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charset="utf-8" From: Khalid Aziz Add a ram-based filesystem that contains page table sharing information and files that enables processes to share page tables. This patch adds the basic filesystem that can be mounted. Signed-off-by: Khalid Aziz Signed-off-by: Anthony Yznaga --- Documentation/filesystems/msharefs.rst | 107 +++++++++++++++++++++++++ include/uapi/linux/magic.h | 1 + mm/Makefile | 2 +- mm/mshare.c | 97 ++++++++++++++++++++++ 4 files changed, 206 insertions(+), 1 deletion(-) create mode 100644 Documentation/filesystems/msharefs.rst create mode 100644 mm/mshare.c diff --git a/Documentation/filesystems/msharefs.rst b/Documentation/filesys= tems/msharefs.rst new file mode 100644 index 000000000000..727cda663b0b --- /dev/null +++ b/Documentation/filesystems/msharefs.rst @@ -0,0 +1,107 @@ +.. 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 + +msharefs is a ram-based filesystem that allows multiple processes to +share page table entries for shared pages. + +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. ioctls are used to initialize or retrieve the start address +and size of a shared region and to map objects in the shared +region. It is important to note that an msharefs file is a control +file for the shared region and does not contain the contents +of the region itself. + +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: + +.. code-block:: c + + fd =3D open("/sys/fs/mshare/shareme", + O_RDWR|O_CREAT|O_EXCL, 0600); + +b. Establish the starting address and size of the region: + +.. code-block:: c + + struct mshare_info minfo; + + minfo.start =3D TB(2); + minfo.size =3D BUFFER_SIZE; + ioctl(fd, MSHAREFS_SET_SIZE, &minfo); + +c. Map some memory in the region: + +.. code-block:: c + + struct mshare_create mcreate; + + mcreate.addr =3D TB(2); + mcreate.size =3D BUFFER_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: + +.. code-block:: c + + mmap((void *)TB(2), 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 file on msharefs, for example: + +.. code-block:: c + + fd =3D open("/sys/fs/mshare/shareme", O_RDWR); + +b. Get information about mshare'd region from the file: + +.. code-block:: c + + struct mshare_info minfo; + + ioctl(fd, MSHAREFS_GET_SIZE, &minfo); + +c. Map the mshare'd region into the process: + +.. code-block:: c + + mmap(minfo.start, minfo.size, + PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); + +5. To delete the mshare region: + +.. code-block:: c + + 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/Makefile b/mm/Makefile index d2915f8c9dc0..956137de9e1f 100644 --- a/mm/Makefile +++ b/mm/Makefile @@ -45,7 +45,7 @@ mmu-$(CONFIG_MMU) +=3D process_vm_access.o endif =20 ifdef CONFIG_64BIT -mmu-$(CONFIG_MMU) +=3D mseal.o +mmu-$(CONFIG_MMU) +=3D mseal.o mshare.o endif =20 obj-y :=3D filemap.o mempool.o oom_kill.o fadvise.o \ diff --git a/mm/mshare.c b/mm/mshare.c new file mode 100644 index 000000000000..d5d8e2530e5a --- /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, + .llseek =3D no_llseek, +}; + +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_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 2.43.5