From nobody Sat Oct 4 06:37:49 2025 Received: from mx0b-00069f02.pphosted.com (mx0b-00069f02.pphosted.com [205.220.177.32]) (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 703A51F4176; Wed, 20 Aug 2025 01:05:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=205.220.177.32 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755651959; cv=none; b=FMFIaGxw0lUvm9c3Yo5T+pbNPHnmAzw4nbYZkPU6g+tNRDblRe0QG6hD84D0LWo9iGlbOvSXmjjmpQMKl7NAAy4iC8K8IYl/tARQVpufRBsjbCj1iRJTIxTd+8+puZfToMtPGKrJpsJZ6KlgP4TiZoQ/lyDESsfoFFvP5yPiiu8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755651959; c=relaxed/simple; bh=MffUHMuqtaCzpkhdizzcpJ0sXDdhSU8Tjt+mNcF8NUE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=pRUD9Hf3/pfWqsO3bJcsI3fky6wCeJl/H5G3+X+18regiYNfVORwpY/w2XNl65/lUQSkDc6DhXdAEINiieTya5C26mfIzTZxOtvu9SHbYDWIysdlUDaLH26me6gqUityWKj0/1uHFU5vd5qGDGlpqQMFriIKTthF8XFEMs1a+0E= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=oracle.com; spf=pass smtp.mailfrom=oracle.com; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b=chRqHdL3; arc=none smtp.client-ip=205.220.177.32 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=oracle.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=oracle.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="chRqHdL3" Received: from pps.filterd (m0333520.ppops.net [127.0.0.1]) by mx0b-00069f02.pphosted.com (8.18.1.2/8.18.1.2) with ESMTP id 57JLBntf004717; Wed, 20 Aug 2025 01:04:29 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=cc :content-transfer-encoding:date:from:in-reply-to:message-id :mime-version:references:subject:to; s=corp-2025-04-25; bh=gvtSU 8joP13kEFVRuIji2CS52l0yNsMc//UfkvDFdGU=; b=chRqHdL30O/eJPJFelYIF JxRhsujjXC0JG/oz9/MU5CeqTekl999B56TQbX8LfmRMQBmg3rQn0O2/7XD8OGre kBCg84rUXr3D8TeMSJxqHyPScVo/5uNq/kKaagc8u8oe+YwQSW6IZjYXtu+phYQN ufvs6aXscoBag76SiGkOoUgknXMK56YgqJFwlnEy0r2m5XirmpM9efE5HQfKGnSb FfpImDr2IJHNd9b9GBjYH+qgmaj/vG8JhZG6W0yY1F3g14BALk3pG5VHoX6Z+86i otDMMSxlOPjI4xSZpnxTMq1Pk/wdC30PX0vCpCnhiJsx49iJXEqQ9tPiQ+LTel6N w== Received: from phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com (phxpaimrmta01.appoci.oracle.com [138.1.114.2]) by mx0b-00069f02.pphosted.com (PPS) with ESMTPS id 48n0tqr8aq-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 20 Aug 2025 01:04:28 +0000 (GMT) Received: from pps.filterd (phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com [127.0.0.1]) by phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com (8.18.1.2/8.18.1.2) with ESMTP id 57JN39eS007104; Wed, 20 Aug 2025 01:04:27 GMT Received: from pps.reinject (localhost [127.0.0.1]) by phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com (PPS) with ESMTPS id 48my3q29ng-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 20 Aug 2025 01:04:27 +0000 Received: from phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com (phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com [127.0.0.1]) by pps.reinject (8.17.1.5/8.17.1.5) with ESMTP id 57K14Nd6011685; Wed, 20 Aug 2025 01:04:26 GMT Received: from localhost.localdomain (ca-dev60.us.oracle.com [10.129.136.27]) by phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com (PPS) with ESMTP id 48my3q29gw-2; Wed, 20 Aug 2025 01:04:26 +0000 From: Anthony Yznaga To: linux-mm@kvack.org Cc: akpm@linux-foundation.org, andreyknvl@gmail.com, arnd@arndb.de, bp@alien8.de, brauner@kernel.org, bsegall@google.com, corbet@lwn.net, dave.hansen@linux.intel.com, david@redhat.com, dietmar.eggemann@arm.com, ebiederm@xmission.com, hpa@zytor.com, jakub.wartak@mailbox.org, jannh@google.com, juri.lelli@redhat.com, khalid@kernel.org, liam.howlett@oracle.com, linyongting@bytedance.com, lorenzo.stoakes@oracle.com, luto@kernel.org, markhemm@googlemail.com, maz@kernel.org, mhiramat@kernel.org, mgorman@suse.de, mhocko@suse.com, mingo@redhat.com, muchun.song@linux.dev, neilb@suse.de, osalvador@suse.de, pcc@google.com, peterz@infradead.org, pfalcato@suse.de, rostedt@goodmis.org, rppt@kernel.org, shakeel.butt@linux.dev, surenb@google.com, tglx@linutronix.de, vasily.averin@linux.dev, vbabka@suse.cz, vincent.guittot@linaro.org, viro@zeniv.linux.org.uk, vschneid@redhat.com, willy@infradead.org, x86@kernel.org, xhao@linux.alibaba.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org Subject: [PATCH v3 01/22] mm: Add msharefs filesystem Date: Tue, 19 Aug 2025 18:03:54 -0700 Message-ID: <20250820010415.699353-2-anthony.yznaga@oracle.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20250820010415.699353-1-anthony.yznaga@oracle.com> References: <20250820010415.699353-1-anthony.yznaga@oracle.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-08-19_04,2025-08-14_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 suspectscore=0 mlxlogscore=999 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2508110000 definitions=main-2508200007 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwODE5MDE5NyBTYWx0ZWRfXxAv3h/m+MTfc 0ptiIARYa95maJCEZqJrG3tLLfGpL+aAvAx5WUp1c4PkyP4lb9O2BjnTaVHBUz7+VrN6M2X8Odl /9giLrBYnZUEDrpCesHEZOlRkw1P5OBPFkRxms3GEYaLOFD78Uo8BxIQKjsaT8z5IbGiIgwiWy0 fN6x5Cu2SJbcRrRaX9KjHMIw1aUI8DMevMqW3DsLJduVto3IfZr3FwThOQdIByR0qKOb5V18kUv X7hTq4VMAuoDTt3LolBTn4BF7FbEJ+kkuHfMXBT3iWtuCiTPcoj/ADRlBbAuirJiwkNWSPhlcDG KfHWFnvVrQOdKanevXFtxI0EPCSzYgC7PaRTBFgculdg6jYyEnPjJkMEORformFhMkzIXg285lM GhlZJFYkk7/nK/ZLzIcIL5P8NkG//Q== X-Proofpoint-ORIG-GUID: yRHOcQOSeDi0JpjdrasRvx-vwL1WmHeC X-Proofpoint-GUID: yRHOcQOSeDi0JpjdrasRvx-vwL1WmHeC X-Authority-Analysis: v=2.4 cv=K/p73yWI c=1 sm=1 tr=0 ts=68a51f1c cx=c_pps a=XiAAW1AwiKB2Y8Wsi+sD2Q==:117 a=XiAAW1AwiKB2Y8Wsi+sD2Q==:17 a=2OwXVqhp2XgA:10 a=VwQbUJbxAAAA:8 a=yPCof4ZbAAAA:8 a=Mf_uHGjaqS_lSwFvvQkA:9 a=UhEZJTgQB8St2RibIkdl:22 a=Z5ABNNGmrOfJ6cZ5bIyy:22 a=QOGEsqRv6VhmHaoFNykA:22 Content-Type: text/plain; charset="utf-8" From: Khalid Aziz Add a pseudo filesystem that contains files and page table sharing information that enables processes to share page table entries. This patch adds the basic filesystem that can be mounted, a CONFIG_MSHARE option to enable the feature, and documentation. Signed-off-by: Khalid Aziz Signed-off-by: Anthony Yznaga --- Documentation/filesystems/index.rst | 1 + Documentation/filesystems/msharefs.rst | 96 +++++++++++++++++++++++++ include/uapi/linux/magic.h | 1 + mm/Kconfig | 11 +++ mm/Makefile | 4 ++ mm/mshare.c | 97 ++++++++++++++++++++++++++ 6 files changed, 210 insertions(+) create mode 100644 Documentation/filesystems/msharefs.rst create mode 100644 mm/mshare.c diff --git a/Documentation/filesystems/index.rst b/Documentation/filesystem= s/index.rst index 11a599387266..dcd6605eb228 100644 --- a/Documentation/filesystems/index.rst +++ b/Documentation/filesystems/index.rst @@ -102,6 +102,7 @@ Documentation for filesystem implementations. fuse-passthrough inotify isofs + msharefs nilfs2 nfs/index ntfs3 diff --git a/Documentation/filesystems/msharefs.rst b/Documentation/filesys= tems/msharefs.rst new file mode 100644 index 000000000000..3e5b7d531821 --- /dev/null +++ b/Documentation/filesystems/msharefs.rst @@ -0,0 +1,96 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D +Msharefs - A filesystem to support shared page tables +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D + +What is msharefs? +----------------- + +msharefs is a pseudo filesystem that allows multiple processes to +share page table entries for shared pages. To enable support for +msharefs the kernel must be compiled with CONFIG_MSHARE set. + +msharefs is typically mounted like this:: + + mount -t msharefs none /sys/fs/mshare + +A file created on msharefs creates a new shared region where all +processes mapping that region will map it using shared page table +entries. Once the size of the region has been established via +ftruncate() or fallocate(), the region can be mapped into processes +and ioctls used to map and unmap objects within it. Note that an +msharefs file is a control file and accessing mapped objects within +a shared region through read or write of the file is not permitted. + +How to use mshare +----------------- + +Here are the basic steps for using mshare: + + 1. Mount msharefs on /sys/fs/mshare:: + + mount -t msharefs msharefs /sys/fs/mshare + + 2. mshare regions have alignment and size requirements. Start + address for the region must be aligned to an address boundary and + be a multiple of fixed size. This alignment and size requirement + can be obtained by reading the file ``/sys/fs/mshare/mshare_info`` + which returns a number in text format. mshare regions must be + aligned to this boundary and be a multiple of this size. + + 3. For the process creating an mshare region: + + a. Create a file on /sys/fs/mshare, for example:: + + fd =3D open("/sys/fs/mshare/shareme", + O_RDWR|O_CREAT|O_EXCL, 0600); + + b. Establish the size of the region:: + + fallocate(fd, 0, 0, BUF_SIZE); + + or:: + + ftruncate(fd, BUF_SIZE); + + c. Map some memory in the region:: + + struct mshare_create mcreate; + + mcreate.region_offset =3D 0; + mcreate.size =3D BUF_SIZE; + mcreate.offset =3D 0; + mcreate.prot =3D PROT_READ | PROT_WRITE; + mcreate.flags =3D MAP_ANONYMOUS | MAP_SHARED | MAP_FIXED; + mcreate.fd =3D -1; + + ioctl(fd, MSHAREFS_CREATE_MAPPING, &mcreate); + + d. Map the mshare region into the process:: + + mmap(NULL, BUF_SIZE, + PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); + + e. Write and read to mshared region normally. + + + 4. For processes attaching an mshare region: + + a. Open the msharefs file, for example:: + + fd =3D open("/sys/fs/mshare/shareme", O_RDWR); + + b. Get the size of the mshare region from the file:: + + fstat(fd, &sb); + mshare_size =3D sb.st_size; + + c. Map the mshare region into the process:: + + mmap(NULL, mshare_size, + PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); + + 5. To delete the mshare region:: + + unlink("/sys/fs/mshare/shareme"); diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h index bb575f3ab45e..e53dd6063cba 100644 --- a/include/uapi/linux/magic.h +++ b/include/uapi/linux/magic.h @@ -103,5 +103,6 @@ #define DEVMEM_MAGIC 0x454d444d /* "DMEM" */ #define SECRETMEM_MAGIC 0x5345434d /* "SECM" */ #define PID_FS_MAGIC 0x50494446 /* "PIDF" */ +#define MSHARE_MAGIC 0x4d534852 /* "MSHR" */ =20 #endif /* __LINUX_MAGIC_H__ */ diff --git a/mm/Kconfig b/mm/Kconfig index 4108bcd96784..8b50e9785729 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -1400,6 +1400,17 @@ config PT_RECLAIM config FIND_NORMAL_PAGE def_bool n =20 +config MSHARE + bool "Mshare" + depends on MMU + help + Enable msharefs: A pseudo filesystem that allows multiple processes + to share kernel resources for mapping shared pages. A file created on + msharefs represents a shared region where all processes mapping that + region will map objects within it with shared page table entries and + VMAs. Ioctls are used to configure and map objects into the shared + region. + source "mm/damon/Kconfig" =20 endmenu diff --git a/mm/Makefile b/mm/Makefile index ef54aa615d9d..4af111b29c68 100644 --- a/mm/Makefile +++ b/mm/Makefile @@ -48,6 +48,10 @@ ifdef CONFIG_64BIT mmu-$(CONFIG_MMU) +=3D mseal.o endif =20 +ifdef CONFIG_MSHARE +mmu-$(CONFIG_MMU) +=3D mshare.o +endif + obj-y :=3D filemap.o mempool.o oom_kill.o fadvise.o \ maccess.o page-writeback.o folio-compat.o \ readahead.o swap.o truncate.o vmscan.o shrinker.o \ diff --git a/mm/mshare.c b/mm/mshare.c new file mode 100644 index 000000000000..f703af49ec81 --- /dev/null +++ b/mm/mshare.c @@ -0,0 +1,97 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Enable cooperating processes to share page table between + * them to reduce the extra memory consumed by multiple copies + * of page tables. + * + * This code adds an in-memory filesystem - msharefs. + * msharefs is used to manage page table sharing + * + * + * Copyright (C) 2024 Oracle Corp. All rights reserved. + * Author: Khalid Aziz + * + */ + +#include +#include +#include + +static const struct file_operations msharefs_file_operations =3D { + .open =3D simple_open, +}; + +static const struct super_operations mshare_s_ops =3D { + .statfs =3D simple_statfs, +}; + +static int +msharefs_fill_super(struct super_block *sb, struct fs_context *fc) +{ + struct inode *inode; + + sb->s_blocksize =3D PAGE_SIZE; + sb->s_blocksize_bits =3D PAGE_SHIFT; + sb->s_maxbytes =3D MAX_LFS_FILESIZE; + sb->s_magic =3D MSHARE_MAGIC; + sb->s_op =3D &mshare_s_ops; + sb->s_time_gran =3D 1; + + inode =3D new_inode(sb); + if (!inode) + return -ENOMEM; + + inode->i_ino =3D 1; + inode->i_mode =3D S_IFDIR | 0777; + simple_inode_init_ts(inode); + inode->i_op =3D &simple_dir_inode_operations; + inode->i_fop =3D &simple_dir_operations; + set_nlink(inode, 2); + + sb->s_root =3D d_make_root(inode); + if (!sb->s_root) + return -ENOMEM; + + return 0; +} + +static int +msharefs_get_tree(struct fs_context *fc) +{ + return get_tree_nodev(fc, msharefs_fill_super); +} + +static const struct fs_context_operations msharefs_context_ops =3D { + .get_tree =3D msharefs_get_tree, +}; + +static int +mshare_init_fs_context(struct fs_context *fc) +{ + fc->ops =3D &msharefs_context_ops; + return 0; +} + +static struct file_system_type mshare_fs =3D { + .name =3D "msharefs", + .init_fs_context =3D mshare_init_fs_context, + .kill_sb =3D kill_litter_super, +}; + +static int __init +mshare_init(void) +{ + int ret; + + ret =3D sysfs_create_mount_point(fs_kobj, "mshare"); + if (ret) + return ret; + + ret =3D register_filesystem(&mshare_fs); + if (ret) + sysfs_remove_mount_point(fs_kobj, "mshare"); + + return ret; +} + +core_initcall(mshare_init); --=20 2.47.1