Re: [PATCH] KVM: x86/mmu: Update number of zapped pages even if page list is stable

[Sean Christopherson]

On Thu, Nov 11, 2021, Ben Gardon wrote:
> On Thu, Nov 11, 2021 at 2:14 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
> > Fixes: fbb158cb88b6 ("KVM: x86/mmu: Revert "Revert "KVM: MMU: zap pages in batch""")
> > Reported-by: David Matlack <dmatlack@xxxxxxxxxx>
> > Cc: Ben Gardon <bgardon@xxxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> 
> Reviewed-by: Ben Gardon <bgardon@xxxxxxxxxx>
> 
> While I can see this fixing the above stall, there's still a potential
> issue where zapped_obsolete_pages can accumulate an arbitrary number
> of pages from multiple batches of zaps. If this list gets very large,
> we could see a stall after the loop while trying to free the pages.
> I'm not aware of this ever happening, but it could be worth yielding
> during that freeing process as well.

Ya.  I tagged this one for stable because its very much a regression that I
introduced when reverting the revert, i.e. the very original implemenation worked.
Sadly, I did not get to do a triple revert :-)