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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1772105641; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=3zn8+Git0EggRmhaca5IE2gupO7ol+4qJNppzm+/Ej8=; b=C44MfwaQZXC9xurNJm1Gj33Zxo1gLQS8k4IWyBzLJ3bDH3iEaWw2xI76yUVCOJhu+N0fjz uImfnhnDx1t7VDozyvgsx0dmj2PUnj69wqMG8MPzuScq2zzmXFeTbiFWn+QmycgKIMWYDT hh2GKNuNvA84UQEGRKDJ+AfYcSWycUg= From: Usama Arif To: Andrew Morton , david@kernel.org, lorenzo.stoakes@oracle.com, willy@infradead.org, linux-mm@kvack.org Cc: fvdl@google.com, hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev, kas@kernel.org, baohua@kernel.org, dev.jain@arm.com, baolin.wang@linux.alibaba.com, npache@redhat.com, Liam.Howlett@oracle.com, ryan.roberts@arm.com, Vlastimil Babka , lance.yang@linux.dev, linux-kernel@vger.kernel.org, kernel-team@meta.com, maddy@linux.ibm.com, mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org, hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, borntraeger@linux.ibm.com, svens@linux.ibm.com, linux-s390@vger.kernel.org, Usama Arif Subject: [RFC v2 11/21] mm: thp: handle split failure in userfaultfd move_pages() Date: Thu, 26 Feb 2026 03:23:40 -0800 Message-ID: <20260226113233.3987674-12-usama.arif@linux.dev> In-Reply-To: <20260226113233.3987674-1-usama.arif@linux.dev> References: <20260226113233.3987674-1-usama.arif@linux.dev> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT The UFFDIO_MOVE ioctl's move_pages() loop splits a huge PMD when the folio is pinned and can't be moved at PMD granularity. If the split fails, the PMD stays huge and move_pages_pte() can't process individual pages. Break out of the loop on split failure and return -ENOMEM to the caller. This is similar to how other allocation failures (__pte_alloc, mm_alloc_pmd) are handled in move_pages(). Signed-off-by: Usama Arif --- mm/userfaultfd.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index e19872e518785..2728102e00c72 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -1870,7 +1870,13 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start, } spin_unlock(ptl); - split_huge_pmd(src_vma, src_pmd, src_addr); + /* + * If split fails, the PMD stays huge and + * move_pages_pte can't process it. + */ + err = split_huge_pmd(src_vma, src_pmd, src_addr); + if (err) + break; /* The folio will be split by move_pages_pte() */ continue; } -- 2.47.3