Re: [PATCH v2 00/20] Introduce the TDP MMU

[Paolo Bonzini]

On 19/10/20 20:15, Ben Gardon wrote:
> When getting the dirty log, we
> follow the following steps:
> 1. Atomically get and clear an unsigned long of the dirty bitmap
> 2. For each GFN in the range of pages covered by the unsigned long mask:
>     3. Clear the dirty or writable bit on the SPTE
> 4. Copy the mask of dirty pages to be returned to userspace
> 
> If we mark the page as dirty in the dirty bitmap in step 3, we'll
> report the page as dirty twice - once in this dirty log call, and
> again in the next one. This can lead to unexpected behavior:
> 1. Pause all vCPUs
> 2. Get the dirty log <--- Returns all pages dirtied before the vCPUs were paused
> 3. Get the dirty log again <--- Unexpectedly returns a non-zero number
> of dirty pages even though no pages were actually dirtied

Got it, that might also fail the dirty_log_test.  Thanks!

Paolo