mm: hugetlb: add huge page size param to set_huge_pte_at()

Patch series "Fix set_huge_pte_at() panic on arm64", v2.

This series fixes a bug in arm64's implementation of set_huge_pte_at(),
which can result in an unprivileged user causing a kernel panic.  The
problem was triggered when running the new uffd poison mm selftest for
HUGETLB memory.  This test (and the uffd poison feature) was merged for
v6.5-rc7.

Ideally, I'd like to get this fix in for v6.6 and I've cc'ed stable
(correctly this time) to get it backported to v6.5, where the issue first
showed up.


Description of Bug
------------------

arm64's huge pte implementation supports multiple huge page sizes, some of
which are implemented in the page table with multiple contiguous entries. 
So set_huge_pte_at() needs to work out how big the logical pte is, so that
it can also work out how many physical ptes (or pmds) need to be written. 
It previously did this by grabbing the folio out of the pte and querying
its size.

However, there are cases when the pte being set is actually a swap entry. 
But this also used to work fine, because for huge ptes, we only ever saw
migration entries and hwpoison entries.  And both of these types of swap
entries have a PFN embedded, so the code would grab that and everything
still worked out.

But over time, more calls to set_huge_pte_at() have been added that set
swap entry types that do not embed a PFN.  And this causes the code to go
bang.  The triggering case is for the uffd poison test, commit
99aa7721 ("selftests/mm: add uffd unit test for UFFDIO_POISON"), which
causes a PTE_MARKER_POISONED swap entry to be set, coutesey of commit
8a13897f ("mm: userfaultfd: support UFFDIO_POISON for hugetlbfs") -
added in v6.5-rc7.  Although review shows that there are other call sites
that set PTE_MARKER_UFFD_WP (which also has no PFN), these don't trigger
on arm64 because arm64 doesn't support UFFD WP.

If CONFIG_DEBUG_VM is enabled, we do at least get a BUG(), but otherwise,
it will dereference a bad pointer in page_folio():

    static inline struct folio *hugetlb_swap_entry_to_folio(swp_entry_t entry)
    {
        VM_BUG_ON(!is_migration_entry(entry) && !is_hwpoison_entry(entry));

        return page_folio(pfn_to_page(swp_offset_pfn(entry)));
    }


Fix