The patch titled Subject: arm64: hugetlb: fix set_huge_pte_at() to work with all swap entries has been added to the -mm mm-hotfixes-unstable branch. Its filename is arm64-hugetlb-fix-set_huge_pte_at-to-work-with-all-swap-entries.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Ryan Roberts ryan.roberts@arm.com Subject: arm64: hugetlb: fix set_huge_pte_at() to work with all swap entries Date: Fri, 22 Sep 2023 12:58:04 +0100

When called with a swap entry that does not embed a PFN (e.g. PTE_MARKER_POISONED or PTE_MARKER_UFFD_WP), the previous implementation of set_huge_pte_at() would either cause a BUG() to fire (if CONFIG_DEBUG_VM is enabled) or cause a dereference of an invalid address and subsequent panic.

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 99aa77215ad0 ("selftests/mm: add uffd unit test for UFFDIO_POISON"), which causes a PTE_MARKER_POISONED swap entry to be set, coutesey of commit 8a13897fb0da ("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.

Arguably, the root cause is really due to commit 18f3962953e4 ("mm: hugetlb: kill set_huge_swap_pte_at()"), which aimed to simplify the interface to the core code by removing set_huge_swap_pte_at() (which took a page size parameter) and replacing it with calls to set_huge_pte_at() where the size was inferred from the folio, as descibed above. While that commit didn't break anything at the time, it did break the interface because it couldn't handle swap entries without PFNs. And since then new callers have come along which rely on this working. But given the brokeness is only observable after commit 8a13897fb0da ("mm: userfaultfd: support UFFDIO_POISON for hugetlbfs"), that one gets the Fixes tag.

Now that we have modified the set_huge_pte_at() interface to pass the huge page size in the previous patch, we can trivially fix this issue.

Link: https://lkml.kernel.org/r/20230922115804.2043771-3-ryan.roberts@arm.com Fixes: 8a13897fb0da ("mm: userfaultfd: support UFFDIO_POISON for hugetlbfs") Signed-off-by: Ryan Roberts ryan.roberts@arm.com Cc: Albert Ou aou@eecs.berkeley.edu Cc: Alexander Gordeev agordeev@linux.ibm.com Cc: Alexandre Ghiti alex@ghiti.fr Cc: Anshuman Khandual anshuman.khandual@arm.com Cc: Arnd Bergmann arnd@arndb.de Cc: Axel Rasmussen axelrasmussen@google.com Cc: Catalin Marinas catalin.marinas@arm.com Cc: Christian Borntraeger borntraeger@linux.ibm.com Cc: Christophe Leroy christophe.leroy@csgroup.eu Cc: Christoph Hellwig hch@infradead.org Cc: David S. Miller davem@davemloft.net Cc: Gerald Schaefer gerald.schaefer@linux.ibm.com Cc: Heiko Carstens hca@linux.ibm.com Cc: Helge Deller deller@gmx.de Cc: "James E.J. Bottomley" James.Bottomley@HansenPartnership.com Cc: Lorenzo Stoakes lstoakes@gmail.com Cc: Mike Kravetz mike.kravetz@oracle.com Cc: Muchun Song muchun.song@linux.dev Cc: Nicholas Piggin npiggin@gmail.com Cc: Palmer Dabbelt palmer@dabbelt.com Cc: Paul Walmsley paul.walmsley@sifive.com Cc: Peter Xu peterx@redhat.com Cc: Qi Zheng zhengqi.arch@bytedance.com Cc: SeongJae Park sj@kernel.org Cc: Sven Schnelle svens@linux.ibm.com Cc: Uladzislau Rezki (Sony) urezki@gmail.com Cc: Vasily Gorbik gor@linux.ibm.com Cc: Will Deacon will@kernel.org Cc: stable@vger.kernel.org [6.5+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

arch/arm64/mm/hugetlbpage.c | 17 +++-------------- 1 file changed, 3 insertions(+), 14 deletions(-)

--- a/arch/arm64/mm/hugetlbpage.c~arm64-hugetlb-fix-set_huge_pte_at-to-work-with-all-swap-entries +++ a/arch/arm64/mm/hugetlbpage.c @@ -241,13 +241,6 @@ static void clear_flush(struct mm_struct flush_tlb_range(&vma, saddr, addr); }

-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))); -} - void set_huge_pte_at(struct mm_struct *mm, unsigned long addr, pte_t *ptep, pte_t pte, unsigned long sz) { @@ -257,13 +250,10 @@ void set_huge_pte_at(struct mm_struct *m unsigned long pfn, dpfn; pgprot_t hugeprot;

- if (!pte_present(pte)) { - struct folio *folio; - - folio = hugetlb_swap_entry_to_folio(pte_to_swp_entry(pte)); - ncontig = num_contig_ptes(folio_size(folio), &pgsize); + ncontig = num_contig_ptes(sz, &pgsize);

- for (i = 0; i < ncontig; i++, ptep++) + if (!pte_present(pte)) { + for (i = 0; i < ncontig; i++, ptep++, addr += pgsize) set_pte_at(mm, addr, ptep, pte); return; } @@ -273,7 +263,6 @@ void set_huge_pte_at(struct mm_struct *m return; }

- ncontig = find_num_contig(mm, addr, ptep, &pgsize); pfn = pte_pfn(pte); dpfn = pgsize >> PAGE_SHIFT; hugeprot = pte_pgprot(pte); _

Patches currently in -mm which might be from ryan.roberts@arm.com are

mm-hugetlb-add-huge-page-size-param-to-set_huge_pte_at.patch arm64-hugetlb-fix-set_huge_pte_at-to-work-with-all-swap-entries.patch