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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1772105610; 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=HcjsQV50nDatk8NFhsm3n/z/wAZY5b80YB+EzBptEz0=; b=hUNYtyZhaqlksnd9AfSZRt096lmVApHmXGQuSN2BpnlEr3x8YHG94GOzMTUoa/3r7gWEkq 45emp28Vxqc7n2wBQVg1LWyfVHtjlcaJ4w3bF7QR+JjA9SJu1LjAHrKEC+xPZYvhAhbt9r GhTu0cvDNKxZfXQZTdIFSvNtBxE363I= 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 05/21] mm: thp: handle split failure in zap_pmd_range() Date: Thu, 26 Feb 2026 03:23:34 -0800 Message-ID: <20260226113233.3987674-6-usama.arif@linux.dev> In-Reply-To: <20260226113233.3987674-1-usama.arif@linux.dev> References: <20260226113233.3987674-1-usama.arif@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 57E19100009 X-Stat-Signature: jysczmdp8f9se3pitfhitny1xmnbmz18 X-HE-Tag: 1772105612-276908 X-HE-Meta: U2FsdGVkX183tv26SxmFyrtp1nJav9vqqL05q3VefFktuU5y2W7qC1ER3rHuKvmvPNFJ/U/rwrgJF7Lwm8DPcqsnXvwcWw1XNyDjOPuqzjfeGFpK4WPRBeImFphWiPORsA8WZyA328w3yn2brGxcK4X5BjHLJ7npVpSi15w61xYtZJu6FSiC/rjTaXzu4OBVYMukus3mEJqlTueSzsh+GIbe/L6JcoeY/UJhzMdFmCA/Nta0MY6bJIs+VpIWl7GKOrzOZmfy8xvtixYdE76vF5aNeticAFPbtUcyDZti5Enc3DHPXSTu/k9huP47tbABv+5OI9BrPoY2BkShRZFL8mLrhZFUdMo2N1jddEEu3R91Ne8ZtTJ/J7SEw9hwicMVTnrovdN+tBqiW20WQMyelWQz3rLObl7/REfLpoyzYJPhKAPd4BMqvYeTAmtHl8tyYotohBwFp/LAmH9uTU7N7x2Xw98mZST7Zdg2F4xFyqLrH/NJW50TmbMvsInCpTvzQq3zmx5UlT9X5sq56uSem7XB/J9MxRNyH/6KgVzyTq587iIujA/7iOcZoOBpZOGUWpPcM8sOOJG7oQUd6MtJDovjJyEDpAZzDH9xFl4moo54EqQocsODXL6RwDkS+0jrkmiKtFu8grJTmWOPbD8VsiOhwTpYPkeoQKlvS099gJKY7Fiyk/0h0V/sqe+AYC/EUFwbgaRmDjAQNd3txZl97il9MVT56IsIBiJpCREiXJfjofqErcfE0jkC0bv5tQhK1GbGV6P+l/lUujkbh4Y7QjLIme3QtER3ntcLyte3x9rN1QOqEvQL/uvrueii15F3vvWSnmKfpuq4HxDMhLnYw+N9bPU0YAgP9cmh4KOROIfD9UcrTnNh19KhLSdxoRPgChzqrYm67u9L0LqkYayi1JKAy6x0WuvTiml+rGB9KtLVvc/VfQKuRbvQjUId/fH43e8BkLns42CmGtVR9vm Z7bmxEu9 tvanGaUfJDLSlbNzMY8ivtJX8Z37BNJuyhUFn3jrPNy0254DDoPC3cZLGfcik4pUeCKYwUkXQU/b1st2ZhP4GrENrOc89LQnC4WUSlKjvPIiSPLmK531L0AQSYMjqMMWnWIJdANXWvxDZ4KAmCC+z0+7WXOQszJc0uzp2AlYQiWaXSl1hAvFsIyZLhnwlDmwLktNRcgV634FPDB82yWS5gXAwwc44Wt9MLrPLfJQA5swGROeMwIaXjhKGG2kAQqw7b6iJ6xheZOwgt7OuyzkQwbncvA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: zap_pmd_range() splits a huge PMD when the zap range doesn't cover the full PMD (partial unmap). If the split fails, the PMD stays huge. Falling through to zap_pte_range() would dereference the huge PMD entry as a PTE page table pointer. Skip the range covered by the PMD on split failure instead. The skip is safe across all call paths into zap_pmd_range(): - exit_mmap() and OOM reaper: the zap range covers entire VMAs, so every PMD is fully covered (next - addr == HPAGE_PMD_SIZE). The zap_huge_pmd() branch handles these without splitting. The split failure path is unreachable. - munmap / mmap overlay: vma_adjust_trans_huge() (called from __split_vma) splits any PMD straddling the VMA boundary before the VMA is split. If that PMD split fails, __split_vma() returns -ENOMEM and the munmap is aborted before reaching zap_pmd_range(). The split failure path is unreachable. - MADV_DONTNEED: advisory hint, the kernel is allowed to ignore it. The pages remain valid and accessible. A subsequent access returns existing data without faulting. Signed-off-by: Usama Arif --- mm/memory.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index 9385842c35034..7ba1221c63792 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1983,9 +1983,18 @@ static inline unsigned long zap_pmd_range(struct mmu_gather *tlb, do { next = pmd_addr_end(addr, end); if (pmd_is_huge(*pmd)) { - if (next - addr != HPAGE_PMD_SIZE) - __split_huge_pmd(vma, pmd, addr, false); - else if (zap_huge_pmd(tlb, vma, pmd, addr)) { + if (next - addr != HPAGE_PMD_SIZE) { + /* + * If split fails, the PMD stays huge. + * Skip the range to avoid falling through + * to zap_pte_range, which would treat the + * huge PMD entry as a page table pointer. + */ + if (__split_huge_pmd(vma, pmd, addr, false)) { + addr = next; + continue; + } + } else if (zap_huge_pmd(tlb, vma, pmd, addr)) { addr = next; continue; } -- 2.47.3