From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id EA155CEACEF for ; Mon, 17 Nov 2025 15:12:00 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3E6318E0016; Mon, 17 Nov 2025 10:12:00 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 396388E0002; Mon, 17 Nov 2025 10:12:00 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 285668E0016; Mon, 17 Nov 2025 10:12:00 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 110DF8E0002 for ; Mon, 17 Nov 2025 10:12:00 -0500 (EST) Received: from smtpin05.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 7FB87160141 for ; Mon, 17 Nov 2025 15:11:59 +0000 (UTC) X-FDA: 84120439158.05.9392FD7 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf30.hostedemail.com (Postfix) with ESMTP id A749780012 for ; Mon, 17 Nov 2025 15:11:57 +0000 (UTC) Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=fYFQfp98; spf=pass (imf30.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1763392317; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=2+XeOac7x9dGcuLMSUxMnESiDOWeN3Lx2j0ugWvLhI0=; b=aZcT5YYMoBNogBfqP806d+yz3HJJ12IxAQan7U55bk3I/2I4pLyrdbLKYfWO5Yhx1r+odk eNH9ibE1jwmrSTtEyfzIYmwR6SjvFnL+khi1TswFeRGdG053odpa7MxAWHycgFw5cUTJuk aIl0IC5A6/BSkxsI//HANACbQWkxfZI= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=fYFQfp98; spf=pass (imf30.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1763392317; a=rsa-sha256; cv=none; b=bltMxS8E4+wRfADwaAeyVxZDnTQOzu6QDCY4ZEZXKZezqs+aGXKwsOrDWWq9hhd415oMTv 1gG1pNvD4OTQ/qI+aqoFy3aZV3JshfFLVCz+iaXZDR8bCPCkaG3KzQkSy63Nm7yDwLeoGM BHO2CUwE6DBtPWLhXKTeQwL0Nz8Vyk0= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 43AB2444F9; Mon, 17 Nov 2025 15:11:56 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9D213C113D0; Mon, 17 Nov 2025 15:11:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1763392316; bh=TwfGBepi2IUAU/4JFAvHJYTM1sRw3y0VTMA2H2PFuPQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=fYFQfp98q8CZPq2D3/1HwhNKfQ02GOU/p/lXsiGElTjPUzEmC11RUcdhfE0uh+LZe hkTadqxNsT86x26pV78yE9cHtXOZohKJc0CnrhNLYiIZQceAFHoqFiPE78DidXhXLN tFAKq7VHPXZt3xIHdv8rlwuvCmnXJCirwhXCPCvCDSY+GaHO9QVUWndBeMs4LtVKhB vXQzJeyLQ5i7XRjJafFG+RpCQs24WSu+XrfAhKl64rdC/PRf63+PQQaFX6cPXenQKt k5jwAq/pMGJUEEMPjo9TEaBxkVgMEBH/vcGjv4clAdluHxZE2X66gZlaSyNyJg/OV1 zEIIjPZilJmXA== Message-ID: <9e617d7b-afd7-465b-b075-32b02257b90b@kernel.org> Date: Mon, 17 Nov 2025 16:11:47 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/8] mm: introduce VM_MAYBE_GUARD and make visible in /proc/$pid/smaps To: Lorenzo Stoakes , Andrew Morton Cc: Jonathan Corbet , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Jann Horn , Pedro Falcato , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Andrei Vagin References: <94d1e9c6c6dd8a4de1f2a8022ca92e2e320730ff.1762531708.git.lorenzo.stoakes@oracle.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: <94d1e9c6c6dd8a4de1f2a8022ca92e2e320730ff.1762531708.git.lorenzo.stoakes@oracle.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: A749780012 X-Stat-Signature: opitk9qkopkat5pcjf1ips83wpnokpbf X-Rspam-User: X-HE-Tag: 1763392317-170895 X-HE-Meta: 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 jT1GCt5K z8OWzN81q1yU4Ar7sVvzyHHPb2OnOjqr3D5JY8ss/yCgWp3uY0SR/8vbbhXVQVNfrrVYNvuFjTj2prtEuKDMOv0MGov2l0+oHhXW90qfjARc9jZsy+VLtNJap8xt0hWzDDttwAwK8JZ8oscCc031rUj2IYovXiDkM6uDYVeho5UQDcbj6zPJAy0WwDFCi2qYsTi8a9eRnXTqrrQJ+COGLttyFt0sG1GWaXbBl9lUBCnorHNNn71jdWxc07P4BiKMmWWyA8bCngrtipHQOJO5hHkEYWiXYbz/BSA/vrVqmcbNyp6ASokxv79kgfkui+EwL3PiWvzM5ITo1V8KaVSUFAV2l3o9622RKmdplUEiFJAcILvoHhQp+oJq+GtIO3+qcaGTLh+85ZtQvlHQ= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 07.11.25 17:11, Lorenzo Stoakes wrote: > Currently, if a user needs to determine if guard regions are present in a > range, they have to scan all VMAs (or have knowledge of which ones might > have guard regions). > > Since commit 8e2f2aeb8b48 ("fs/proc/task_mmu: add guard region bit to > pagemap") and the related commit a516403787e0 ("fs/proc: extend the > PAGEMAP_SCAN ioctl to report guard regions"), users can use either > /proc/$pid/pagemap or the PAGEMAP_SCAN functionality to perform this > operation at a virtual address level. > > This is not ideal, and it gives no visibility at a /proc/$pid/smaps level > that guard regions exist in ranges. > > This patch remedies the situation by establishing a new VMA flag, > VM_MAYBE_GUARD, to indicate that a VMA may contain guard regions (it is > uncertain because we cannot reasonably determine whether a > MADV_GUARD_REMOVE call has removed all of the guard regions in a VMA, and > additionally VMAs may change across merge/split). > > We utilise 0x800 for this flag which makes it available to 32-bit > architectures also, a flag that was previously used by VM_DENYWRITE, which > was removed in commit 8d0920bde5eb ("mm: remove VM_DENYWRITE") and hasn't > bee reused yet. > > We also update the smaps logic and documentation to identify these VMAs. > > Another major use of this functionality is that we can use it to identify > that we ought to copy page tables on fork. > > We do not actually implement usage of this flag in mm/madvise.c yet as we > need to allow some VMA flags to be applied atomically under mmap/VMA read > lock in order to avoid the need to acquire a write lock for this purpose. > > Reviewed-by: Pedro Falcato > Reviewed-by: Vlastimil Babka > Signed-off-by: Lorenzo Stoakes > --- > Documentation/filesystems/proc.rst | 5 +++-- > fs/proc/task_mmu.c | 1 + > include/linux/mm.h | 3 +++ > include/trace/events/mmflags.h | 1 + > mm/memory.c | 4 ++++ > tools/testing/vma/vma_internal.h | 1 + > 6 files changed, 13 insertions(+), 2 deletions(-) > > diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst > index 0b86a8022fa1..8256e857e2d7 100644 > --- a/Documentation/filesystems/proc.rst > +++ b/Documentation/filesystems/proc.rst > @@ -553,7 +553,7 @@ otherwise. > kernel flags associated with the particular virtual memory area in two letter > encoded manner. The codes are the following: > > - == ======================================= > + == ============================================================= > rd readable > wr writeable > ex executable > @@ -591,7 +591,8 @@ encoded manner. The codes are the following: > sl sealed > lf lock on fault pages > dp always lazily freeable mapping > - == ======================================= > + gu maybe contains guard regions (if not set, definitely doesn't) > + == ============================================================= In general LGTM, BUT in the context of this patch where the flag is never set, that's not entirely correct ;) It made sense after staring at patch #5. Acked-by: David Hildenbrand (Red Hat) -- Cheers David