From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CD5EF2BB17 for ; Thu, 18 Jun 2026 07:27:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781767648; cv=none; b=N9MFJlqqvfULW2idF4NVOByR4rZgCiQU5maz1n7nP5ovZYLcJBLx7XrAaiYqkC2pQorQ0FtmEiaaVhe77SwBZlNYdroqFINIZ/EhJSB3qw2EWp3b5/69n/qq68wPDIxQ+HeSKkFuPdkZLgda9931rhI09hx4DNgSKPM9+dkyjeA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781767648; c=relaxed/simple; bh=7SYxaYYf0ly+UFBJDZmW9b63mCnWSQiyLe8NWCOgPP4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=U1+9oP5uCQs5gvFqrnDARBj0rig4hJkf5FxVVjT0T+dCcEiAiWddPW27FqhJjdiNfvtpwzDnI5Uqzlcj9Ke5w8p/15aZZMJjEhbuqGbQFBHW1AtwDOMqkcV8ANYkE6Z+QDfx6SASBbPcJwtA6j0GMGr749lvX07+6mFP7cT6hGw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=jEvfewlg; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="jEvfewlg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BA78E1F000E9; Thu, 18 Jun 2026 07:27:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781767647; bh=DMRA1kS0c5QJW6KjK0w1R4M6xusuj/MFHWPIs+KMaDo=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=jEvfewlgsozJDyY9uc5/XwOP7JZxkV+lvPJOs51kM7dUP0KQWyaXfliYM4UzWctJS UbLc2DJIqHpeSxSySfXC0MS5lz6iBqZAM4vGS/Irvll/kpYC9rKcoOb+rP2QdUgufU PC8bOBpmXkTZBkTt568/S6rZIibIWPRXvH5N93PLsnAjcI2SnsE5jzRCwA6yism1rL 2Hu/nUPlASLTfQVJSCYZfBew6+8Fr3lMiw3mu/d0/ZjEKWzrobYue515OGF7XvdnSA q+NewhUkPs5UFIK37p8e4IIMAsZvp8wjwbucGi9/2gOZjmywM32POsXyf+F9XzKxaD eTkReyk0n6wXA== Message-ID: <7b2125bb-c2d6-4678-9ae3-6f4e93034391@kernel.org> Date: Thu, 18 Jun 2026 09:27:24 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 0/4] mm/page_owner: add per-fd filter infrastructure for print_mode and NUMA filtering Content-Language: en-US To: "zhen.ni" , Andrew Morton Cc: surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260525081652.2210206-1-zhen.ni@easystack.cn> <20260525125819.1857f215bc56b26a0727bedc@linux-foundation.org> <5ef656db-c6b6-4a2c-b6be-628e5214952f@easystack.cn> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 6/17/26 10:52, zhen.ni wrote: > 在 2026/5/26 03:58, Andrew Morton 写道: >> On Mon, 25 May 2026 16:16:48 +0800 Zhen Ni wrote: >> >>> This patch series introduces per-file-descriptor filtering capabilities to the >>> page_owner feature. >> >> Thanks again. AI review has found a bunch of new things to get worried >> about: >> https://sashiko.dev/#/patchset/20260525081652.2210206-1-zhen.ni@easystack.cn >> >> > Hi, > > Can this lead to an out-of-bounds memory read? > > The NUMA filter in page_owner (mm/page_owner.c:790-798) bypasses > PF_POISONED_CHECK() to avoid triggering VM_BUG_ON during concurrent page > allocation/free: > > int page_nid = memdesc_nid(page->flags); > > When NODE_NOT_IN_PAGE_FLAGS is defined, memdesc_nid() performs unchecked > array access: > > int memdesc_nid(memdesc_flags_t mdf) > { > return section_to_node_table[memdesc_section(mdf)]; > } > > If page->flags is poisoned, memdesc_section() can return a garbage > section_nr that causes out-of-bounds access. > > ## Lockless Access Safety Principle > > The page_owner iterator runs without locks, meaning pages can be > allocated or freed concurrently. The fundamental design principle should be: > > "It's acceptable to skip a small number of abnormal pages, but panics > must be prevented." > > In lockless iteration, TOCTOU is unavoidable - even with reference > counting or RCU, page->flags can still be modified concurrently during > access. Zone locks prevent this but are prohibitively expensive. > > ## Proposed Solution: Add nid to struct page_owner > > Record nid at allocation time when page state is stable, eliminating the > need to extract it from page->flags during iteration: > > ### 1. Modify struct page_owner > > struct page_owner { > unsigned short order; > short last_migrate_reason; > ... > pid_t tgid; > pid_t free_pid; > pid_t free_tgid; > int nid; // NEW > }; > > ### 2. Record nid during allocation > > static inline void __update_page_owner_handle(struct page *page, ...) > { > int nid = page_to_nid(page); // Safe in allocation context > > for_each_page_ext(page, 1 << order, page_ext, iter) { > page_owner = get_page_owner(page_ext); > page_owner->nid = nid; > // ... other fields ... > } > } > > ### 3. Use saved nid in NUMA filter > > if (state->nid_filter_enabled) { > int page_nid = page_owner->nid; // Direct read, safe > > if (!node_isset(page_nid, state->nid_filter)) { > spin_unlock_irqrestore(&state->lock, flags); > goto ext_put_continue; > } > } > > ### 4. Update nid on page migration > > // In split_page_owner() when page migrates > page_owner->nid = page_to_nid(&newfolio->page); > This (presumably LLM) suggestion is a, let's say "lazy" solution to the problem, leading to more memory usage. I'd be surprised if it's not possible to read the nid in a way that avoids the hazards. If page_to_nid() can trigger a VM_BUG_ON(), then I'd add a version without that VM_BUG_ON(), handling the poisoned state gracefully - if it's poisoned, return e.g. NUMA_NO_NODE and skip the page, or something. > The remaining two issues can also be improved. If there are no > additional comments, I will proceed with sending v10. > > > Thanks, > Zhen