From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-41.mta0.migadu.com [91.218.175.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EECFE45C71C for ; Mon, 14 Sep 2026 12:31:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.41 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789389097; cv=none; b=POZprCsTT/EKAiNSPPp5A0FfiHAvaJzQQB3PY3ts21ZSjlx1HxDxBsQTVAM0w9bU2wc6QXEJcTui9c8tcE40HRmkIhkT3WM3YibSVJRwI1S7IKzL57gw+NJcri0FK5z9+OnXUG5a8OPd5dKfUvU3dsDSbYEjYR5ng1V+rmwID7E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789389097; c=relaxed/simple; bh=Q7Vo+oMZWSnoi9kpct14wrtvWt95QszpUVVNkFyr/6c=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=IKYbpV87KPAX0huE5VDBc38V/ozFi3htz95/d3h5utonimi64eUocV7YHoOcXSSkAuAmx6TXb8C/7FywGvxBUSCE/K8nW8LpIdyc3Aup1sAWsEnW99wvB8mXE5yyUaol1nWTMxjhn91t/gqu+Eu2vFyPsDB3uUUUU40QFX6z3nc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=Z5GhJrBL; arc=none smtp.client-ip=91.218.175.41 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="Z5GhJrBL" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=Q7Vo+oMZWSnoi9kpct14wrtvWt95QszpUVVNkFyr/6c=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1789389086; v=1; x=1789993886; b=Z5GhJrBLiU2mFJd2D90uchgd529Y/fai1OvFUV9kqOBTIdFvKQ0Q6ePS/l9kPiszDgm6pNsb 8DvDCL7/SaRToSr+wmIf4qNysI19355EWN4HBhqZiJyPz/YplWoUDECQmwCxOWMporw7/UMe3cI d/6uRIU5A+MsstqisGYQ1IjY= X-Envelope-To: linux-kernel@vger.kernel.org Received: by mta11.migadu.com with ESMTPS id 56156af8bd9f1fa3; Mon, 14 Sep 2026 12:31:26 +0000 X-Mizu-Trace-ID: 56156af8bd9f1fa3 X-Migadu-Flow: FLOW_OUT From: Usama Arif To: Andrew Morton , david@kernel.org, chrisl@kernel.org, kasong@tencent.com, ljs@kernel.org, ziy@nvidia.com, linux-mm@kvack.org Cc: ying.huang@linux.alibaba.com, Baoquan He , willy@infradead.org, youngjun.park@lge.com, hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev, alex@ghiti.fr, kas@kernel.org, baohua@kernel.org, dev.jain@arm.com, baolin.wang@linux.alibaba.com, Nico Pache , Liam R. 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: [RESEND v7 11/29] mm: split PMD swap entries into PTE swap entries Date: Mon, 14 Sep 2026 05:28:01 -0700 Message-ID: <20260914122950.3283997-12-usama.arif@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260914122950.3283997-1-usama.arif@linux.dev> References: <20260914122950.3283997-1-usama.arif@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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, or the callers that rely on split_huge_pmd() to hand them a PTE table would find the PMD unchanged. 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, because page_vma_mapped_walk() never hands back a swap PMD for the folio being migrated. Warn if that ever changes, and force the regular split anyway, since the branch leaves folio and page uninitialised. 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 | 36 +++++++++++++++++++++++++++++++++++- 1 file changed, 35 insertions(+), 1 deletion(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 873887aed0bc2..0e347a545588c 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3304,6 +3304,21 @@ 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)) { + /* + * A PMD swap entry has no page, so it cannot be turned into + * PTE migration entries. page_vma_mapped_walk() never hands + * one back for the folio being migrated, so this should not + * happen; warn, but also force the regular split so that a + * broken invariant cannot make the code below dereference the + * uninitialised folio and page. + */ + VM_WARN_ON_ONCE(use_migration_entries); + use_migration_entries = false; + 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 @@ -3440,6 +3455,25 @@ 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)) { + const softleaf_t old_entry = softleaf_from_pmd(old_pmd); + pte_t pte_swp_entry; + swp_entry_t entry; + + for (i = 0, addr = haddr; i < HPAGE_PMD_NR; + i++, addr += PAGE_SIZE) { + entry = swp_entry(swp_type(old_entry), + swp_offset(old_entry) + i); + pte_swp_entry = swp_entry_to_pte(entry); + if (soft_dirty) + pte_swp_entry = pte_swp_mksoft_dirty(pte_swp_entry); + if (uffd_wp) + pte_swp_entry = pte_swp_mkuffd(pte_swp_entry); + if (anon_exclusive) + pte_swp_entry = pte_swp_mkexclusive(pte_swp_entry); + VM_WARN_ON(!pte_none(ptep_get(pte + i))); + set_pte_at(mm, addr, pte + i, pte_swp_entry); + } } else { pte_t entry; @@ -3467,7 +3501,7 @@ 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 (use_migration_entries) put_page(page); -- 2.53.0-Meta