Re: [virtio-dev] [PATCH RFC 3/3] rng: leak detection support

[Babis Chalios <bchalios@amazon.es>]

>> yes, the queue switch is used as a barrier to detect a new leak event.
>
> Right, so I think that there is a race condition between the time the 
> driver sees the used buffers of the first
> batch and until it adds the second batch on the next leak queue.
>
> 1. driver adds batch 1
> 2. leak event
> 3. device uses batch 1
> 4. driver sees the used buffers and
>     a. switches leak queues
>     b. adds batch 2.
> 5. devices finds initial leak queue empty and sees buffers in second 
> leak queue.
>
> If a second leak event happens after step 3 above and before all of 
> steps 4 complete then batch 2 will not
> be processed as part of the second leak event.
>

Hey Michael, any thoughts on this? I think the my Linux RFC patch[1] 
showcases the problem in the
`entropy_leak_detected` function which handles the used buffers. If on 
the VMM we receive a new leak
event before `entropy_leak_detected` runs to completion (and adds a new 
batch of buffers) the leak
event will not have any buffers to handle.

[1] 
https://lore.kernel.org/lkml/20230823090107.65749-3-bchalios@amazon.es/T/#m085769c7b9c08f4acac626e7b4ecde11af13a5be

Cheers,
Babis

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