On Thu, Apr 11, 2024 at 06:55:44PM +0200, Paolo Bonzini wrote:

On Mon, Apr 8, 2024 at 3:56 PM Peter Xu [off-list ref] wrote:

quoted

Paolo,

I may miss a bunch of details here (as I still remember some change_pte
patches previously on the list..), however not sure whether we considered
enable it?  Asked because I remember Andrea used to have a custom tree
maintaining that part:

https://github.com/aagit/aa/commit/c761078df7a77d13ddfaeebe56a0f4bc128b1968

The patch enables it only for KSM, so it would still require a bunch
of cleanups, for example I also would still use set_pte_at() in all
the places that are not KSM. This would at least fix the issue with
the poor documentation of where to use set_pte_at_notify() vs
set_pte_at().

With regard to the implementation, I like the idea of disabling the
invalidation on the MMU notifier side, but I would rather have
MMU_NOTIFIER_CHANGE_PTE as a separate field in the range instead of
overloading the event field.

quoted

Maybe it can't be enabled for some reason that I overlooked in the current
tree, or we just decided to not to?

I have just learnt about the patch, nobody had ever mentioned it even
though it's almost 2 years old... It's a lot of code though and no one
has ever reported an issue for over 10 years, so I think it's easiest
to just rip the code out.

Right, it was pretty old and I have no idea if that was discussed or
published before..  It would be better to have discussed this earlier.

As long as we have a decision with that being aware and in mind, then it
looks fine to me to take either way to go, and I also agree either way is
better than keep the status quo.

I also have Andrea copied anyway when I replied, so I guess he should be
aware of this and he can chim in anytime.

Thanks!

-- 
Peter Xu