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Howlett , ryan.roberts@arm.com, Vlastimil Babka , lance.yang@linux.dev, linux-kernel@vger.kernel.org, nphamcs@gmail.com, shikemeng@huaweicloud.com, yosry@kernel.org, qi.zheng@linux.dev, luizcap@redhat.com, kernel-team@meta.com, Usama Arif Subject: [PATCH v8 11/30] mm: split PMD swap entries into PTE swap entries Date: Fri, 2 Oct 2026 02:52:25 -0700 Message-ID: <20261002095503.3585565-12-usama.arif@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261002095503.3585565-1-usama.arif@linux.dev> References: <20261002095503.3585565-1-usama.arif@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam06 X-Stat-Signature: 679gm9fn9qyw8gj6nhasm7hsms5cfd8i X-Rspam-User: X-Rspamd-Queue-Id: 0BD9F20006 X-HE-Tag: 1790934989-858010 X-HE-Meta: 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 cL0zKZL4 RB7nYcX+N31hv41DZtmQ+UcrLfXewOSNPJPCDv0J56E5GMzedow6o0+5zITuGiFMszwfgYmczjyNfU/g5kMijUGcE2dqradgq7+560Hak/9GVqUglokVdgQuh1yiENcxc6Gx7w5IaoNeoTvzfA/00PyYePnbcQ8nMxsDjcX7UqAlTKkMoFZvcE69qeYyBjs9vSmsdTK/qMlCOejJ58cePHL2ld246qJKaAMR2 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Once a PMD can hold a swap entry, everything that splits a PMD - mprotect() or munmap() over part of the range, MADV_FREE, a pagewalk with no PMD handler - has to be able to split that entry too. A swap PMD already passes the pmd_is_valid_softleaf() gate, so without this it reaches __split_huge_pmd_locked() and falls through to the present-PMD path, which pmdp_invalidate()s it and calls pmd_page() on a non-present entry. No reference counting is needed: a swap entry pins no folio, and swap_map is already one per slot, so the PTEs simply take over what the PMD held. The migration-only entry point cannot reach the new branch: page_vma_mapped_walk() never hands back a swap PMD, and __split_huge_pmd_locked() already asserts that to_migration_entries implies a present or device-private PMD. Test the pre-split old_pmd rather than re-reading *pmd in the trailing folio_remove_rmap_pmd() gate, so every entry-type test in the function interrogates the same snapshot. That part is cosmetic: pmdp_invalidate() leaves the PMD present as far as software is concerned. Signed-off-by: Usama Arif --- mm/huge_memory.c | 22 +++++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 1df4f619620b4..24d116ae1fc30 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3306,6 +3306,11 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, folio_add_anon_rmap_ptes(folio, page, HPAGE_PMD_NR, vma, haddr, rmap_flags); } + } else if (pmd_is_swap_entry(*pmd)) { + old_pmd = *pmd; + soft_dirty = pmd_swp_soft_dirty(old_pmd); + uffd_wp = pmd_swp_uffd(old_pmd); + anon_exclusive = pmd_swp_exclusive(old_pmd); } else { /* * Up to this point the pmd is present and huge and userland has @@ -3443,6 +3448,21 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, VM_WARN_ON(!pte_none(ptep_get(pte + i))); set_pte_at(mm, addr, pte + i, entry); } + } else if (pmd_is_swap_entry(old_pmd)) { + pte_t entry = softleaf_to_pte(softleaf_from_pmd(old_pmd)); + + if (soft_dirty) + entry = pte_swp_mksoft_dirty(entry); + if (uffd_wp) + entry = pte_swp_mkuffd(entry); + if (anon_exclusive) + entry = pte_swp_mkexclusive(entry); + + for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) { + VM_WARN_ON(!pte_none(ptep_get(pte + i))); + set_pte_at(mm, addr, pte + i, entry); + entry = pte_next_swp_offset(entry); + } } else { pte_t entry; @@ -3470,7 +3490,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, } pte_unmap(pte); - if (!pmd_is_migration_entry(*pmd)) + if (!pmd_is_migration_entry(old_pmd) && !pmd_is_swap_entry(old_pmd)) folio_remove_rmap_pmd(folio, page, vma); if (to_migration_entries) put_page(page); -- 2.53.0-Meta