On Wed, Jun 29, 2022 at 04:53:52PM -0600, Khalid Aziz wrote: > 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 <khalid.aziz@xxxxxxxxxx> > --- > Documentation/filesystems/msharefs.rst | 19 +++++ > include/uapi/linux/magic.h | 1 + > mm/Makefile | 2 +- > mm/mshare.c | 103 +++++++++++++++++++++++++ > 4 files changed, 124 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/filesystems/msharefs.rst > new file mode 100644 > index 000000000000..fd161f67045d > --- /dev/null > +++ b/Documentation/filesystems/msharefs.rst > @@ -0,0 +1,19 @@ > +.. SPDX-License-Identifier: GPL-2.0 > + > +===================================================== > +msharefs - a filesystem to support shared page tables > +===================================================== > + > +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 > + > +When a process calls mshare syscall with a name for the shared address > +range, You mean creat()? > a file with the same name is created under msharefs with that > +name. This file can be opened by another process, if permissions > +allow, to query the addresses shared under this range. These files are > +removed by mshare_unlink syscall and can not be deleted directly. Oh? > +Hence these files are created as immutable files. > diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h > index f724129c0425..2a57a6ec6f3e 100644 > --- a/include/uapi/linux/magic.h > +++ b/include/uapi/linux/magic.h > @@ -105,5 +105,6 @@ > #define Z3FOLD_MAGIC 0x33 > #define PPC_CMM_MAGIC 0xc7571590 > #define SECRETMEM_MAGIC 0x5345434d /* "SECM" */ > +#define MSHARE_MAGIC 0x4d534852 /* "MSHR" */ > > #endif /* __LINUX_MAGIC_H__ */ > diff --git a/mm/Makefile b/mm/Makefile > index 6f9ffa968a1a..51a2ab9080d9 100644 > --- a/mm/Makefile > +++ b/mm/Makefile > @@ -37,7 +37,7 @@ CFLAGS_init-mm.o += $(call cc-disable-warning, override-init) > CFLAGS_init-mm.o += $(call cc-disable-warning, initializer-overrides) > > mmu-y := nommu.o > -mmu-$(CONFIG_MMU) := highmem.o memory.o mincore.o \ > +mmu-$(CONFIG_MMU) := highmem.o memory.o mincore.o mshare.o \ > mlock.o mmap.o mmu_gather.o mprotect.o mremap.o \ > msync.o page_vma_mapped.o pagewalk.o \ > pgtable-generic.o rmap.o vmalloc.o > diff --git a/mm/mshare.c b/mm/mshare.c > new file mode 100644 > index 000000000000..c8fab3869bab > --- /dev/null > +++ b/mm/mshare.c Filesystems are usually supposed to live under fs/; is there some reason to put it in mm/? I guess shmfs is in mm so maybe this isn't much of an objection. Also, should this fs be selectable via a Kconfig option? --D > @@ -0,0 +1,103 @@ > +// SPDX-License-Identifier: GPL-2.0-only > +/* > + * Enable copperating 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) 2022 Oracle Corp. All rights reserved. > + * Author: Khalid Aziz <khalid.aziz@xxxxxxxxxx> > + * > + */ > + > +#include <linux/fs.h> > +#include <linux/mount.h> > +#include <linux/syscalls.h> > +#include <linux/uaccess.h> > +#include <linux/pseudo_fs.h> > +#include <linux/fileattr.h> > +#include <uapi/linux/magic.h> > +#include <uapi/linux/limits.h> > + > +static struct super_block *msharefs_sb; > + > +static const struct file_operations msharefs_file_operations = { > + .open = simple_open, > + .llseek = no_llseek, > +}; > + > +static int > +msharefs_d_hash(const struct dentry *dentry, struct qstr *qstr) > +{ > + unsigned long hash = init_name_hash(dentry); > + const unsigned char *s = qstr->name; > + unsigned int len = qstr->len; > + > + while (len--) > + hash = partial_name_hash(*s++, hash); > + qstr->hash = end_name_hash(hash); > + return 0; > +} > + > +static const struct dentry_operations msharefs_d_ops = { > + .d_hash = msharefs_d_hash, > +}; > + > +static int > +msharefs_fill_super(struct super_block *sb, struct fs_context *fc) > +{ > + static const struct tree_descr empty_descr = {""}; > + int err; > + > + sb->s_d_op = &msharefs_d_ops; > + err = simple_fill_super(sb, MSHARE_MAGIC, &empty_descr); > + if (err) > + return err; > + > + msharefs_sb = sb; > + return 0; > +} > + > +static int > +msharefs_get_tree(struct fs_context *fc) > +{ > + return get_tree_single(fc, msharefs_fill_super); > +} > + > +static const struct fs_context_operations msharefs_context_ops = { > + .get_tree = msharefs_get_tree, > +}; > + > +static int > +mshare_init_fs_context(struct fs_context *fc) > +{ > + fc->ops = &msharefs_context_ops; > + return 0; > +} > + > +static struct file_system_type mshare_fs = { > + .name = "msharefs", > + .init_fs_context = mshare_init_fs_context, > + .kill_sb = kill_litter_super, > +}; > + > +static int > +mshare_init(void) > +{ > + int ret = 0; > + > + ret = sysfs_create_mount_point(fs_kobj, "mshare"); > + if (ret) > + return ret; > + > + ret = register_filesystem(&mshare_fs); > + if (ret) > + sysfs_remove_mount_point(fs_kobj, "mshare"); > + > + return ret; > +} > + > +fs_initcall(mshare_init); > -- > 2.32.0 >