From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx0a-00082601.pphosted.com (mx0a-00082601.pphosted.com [67.231.145.42]) (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 858162D8796; Thu, 18 Sep 2025 19:12:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=67.231.145.42 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758222751; cv=none; b=GxBomJlv0p0R2KiKZWGQ9dhGqwz6GT+wQAJHtc3cnWr3L0yo/eZl8Wj5PQ5nwLC97ABA1O5dVxaxWXnJ0E1ZV19bPgVE4e780VmvmekfvuQrLtthEz3ASusu7LbvZTAs4pEfC/oZ4elTKcG76tw85/1JFqjRS7OO+q6QzU1aeOs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758222751; c=relaxed/simple; bh=lOR27FB60WfaXG9XY9l0rBk9RW2/T7eyBicEZvQ9F+4=; h=From:To:CC:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=SeW5l1FPiy7XmpTFhlCpoJOpL1g4WwIQL5acXVZ8VQHpsonPvY44a9HTlaOqIfU8QHHcQH6DW35lEEYsKRonY6msls2kAX81XgZWDVOdQs3m5qhgtYP+kWrbaSD/204r+QWspgrD8jY0chwb4cZGHdkCPF0k/Mtoh6F9Qg1mb8A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=meta.com; spf=pass smtp.mailfrom=meta.com; dkim=pass (2048-bit key) header.d=meta.com header.i=@meta.com header.b=e1PjzYEw; arc=none smtp.client-ip=67.231.145.42 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=meta.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=meta.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=meta.com header.i=@meta.com header.b="e1PjzYEw" Received: from pps.filterd (m0148461.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 58IHFrYs3277934; Thu, 18 Sep 2025 12:11:42 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=meta.com; h=cc :content-transfer-encoding:content-type:date:from:in-reply-to :message-id:mime-version:references:subject:to; s=s2048-2025-q2; bh=n7WMUyT5L/wA654bmEoUeQzuO+YeNxS6ichaQfAm4K0=; b=e1PjzYEwP6rW SfUk5eeciJxn+YRaNAOwJfo0mF1M9af1ue6fOutyvFad79DSht413xYSjq60mDZn YfAeHI3teHoLHj2Ahw36GPsEKjr9nWC6XNFV5yDHpZFkBziHEg6+zY9tRtbFHZ7L euLc+3yKJdYsaDbCHeYUrokmz4OdnyNONXB/EoFpk84RGhgSRcJayfWUqspezpej t5GboU+18x4kwUz9VDEY546JJy77c6NrIDp7S3nspwxS3VyRR3cDcJUXjns/AlUx vHU6c1NA5Yk/53XX8iJhs34HuxkDG9lTlReCBuQkPbYQPU3FHSiVsk3ft4wTv6TT ArN8tU50uw== Received: from mail.thefacebook.com ([163.114.134.16]) by mx0a-00082601.pphosted.com (PPS) with ESMTPS id 498f7yccgs-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT); Thu, 18 Sep 2025 12:11:41 -0700 (PDT) Received: from devbig091.ldc1.facebook.com (2620:10d:c085:108::150d) by mail.thefacebook.com (2620:10d:c08b:78::c78f) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.2.2562.20; Thu, 18 Sep 2025 19:11:36 +0000 From: Chris Mason To: Lorenzo Stoakes CC: Chris Mason , Andrew Morton , Matthew Wilcox , Guo Ren , "Thomas Bogendoerfer" , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , "David S . Miller" , Andreas Larsson , Arnd Bergmann , Greg Kroah-Hartman , "Dan Williams" , Vishal Verma , Dave Jiang , Nicolas Pitre , "Muchun Song" , Oscar Salvador , "David Hildenbrand" , Konstantin Komarov , Baoquan He , Vivek Goyal , Dave Young , Tony Luck , Reinette Chatre , "Dave Martin" , James Morse , "Alexander Viro" , Christian Brauner , "Jan Kara" , "Liam R . Howlett" , "Vlastimil Babka" , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Hugh Dickins , Baolin Wang , "Uladzislau Rezki" , Dmitry Vyukov , "Andrey Konovalov" , Jann Horn , Pedro Falcato , , , , , , , , , , , , , , Jason Gunthorpe Subject: Re: [PATCH v2 11/16] mm: update mem char driver to use mmap_prepare Date: Thu, 18 Sep 2025 12:11:05 -0700 Message-ID: <20250918191119.3622358-1-clm@meta.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: References: Precedence: bulk X-Mailing-List: ntfs3@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-Authority-Analysis: v=2.4 cv=Wr8rMcfv c=1 sm=1 tr=0 ts=68cc596e cx=c_pps a=CB4LiSf2rd0gKozIdrpkBw==:117 a=CB4LiSf2rd0gKozIdrpkBw==:17 a=yJojWOMRYYMA:10 a=yPCof4ZbAAAA:8 a=QLIaiyCFZkuJlwHvl48A:9 X-Proofpoint-ORIG-GUID: yzU4eNHLhAUfSh4h33V6r2BXOldJckJZ X-Proofpoint-GUID: yzU4eNHLhAUfSh4h33V6r2BXOldJckJZ X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwOTE4MDE3MCBTYWx0ZWRfX+OH6/CZXfYF1 ZQZSd3MY5d1+huXM92tmUuaixGbvXh9eslNEM1bRcbWXduWBJkY9hM7pAwYK1UmVGB6+KtMLK3+ 5xu0OvXnTYTE5X3/j7r0YUT9jTEQIyg7vs2wzGv7et2oYHzPIQqFSONTUbrUfKZtQGE+5Ql2G/m FB+fFTcxSnJqueTYbtn/kFdO7ZXWcwZvUvPEHQAajQYNZXBbU5RIDDKbQMkKIDQGqkR8eZiO5xs q0uwGSCKiMwePOEm2hD3yphFf7LSfGFQnTUqyn0uufzwKaznKzrNA1c2BW91Ht07S88ASQbLxJd y3Z61QWwzOnbaToH1kdrhAuNayIEpInurTQIzwra/DJzb/lInqX9Bhz50sofEw= X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1117,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-09-18_02,2025-09-18_02,2025-03-28_01 On Wed, 10 Sep 2025 21:22:06 +0100 Lorenzo Stoakes wrote: > Update the mem char driver (backing /dev/mem and /dev/zero) to use > f_op->mmap_prepare hook rather than the deprecated f_op->mmap. > > The /dev/zero implementation has a very unique and rather concerning > characteristic in that it converts MAP_PRIVATE mmap() mappings anonymous > when they are, in fact, not. > > The new f_op->mmap_prepare() can support this, but rather than introducing > a helper function to perform this hack (and risk introducing other users), > simply set desc->vm_op to NULL here and add a comment describing what's > going on. > > We also introduce shmem_zero_setup_desc() to allow for the shared mapping > case via an f_op->mmap_prepare() hook, and generalise the code between this > and shmem_zero_setup(). > > We also use the desc->action_error_hook to filter the remap error to > -EAGAIN to keep behaviour consistent. > > Signed-off-by: Lorenzo Stoakes > --- > drivers/char/mem.c | 75 ++++++++++++++++++++++------------------ > include/linux/shmem_fs.h | 3 +- > mm/shmem.c | 40 ++++++++++++++++----- > 3 files changed, 76 insertions(+), 42 deletions(-) > [ ... ] > diff --git a/mm/shmem.c b/mm/shmem.c > index 990e33c6a776..cb6ff00eb4cb 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c [ ... ] > @@ -5920,6 +5925,25 @@ int shmem_zero_setup(struct vm_area_struct *vma) > return 0; > } > > +/** > + * shmem_zero_setup_desc - same as shmem_zero_setup, but determined by VMA > + * descriptor for convenience. > + * @desc: Describes VMA > + * Returns: 0 on success, or error > + */ > +int shmem_zero_setup_desc(struct vm_area_desc *desc) > +{ > + struct file *file = __shmem_zero_setup(desc->start, desc->end, desc->vm_flags); > + > + if (IS_ERR(file)) > + return PTR_ERR(file); > + > + desc->vm_file = file; > + desc->vm_ops = &shmem_anon_vm_ops; > + > + return 0; > +} > + Hi Lorenzo, shmem_zero_setup() does a if (vma->vm_file) fput(vma->vm_file) dance. It looks like we need one here too? -chris