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GET /api/patches/2216645/?format=api
{ "id": 2216645, "url": "http://patchwork.ozlabs.org/api/patches/2216645/?format=api", "web_url": "http://patchwork.ozlabs.org/project/linuxppc-dev/patch/20260327021403.214713-13-usama.arif@linux.dev/", "project": { "id": 2, "url": "http://patchwork.ozlabs.org/api/projects/2/?format=api", "name": "Linux PPC development", "link_name": "linuxppc-dev", "list_id": "linuxppc-dev.lists.ozlabs.org", "list_email": "linuxppc-dev@lists.ozlabs.org", "web_url": "https://github.com/linuxppc/wiki/wiki", "scm_url": "https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git", "webscm_url": "https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git/", "list_archive_url": "https://lore.kernel.org/linuxppc-dev/", "list_archive_url_format": "https://lore.kernel.org/linuxppc-dev/{}/", "commit_url_format": "https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git/commit/?id={}" }, "msgid": "<20260327021403.214713-13-usama.arif@linux.dev>", "list_archive_url": "https://lore.kernel.org/linuxppc-dev/20260327021403.214713-13-usama.arif@linux.dev/", "date": "2026-03-27T02:08:54", "name": "[v3,12/24] mm: thp: handle split failure in device migration", "commit_ref": null, "pull_url": null, "state": "handled-elsewhere", "archived": false, "hash": "767e6b38e2482e98c2e1cfadcebffc11527e0610", "submitter": { "id": 92719, "url": "http://patchwork.ozlabs.org/api/people/92719/?format=api", "name": "Usama Arif", "email": "usama.arif@linux.dev" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/linuxppc-dev/patch/20260327021403.214713-13-usama.arif@linux.dev/mbox/", "series": [ { "id": 497678, "url": "http://patchwork.ozlabs.org/api/series/497678/?format=api", "web_url": "http://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=497678", "date": "2026-03-27T02:08:43", "name": "[v3,01/24] mm: thp: make split_huge_pmd functions return int for error propagation", "version": 3, "mbox": "http://patchwork.ozlabs.org/series/497678/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/2216645/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2216645/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "\n <linuxppc-dev+bounces-18855-incoming=patchwork.ozlabs.org@lists.ozlabs.org>", "X-Original-To": [ "incoming@patchwork.ozlabs.org", "linuxppc-dev@lists.ozlabs.org" ], "Delivered-To": "patchwork-incoming@legolas.ozlabs.org", "Authentication-Results": [ "legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256\n header.s=key1 header.b=eUmbqBO7;\n\tdkim-atps=neutral", "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=lists.ozlabs.org\n (client-ip=112.213.38.117; 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a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1;\n\tt=1774577728;\n\th=from:from:reply-to:subject:subject:date:date:message-id:message-id:\n\t to:to:cc:cc:mime-version:mime-version:\n\t content-transfer-encoding:content-transfer-encoding:\n\t in-reply-to:in-reply-to:references:references;\n\tbh=WTevK4s9bqcsyF5dGhWo4MENNp9vZlr+uy9xAQG2jfo=;\n\tb=eUmbqBO72zX2904RPuTC7NJzAIMHlr5gcD4RVYygo1GU1dDyzany1Q2T9JuiXvkcB8DQd9\n\taunpkimHYmudKZq6kRshELjRaFFsIkn5wCDv9o4AVpLZf/bmSb/rct1ebqgCoY+qovcSBc\n\tl6ygYvG/M7DXmErg92nyDDfRdBDaJ3A=", "From": "Usama Arif <usama.arif@linux.dev>", "To": "Andrew Morton <akpm@linux-foundation.org>,\n\tdavid@kernel.org,\n\tLorenzo Stoakes <ljs@kernel.org>,\n\twilly@infradead.org,\n\tlinux-mm@kvack.org", "Cc": "fvdl@google.com,\n\thannes@cmpxchg.org,\n\triel@surriel.com,\n\tshakeel.butt@linux.dev,\n\tkas@kernel.org,\n\tbaohua@kernel.org,\n\tdev.jain@arm.com,\n\tbaolin.wang@linux.alibaba.com,\n\tnpache@redhat.com,\n\tLiam.Howlett@oracle.com,\n\tryan.roberts@arm.com,\n\tVlastimil Babka <vbabka@kernel.org>,\n\tlance.yang@linux.dev,\n\tlinux-kernel@vger.kernel.org,\n\tkernel-team@meta.com,\n\tmaddy@linux.ibm.com,\n\tmpe@ellerman.id.au,\n\tlinuxppc-dev@lists.ozlabs.org,\n\thca@linux.ibm.com,\n\tgor@linux.ibm.com,\n\tagordeev@linux.ibm.com,\n\tborntraeger@linux.ibm.com,\n\tsvens@linux.ibm.com,\n\tlinux-s390@vger.kernel.org,\n\tUsama Arif <usama.arif@linux.dev>", "Subject": "[v3 12/24] mm: thp: handle split failure in device migration", "Date": "Thu, 26 Mar 2026 19:08:54 -0700", "Message-ID": "<20260327021403.214713-13-usama.arif@linux.dev>", "In-Reply-To": "<20260327021403.214713-1-usama.arif@linux.dev>", "References": "<20260327021403.214713-1-usama.arif@linux.dev>", "X-Mailing-List": "linuxppc-dev@lists.ozlabs.org", "List-Id": "<linuxppc-dev.lists.ozlabs.org>", "List-Help": "<mailto:linuxppc-dev+help@lists.ozlabs.org>", "List-Owner": "<mailto:linuxppc-dev+owner@lists.ozlabs.org>", "List-Post": "<mailto:linuxppc-dev@lists.ozlabs.org>", "List-Archive": "<https://lore.kernel.org/linuxppc-dev/>,\n <https://lists.ozlabs.org/pipermail/linuxppc-dev/>", "List-Subscribe": "<mailto:linuxppc-dev+subscribe@lists.ozlabs.org>,\n <mailto:linuxppc-dev+subscribe-digest@lists.ozlabs.org>,\n <mailto:linuxppc-dev+subscribe-nomail@lists.ozlabs.org>", "List-Unsubscribe": "<mailto:linuxppc-dev+unsubscribe@lists.ozlabs.org>", "Precedence": "list", "MIME-Version": "1.0", "Content-Transfer-Encoding": "8bit", "X-Migadu-Flow": "FLOW_OUT", "X-Spam-Status": "No, score=-0.2 required=3.0 tests=DKIM_SIGNED,DKIM_VALID,\n\tDKIM_VALID_AU,DKIM_VALID_EF,SPF_HELO_PASS,SPF_PASS autolearn=disabled\n\tversion=4.0.1 OzLabs 8", "X-Spam-Checker-Version": "SpamAssassin 4.0.1 (2024-03-25) on lists.ozlabs.org" }, "content": "Device memory migration has two call sites that split huge PMDs:\n\nmigrate_vma_split_unmapped_folio():\n Called from migrate_vma_pages() when migrating a PMD-mapped THP to a\n destination that doesn't support compound pages. It splits the PMD\n then splits the folio via folio_split_unmapped().\n\n If the PMD split fails, folio_split_unmapped() would operate on an\n unsplit folio with inconsistent page table state. Propagate -ENOMEM\n to skip this page's migration. This is safe as folio_split_unmapped\n failure would be propagated in a similar way.\n\nmigrate_vma_insert_page():\n Called from migrate_vma_pages() when inserting a page into a VMA\n during migration back from device memory. If a huge zero PMD exists\n at the target address, it must be split before PTE insertion.\n\n If the split fails, the subsequent pte_alloc() and set_pte_at() would\n operate on a PMD slot still occupied by the huge zero entry. Use\n goto abort, consistent with other allocation failures in this function.\n\nSigned-off-by: Usama Arif <usama.arif@linux.dev>\n---\n mm/migrate_device.c | 22 ++++++++++++++++++++--\n 1 file changed, 20 insertions(+), 2 deletions(-)", "diff": "diff --git a/mm/migrate_device.c b/mm/migrate_device.c\nindex 2912eba575d5e..00003fbe803df 100644\n--- a/mm/migrate_device.c\n+++ b/mm/migrate_device.c\n@@ -919,7 +919,19 @@ static int migrate_vma_split_unmapped_folio(struct migrate_vma *migrate,\n \t * drops a reference at the end.\n \t */\n \tfolio_get(folio);\n-\tsplit_huge_pmd_address(migrate->vma, addr, true);\n+\t/*\n+\t * If PMD split fails, folio_split_unmapped would operate on an\n+\t * unsplit folio with inconsistent page table state.\n+\t */\n+\tret = split_huge_pmd_address(migrate->vma, addr, true);\n+\tif (ret) {\n+\t\t/*\n+\t\t * folio_get above was not consumed by split_huge_pmd_address.\n+\t\t * put back that reference.\n+\t\t */\n+\t\tfolio_put(folio);\n+\t\treturn ret;\n+\t}\n \tret = folio_split_unmapped(folio, 0);\n \tif (ret)\n \t\treturn ret;\n@@ -1015,7 +1027,13 @@ static void migrate_vma_insert_page(struct migrate_vma *migrate,\n \t\tif (pmd_trans_huge(*pmdp)) {\n \t\t\tif (!is_huge_zero_pmd(*pmdp))\n \t\t\t\tgoto abort;\n-\t\t\tsplit_huge_pmd(vma, pmdp, addr);\n+\t\t\t/*\n+\t\t\t * If split fails, the huge zero PMD remains and\n+\t\t\t * pte_alloc/PTE insertion that follows would be\n+\t\t\t * incorrect.\n+\t\t\t */\n+\t\t\tif (split_huge_pmd(vma, pmdp, addr))\n+\t\t\t\tgoto abort;\n \t\t} else if (pmd_leaf(*pmdp))\n \t\t\tgoto abort;\n \t}\n", "prefixes": [ "v3", "12/24" ] }