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 DD41FC88E45 for ; Fri, 11 Sep 2026 14:18:14 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id F06CF6B0096; Fri, 11 Sep 2026 10:18:13 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id EB6FB6B0098; Fri, 11 Sep 2026 10:18:13 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DBE8A6B0099; Fri, 11 Sep 2026 10:18:13 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id B7DF56B0096 for ; Fri, 11 Sep 2026 10:18:13 -0400 (EDT) Received: from smtpin30.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 52BC9C027E for ; Fri, 11 Sep 2026 14:18:13 +0000 (UTC) X-FDA: 85201686066.30.A77B0A0 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf05.hostedemail.com (Postfix) with ESMTP id 6013110000B for ; Fri, 11 Sep 2026 14:18:11 +0000 (UTC) Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=arm.com header.s=foss header.b=Bbhpiekw; spf=pass (imf05.hostedemail.com: domain of yeoreum.yun@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=yeoreum.yun@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1789136291; b=7kQ0RJyDltwLsq1I8ptpB3OI/FyQyOWQOzV/tvEkK0LiKGjG1kpcK+wKg8x9IWNlcrkhyn Uy3YZdYcKQd6w2nR3wXBDW0IG4+uOgmBRBSAbrxy7yAOLW3EcitNvDrO8cEoYknV9t17VT l+HRZtrhj1jh4XpNufE0kEwkycWM2KE= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=pass header.d=arm.com header.s=foss header.b=Bbhpiekw; spf=pass (imf05.hostedemail.com: domain of yeoreum.yun@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=yeoreum.yun@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1789136291; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=vREt7n9/z/hh4PnMDFuOngpAV7chC/QT0Zx7hnnFb2Y=; b=LUBruQ6arBxNhlMoO4OBB7jnz4A+3L0nkNGHFYJrV7+SCQyMXx9k+n1gjmx8GTXRoaJWqX L1PnY/u6SSdY0dTGtbaQp8HkT1+D/T3jx3vvYz4jLWa3u6g6C0b7of5GGfW3UubINaSPLC xtUzVLdPuP14l5SlhiukSNc3ogMlJI4= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 9AD9316A3; Fri, 11 Sep 2026 07:18:06 -0700 (PDT) Received: from e129823.arm.com (unknown [10.2.213.3]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 535DE3F7B4; Fri, 11 Sep 2026 07:18:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1789136290; bh=SMWTVWYkHCdUnE1Ea2H43xOdc3TkjyJelBC5ssmIAow=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Bbhpiekw4vPtMuSsZQAsZFKlWtlBiNZqWOGJYa2TIZ7tf2EDzfoA4yJdja9s9TwSC aqPhmIMiLGxUG3I8yFttZOXdPfb5XYZmn5G0AD0U1IgwHhCMWc2scpQNxBeJ9pr5g/ t3+tyW6g4se59IaKlJahdDLa4IbzqgPavRxnjBxA= Date: Fri, 11 Sep 2026 15:18:05 +0100 From: Yeoreum Yun To: "Lorenzo Stoakes (ARM)" Cc: Yeoreum Yun , linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, david@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com Subject: Re: [PATCH] kselftest: mm: fix potential failure for merged VMA in guard-regions Message-ID: References: <20260911123534.1181501-1-yeoreum.yun@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 6013110000B X-Rspam-User: X-Stat-Signature: qmpbocdqxurmyxyopk97hbidwnmiarkc X-HE-Tag: 1789136291-608801 X-HE-Meta: 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 cInRzrbh t1jOWIiTfd7OMuMLf4r2iwaNQEoAZnkuoN74NI4JdFsVjfQBYHGsmiLQtBkPX5EueRD/8H6tUuXCtjtRVrefC/Rzm9bRiGFA3srRlV/pczk4uvUrYwJhHKFATZSGtvcaeA1Nnwm/1lsVJ3Pu8IltuzkbyeH+/Gl5EU2+9o4YG7zdVzoiqk+DDsUA+o1N9Ct0y8vgrpJ/TQ5De8z9XuVGmHFrIYt4zHR6PDvO2aW9C6QE/nvtkYJ8RnfmGCz/ZpxKFO4Rv+NJV7mdXAuAcJk38yIsAdT8hCndk+00NdkLPTFBHr5k= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > On Fri, Sep 11, 2026 at 02:51:09PM +0100, Lorenzo Stoakes (ARM) wrote: > > On Fri, Sep 11, 2026 at 02:34:37PM +0100, Yeoreum Yun wrote: > > > On Fri, Sep 11, 2026 at 01:59:31PM +0100, Lorenzo Stoakes (ARM) wrote: > > > > On Fri, Sep 11, 2026 at 01:35:34PM +0100, Yeoreum Yun wrote: > > > > > check_vmflag_guard() uses /proc/self/smaps to retrieve the VMA flags, > > > > > but this can fail if the mapping is merged with an adjacent VMA. > > > > > > > > > > To avoid this potential failure, first allocate a temporary region with > > > > > extra pages at both ends, unmap it, and then map the test region within > > > > > the temporary address range, leaving an unmapped page on each side to > > > > > prevent VMA merging. > > > > > > > > > > Signed-off-by: Yeoreum Yun > > > > > --- > > > > > tools/testing/selftests/mm/guard-regions.c | 14 ++++++++++++-- > > > > > 1 file changed, 12 insertions(+), 2 deletions(-) > > > > > > > > > > diff --git a/tools/testing/selftests/mm/guard-regions.c b/tools/testing/selftests/mm/guard-regions.c > > > > > index 5c8ec3ca75d7..a28a57d34e97 100644 > > > > > --- a/tools/testing/selftests/mm/guard-regions.c > > > > > +++ b/tools/testing/selftests/mm/guard-regions.c > > > > > @@ -2257,8 +2257,18 @@ TEST_F(guard_regions, smaps) > > > > > char *ptr, *ptr2; > > > > > int i; > > > > > > > > > > - /* Map a region. */ > > > > > - ptr = mmap_(self, variant, NULL, 10 * page_size, PROT_READ | PROT_WRITE, 0, 0); > > > > > + /* Try to Map a region. */ > > > > > > > > Map -> map > > > > > > > > > + ptr = mmap_(self, variant, NULL, 12 * page_size, PROT_READ | PROT_WRITE, 0, 0); > > > > > > > > Should be PROT_NONE otherwise it'll merge with the below. > > > > > > It doesn't matter. since this memory is unmapped and then second map > > > at ptr + page_size. > > > > > > IOW, though the first one is merged, it unammped and then > > > the second is allocated at ptr + page_size, it wouldn't be merged: > > > > > > after unmap: > > > [existing VMA][ 12 pages ][existing VMA] > > > > > > second: > > > [exiting VMA] [hole (page)] [ 10 pages (for test)] [hole (page)] [existing VMA] > > > > > > Am I missing something? > > > > Yeah, unmapped (unfaulted) VMAs can be merged with mapped (faulted) VMAs. > > > > In general it's also better to be explicit by specifying distinct attributes > > anyway to spell out clearly that the VMAs are intended to perform that task. > > Oops, I missed that you immediately unmapped the VMA too :) > > In that case it's fine but I'd still prefer it PROT_NONE to clearly single it > out as a placeholder. > > Also a comment above it like: > > /* Map then unmap placeholder to avoid adjacent merges */ Might the ASSERT() made you miss the unmap :). I'll post soon again. Thanks! -- Sincerely, Yeoreum Yun