Hi,
I have been looking at how we deal with page_count(page) on pages held
in stage 2 page tables on KVM/arm64.
What we do currently is to drop the reference on the page we get from
get_user_pages() once the page is inserted into our stage 2 page table,
typically leaving page_count(page) == page_mapcount(page) == 1 which
represents the userspace stage 1 mapping of the page,
and we rely on MMU notifiers to remove the stage 2 mapping if
corresponding stage 1 mapping is being unmapped.
I believe this is analogous to what other architectures do?
In some sense, we are thus maintaining a 'hidden', or internal,
reference to the page, which is not counted anywhere.
I am wondering if it would be equally valid to take a reference on the
page, and remove that reference when unmapping via MMU notifiers, and if
so, if there would be any advantages/drawbacks in doing so?
Thanks,
Christoffer
