Linux Virtualization - Jul 2019 - [PATCH V2 4/9] vhost: reset invalidate_count in vhost_set_vring_num_addr()

On Wed, Jul 31, 2019 at 04:46:50AM -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 at redhat.com>
Did Michael report this as well?
> Fixes: 7f466032dc9e ("vhost: access vq metadata through kernel virtual
address")
> Signed-off-by: Jason Wang <jasowang at 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 2a3154976277..2a7217c33668 100644
> +++ b/drivers/vhost/vhost.c
> @@ -2073,6 +2073,10 @@ 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
>

On 2019/7/31 ??8:41, Jason Gunthorpe wrote:
> On Wed, Jul 31, 2019 at 04:46:50AM -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 at redhat.com>
> Did Michael report this as well?

Correct me if I was wrong. I think it's point 4 described in 
https://lkml.org/lkml/2019/7/21/25.

Thanks

>
>> Fixes: 7f466032dc9e ("vhost: access vq metadata through kernel
virtual address")
>> Signed-off-by: Jason Wang <jasowang at 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 2a3154976277..2a7217c33668 100644
>> +++ b/drivers/vhost/vhost.c
>> @@ -2073,6 +2073,10 @@ 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
>>

On Wed, Jul 31, 2019 at 09:29:28PM +0800, Jason Wang
wrote:
> 
> On 2019/7/31 ??8:41, Jason Gunthorpe wrote:
> > On Wed, Jul 31, 2019 at 04:46:50AM -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 at redhat.com>
> > Did Michael report this as well?
> 
> 
> Correct me if I was wrong. I think it's point 4 described in
> https://lkml.org/lkml/2019/7/21/25.
I'm not sure what that is talking about

But this fixes what I described:

https://lkml.org/lkml/2019/7/22/554

Jason