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 3D9D9263C8F; Tue, 11 Aug 2026 17:07:52 +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=1786468073; cv=none; b=oovXSpBGeV9iGwts+iOrrF/Vz/vI8MUN9DBVoHRPlx8+5pqlFIGgotPRJREiIUU0w2ZJ3rCsSA3QgHO//THssnJyDY/m1N85e9uOWdUKsT1kApmp7bR3+BlqQ8Yw4iDGiDJLgSpp9MGjW7QpOfqQ31qDa59TmlokLQ0hqw40HEk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786468073; c=relaxed/simple; bh=N+mXIOIWXA0/orzNzNwGG39tuU2ATGudf/Z8m3WST2M=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=enfbRKignxBQMv6FDdxJRyH+MKYKfCcYtfjCC5C5MGZ0kyFmzzmzsPvIBtoFZS/wxJm5aGgrKAuedFd/LfKBYsEphhgnPigwVWqYgN9ysanbjWmohdr2vZBS8RAh2f6JZvkOOh0X65DsM8ZL1sPQ0Bv5Ksu6i8sALcVrt0t6MPw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=muZHQpJO; 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="muZHQpJO" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 33E4A1F00A3A; Tue, 11 Aug 2026 17:07:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786468071; bh=iUKLaNVgnm6yVlIUuq3S+v3XbNNRA5IFdKQLUZEf4Po=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=muZHQpJO9uzZAk0kMRcdaEMI9jcfs4Uu8oC32MtScjPY0WQhPC9xcG9YtLeaqYkRQ BghULgIcL5/Ouo5WcMWjVgCzG81bXQD6IdhgzJ6RLsQSkBK03Zm7Q/fe1OeV3TUm0h 46THJIkIrI54+SDkzKF9E0cwdr8sdNPbtzdgd4zMW4gmlKrbgcMHPDNsbQ5FIgOYzV 5i4BQIab45nRpWJ+5/jy2TB8m8BQIVBiwTgWhiKCPfXFIL663Lp+qsXIZ1AuT7UVS6 vdbOBvZg6oEOgAzKgxsuG5rlZ/X3CLkTg0FKOgfOxRCP92SoTKocLw6YIaqodz+n1H r9H212Mfzjw/w== Date: Tue, 11 Aug 2026 18:07:36 +0100 From: "Lorenzo Stoakes (ARM)" To: "David Hildenbrand (Arm)" Cc: Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , "Matthew Wilcox (Oracle)" , Jan Kara , Miaohe Lin , Naoya Horiguchi , Rik van Riel , Harry Yoo , Lance Yang , Kees Cook , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Usama Arif , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Peter Xu , Xu Xin , Chengming Zhou , Arnd Bergmann , Greg Kroah-Hartman , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Sven Schnelle , Alex Deucher , Christian =?utf-8?B?S8O2bmln?= , David Airlie , Simona Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Boris Brezillon , Steven Price , Liviu Dudau , Huang Rui , Matthew Auld , Thomas =?utf-8?Q?Hellstr=C3=B6m?= , Rodrigo Vivi , Masami Hiramatsu , Oleg Nesterov , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , James Clark , Jason Gunthorpe , John Hubbard , Muchun Song , Oscar Salvador , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , Youngjun Park , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, kvm@vger.kernel.org, linux-s390@vger.kernel.org, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, intel-xe@lists.freedesktop.org, linux-perf-users@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH v4 16/20] tools/testing/selftests/mm: test anonymous page offset merge behaviour Message-ID: References: <20260806-b4-scalable-cow-virt-pgoff-v4-0-ab318a350404@kernel.org> <20260806-b4-scalable-cow-virt-pgoff-v4-16-ab318a350404@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Aug 11, 2026 at 06:56:18PM +0200, David Hildenbrand (Arm) wrote: > On 8/6/26 22:21, Lorenzo Stoakes (ARM) wrote: > > While maintaining anonymous page offsets for VMAs has no impact for most > > merge cases, it does impact MAP_PRIVATE-mapped file-backed mappings which > > happen to have matching page offset but not matching anonymous page offset. > > > > Assert this behaviour by attempting to map an unfaulted MAP_PRIVATE-memfd > > region with a faulted one with compatible file page offsets but > > incompatible anonymous page offsets. > > > > Signed-off-by: Lorenzo Stoakes (ARM) > > --- > > tools/testing/selftests/mm/merge.c | 57 ++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 57 insertions(+) > > > > diff --git a/tools/testing/selftests/mm/merge.c b/tools/testing/selftests/mm/merge.c > > index 519e5ac02db7..cb7cdb6b7ada 100644 > > --- a/tools/testing/selftests/mm/merge.c > > +++ b/tools/testing/selftests/mm/merge.c > > @@ -1305,6 +1305,63 @@ TEST_F(merge, merge_vmas_with_mseal) > > ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 2 * page_size); > > } > > > > +TEST_F(merge, anon_and_page_offset_mismatch_memfd) > > +{ > > + struct procmap_fd *procmap = &self->procmap; > > + unsigned int page_size = self->page_size; > > + char *carveout = self->carveout; > > + char *ptr, *ptr2; > > + int fd; > > + > > + /* Create a 10 page memfd descriptor. */ > > + fd = memfd_create("anon_page_offset_test", MFD_CLOEXEC); > > + ASSERT_NE(fd, -1); > > + ASSERT_EQ(ftruncate(fd, 10 * page_size), 0); > > + > > + /* Map a region using the memfd at page offset 0. */ > > + ptr = mmap(carveout, 5 * page_size, PROT_READ | PROT_WRITE, > > + MAP_FIXED | MAP_PRIVATE, fd, 0); > > + ASSERT_NE(ptr, MAP_FAILED); > > + > > + /* > > + * Map another separately, and fault in, at page offset 5: > > + * > > "Fault in" is imprecise, as a read-fault won't do. "Trigger a CoW fault." might > be better. Andrew - could you fix up? Thanks :) > > > Acked-by: David Hildenbrand (Arm) Thanks! > > -- > Cheers, > > David -- Cheers, Lorenzo