vq->is_le

On 2017?01?30? 18:09, Halil Pasic wrote:> Currently, under certain circumstances vhost_init_is_le does just a part
> of the initialization job, and depends on vhost_reset_is_le being called
> too. For this reason vhost_vq_init_access used to call vhost_reset_is_le
> when vq->private_data is NULL. This is not only counter intuitive, but
> also real a problem because it breaks vhost_net. The bug was introduced to
> vhost_net with commit 2751c9882b94 ("vhost: cross-endian support for
> legacy devices"). The symptom is corruption of the vq's used.idx
field
> (virtio) after VHOST_NET_SET_BACKEND was issued as a part of the vhost
> shutdown on a vq with pending descriptors.
>
> Let us make sure the outcome of vhost_init_is_le never depend on the state
> it is actually supposed to initialize, and fix virtio_net by removing the
> reset from vhost_vq_init_access.
>
> With the above, there is no reason for vhost_reset_is_le to do just half
> of the job. Let us make vhost_reset_is_le reinitialize is_le.
>
> Signed-off-by: Halil Pasic <pasic at linux.vnet.ibm.com>
> Reported-by: Michael A. Tebolt <miket at us.ibm.com>
> Reported-by: Dr. David Alan Gilbert <dgilbert at redhat.com>
> Fixes: commit 2751c9882b94 ("vhost: cross-endian support for legacy
devices")
> ---
>
> The bug was already discussed here:
> http://www.spinics.net/lists/kvm/msg144365.html
> This is a follow up patch.
>
> ---
>   drivers/vhost/vhost.c | 10 ++++------
>   1 file changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index d643260..8f99fe0 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -130,14 +130,14 @@ static long vhost_get_vring_endian(struct
vhost_virtqueue *vq, u32 idx,
>   
>   static void vhost_init_is_le(struct vhost_virtqueue *vq)
>   {
> -	if (vhost_has_feature(vq, VIRTIO_F_VERSION_1))
> -		vq->is_le = true;
> +	vq->is_le = vhost_has_feature(vq, VIRTIO_F_VERSION_1)
> +		|| virtio_legacy_is_little_endian();
>   }
>   #endif /* CONFIG_VHOST_CROSS_ENDIAN_LEGACY */
>   
>   static void vhost_reset_is_le(struct vhost_virtqueue *vq)
>   {
> -	vq->is_le = virtio_legacy_is_little_endian();
> +	vhost_init_is_le(vq);
>   }
>   
>   struct vhost_flush_struct {
> @@ -1714,10 +1714,8 @@ int vhost_vq_init_access(struct vhost_virtqueue *vq)
>   	int r;
>   	bool is_le = vq->is_le;
>   
> -	if (!vq->private_data) {
> -		vhost_reset_is_le(vq);
> +	if (!vq->private_data)
>   		return 0;
> -	}
>   
>   	vhost_init_is_le(vq);
>   
Acked-by: Jason Wang <jasowang at redhat.com>

We can probably just drop vhost_reset_is_le() and just use 
vhost_init_is_le() instead.

Thanks

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