Re: [PATCH 2/2] kvm: clear dirty bitmaps from all overlapping memslots

[Paolo Bonzini]

On 20/09/19 14:18, Peter Xu wrote:
>   (1) memory region aliasing, hence multiple GPAs can point to the same
>       HVA/HPA so we need to clear the memslot dirty bits on all the
>       mapped GPAs, and,
> 
>   (2) large log_clear() request which can cover more than one valid
>       kvm memslots.  Note that in this case, the mem slots can really
>       be having different HVAs so imho it should be a different issue
>       comparing to (1)
> 
> The commit message says it's solving problem (1).  However for what I
> understand, we are actually doing well on issue (1) because in
> memory_region_clear_dirty_bitmap() we iterate over all the flat views
> so that we should have caught all the aliasing memory regions if there
> are any.

There could be two addresses pointing to the same HVA *in the same
flatview*.  See for example 0xe0000..0xfffff and 0xffffe000..0xffffffff
when a PC guest is started.  In this particular case
0xffffe000..0xffffffff is ROM, so it's not an issue, but in other cases
it may

> However this patch should perfectly fix problem (2).  Am I right?

I hadn't thought of problem (2).  I guess without Igor's work for s390
it does not exist?  But yes, it fixes it just the same.

Paolo