On 07.08.24 11:17, Claudio Imbrenda wrote:
On Fri, 2 Aug 2024 17:55:15 +0200
David Hildenbrand <david@xxxxxxxxxx> wrote:
We want to get rid of follow_page(), and have a more reasonable way to
just lookup a folio mapped at a certain address, perform some checks while
still under PTL, and then only conditionally grab a folio reference if
really required.
Further, we might want to get rid of some walk_page_range*() users that
really only want to temporarily lookup a single folio at a single address.
So let's add a new page table walker that does exactly that, similarly
to GUP also being able to walk hugetlb VMAs.
Add folio_walk_end() as a macro for now: the compiler is not easy to
please with the pte_unmap()->kunmap_local().
Note that one difference between follow_page() and get_user_pages(1) is
that follow_page() will not trigger faults to get something mapped. So
folio_walk is at least currently not a replacement for get_user_pages(1),
but could likely be extended/reused to achieve something similar in the
future.
[...]
+pmd_table:
+ VM_WARN_ON_ONCE(pud_leaf(*pudp));
Thanks for the review!
is this warning necessary? can this actually happen?
and if it can happen, wouldn't it be more reasonable to return NULL?
The we have to turn this into an unconditional WARN_ON_ONCE() that
cannot be compiled out.
It's something that should be found early during testing (like I had a
bug where I misspelled "CONFIG_PGTABLE_HAS_HUGE_LEAVES" above that took
me 2h to debug, so I added it ;) ), and shouldn't need runtime checks.
Same for the other one.
Thanks!
--
Cheers,
David / dhildenb
