[4/6] vhost: reset invalidate_count in vhost_set_vring_num_addr()
diff mbox series

Message ID 20190723075718.6275-5-jasowang@redhat.com
State New
Headers show
Series
  • Fixes for meta data acceleration
Related show

Commit Message

Jason Wang July 23, 2019, 7:57 a.m. UTC
The vhost_set_vring_num_addr() could be called in the middle of
invalidate_range_start() and invalidate_range_end(). If we don't reset
invalidate_count after the un-registering of MMU notifier, the
invalidate_cont will run out of sync (e.g never reach zero). This will
in fact disable the fast accessor path. Fixing by reset the count to
zero.

Reported-by: Michael S. Tsirkin <mst@redhat.com>
Fixes: 7f466032dc9e ("vhost: access vq metadata through kernel virtual address")
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 drivers/vhost/vhost.c | 4 ++++
 1 file changed, 4 insertions(+)

Comments

Michael S. Tsirkin July 23, 2019, 9:17 a.m. UTC | #1
On Tue, Jul 23, 2019 at 03:57:16AM -0400, Jason Wang wrote:
> The vhost_set_vring_num_addr() could be called in the middle of
> invalidate_range_start() and invalidate_range_end(). If we don't reset
> invalidate_count after the un-registering of MMU notifier, the
> invalidate_cont will run out of sync (e.g never reach zero). This will
> in fact disable the fast accessor path. Fixing by reset the count to
> zero.
> 
> Reported-by: Michael S. Tsirkin <mst@redhat.com>
> Fixes: 7f466032dc9e ("vhost: access vq metadata through kernel virtual address")
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
>  drivers/vhost/vhost.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 03666b702498..89c9f08b5146 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -2074,6 +2074,10 @@ static long vhost_vring_set_num_addr(struct vhost_dev *d,
>  		d->has_notifier = false;
>  	}
>  
> +	/* reset invalidate_count in case we are in the middle of
> +	 * invalidate_start() and invalidate_end().
> +	 */
> +	vq->invalidate_count = 0;

I think that the code is ok but the comments are not very clear:
- we are never in the middle since we just removed the notifier
- the result is not just disabling optimization:
  if notifier becomes negative, then later we
  can think it's ok to map when it isn't since
  notifier is active.

>  	vhost_uninit_vq_maps(vq);
>  #endif
>  
> -- 
> 2.18.1
Jason Wang July 23, 2019, 1:25 p.m. UTC | #2
On 2019/7/23 下午5:17, Michael S. Tsirkin wrote:
> On Tue, Jul 23, 2019 at 03:57:16AM -0400, Jason Wang wrote:
>> The vhost_set_vring_num_addr() could be called in the middle of
>> invalidate_range_start() and invalidate_range_end(). If we don't reset
>> invalidate_count after the un-registering of MMU notifier, the
>> invalidate_cont will run out of sync (e.g never reach zero). This will
>> in fact disable the fast accessor path. Fixing by reset the count to
>> zero.
>>
>> Reported-by: Michael S. Tsirkin <mst@redhat.com>
>> Fixes: 7f466032dc9e ("vhost: access vq metadata through kernel virtual address")
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>> ---
>>   drivers/vhost/vhost.c | 4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>> index 03666b702498..89c9f08b5146 100644
>> --- a/drivers/vhost/vhost.c
>> +++ b/drivers/vhost/vhost.c
>> @@ -2074,6 +2074,10 @@ static long vhost_vring_set_num_addr(struct vhost_dev *d,
>>   		d->has_notifier = false;
>>   	}
>>   
>> +	/* reset invalidate_count in case we are in the middle of
>> +	 * invalidate_start() and invalidate_end().
>> +	 */
>> +	vq->invalidate_count = 0;
> I think that the code is ok but the comments are not very clear:
> - we are never in the middle since we just removed the notifier


If I read the code correctly, mmu_notifier_unregister() can only 
guarantee to wait for the pending method to complete. So we can have:

invalidate_start()

mmu_notifier_unregister()

invalidate_end()


> - the result is not just disabling optimization:
>    if notifier becomes negative, then later we
>    can think it's ok to map when it isn't since
>    notifier is active.


I don't get how it could be negative, the only possible thing is to have 
a positive value.

Thanks


>
>>   	vhost_uninit_vq_maps(vq);
>>   #endif
>>   
>> -- 
>> 2.18.1

Patch
diff mbox series

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 03666b702498..89c9f08b5146 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2074,6 +2074,10 @@  static long vhost_vring_set_num_addr(struct vhost_dev *d,
 		d->has_notifier = false;
 	}
 
+	/* reset invalidate_count in case we are in the middle of
+	 * invalidate_start() and invalidate_end().
+	 */
+	vq->invalidate_count = 0;
 	vhost_uninit_vq_maps(vq);
 #endif