[RFC PATCH 2/4] Introduce fbind syscall

[Shivank Garg <shivankg@amd.com>]

The new fbind syscall sets the NUMA memory policy for file-backed memory
and has following signature:

long fbind(unsigned int fd, unsigned long mode,
                const unsigned long nodemask[(.maxnode + ULONG_WIDTH - 1)
                                               / ULONG_WIDTH],
                unsigned long maxnode, unsigned int flags);

fbind behaves similar to mbind except that it takes file descriptor as
input instead of address ranges.

TODO:
1. Support fbind syscall on all architectures.
2. Expand commit msg and add documentation.
3. clean-up the code.

[Shivansh: add create_mpol_from_args()]
Signed-off-by: Shivansh Dhiman <shivansh.dhiman@amd.com>
Signed-off-by: Shivank Garg <shivankg@amd.com>
---
 arch/x86/entry/syscalls/syscall_32.tbl |  1 +
 arch/x86/entry/syscalls/syscall_64.tbl |  1 +
 include/linux/fs.h                     |  3 ++
 include/linux/mempolicy.h              |  3 ++
 include/linux/syscalls.h               |  3 ++
 include/uapi/asm-generic/unistd.h      |  5 ++-
 kernel/sys_ni.c                        |  1 +
 mm/Makefile                            |  2 +-
 mm/fbind.c                             | 49 +++++++++++++++++++++++
 mm/mempolicy.c                         | 55 ++++++++++++++++++++++++++
 10 files changed, 121 insertions(+), 2 deletions(-)
 create mode 100644 mm/fbind.c

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 534c74b14fab..0660ce6d08d8 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -468,3 +468,4 @@
 460	i386	lsm_set_self_attr	sys_lsm_set_self_attr
 461	i386	lsm_list_modules	sys_lsm_list_modules
 462	i386	mseal 			sys_mseal
+463	i386	fbind			sys_fbind
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 7093ee21c0d1..9794347cc2e6 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -386,6 +386,7 @@
 460	common	lsm_set_self_attr	sys_lsm_set_self_attr
 461	common	lsm_list_modules	sys_lsm_list_modules
 462 	common  mseal			sys_mseal
+463	common	fbind			sys_fbind
 
 #
 # Due to a historical design error, certain syscalls are numbered differently
diff --git a/include/linux/fs.h b/include/linux/fs.h
index fd34b5755c0b..42042b62bdcd 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2058,6 +2058,9 @@ struct file_operations {
 				   struct file *file_out, loff_t pos_out,
 				   loff_t len, unsigned int remap_flags);
 	int (*fadvise)(struct file *, loff_t, loff_t, int);
+#ifdef CONFIG_NUMA
+	int (*set_policy)(struct file *, struct mempolicy *);
+#endif
 	int (*uring_cmd)(struct io_uring_cmd *ioucmd, unsigned int issue_flags);
 	int (*uring_cmd_iopoll)(struct io_uring_cmd *, struct io_comp_batch *,
 				unsigned int poll_flags);
diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
index 1add16f21612..b9023f6246a7 100644
--- a/include/linux/mempolicy.h
+++ b/include/linux/mempolicy.h
@@ -299,4 +299,7 @@ static inline bool mpol_is_preferred_many(struct mempolicy *pol)
 }
 
 #endif /* CONFIG_NUMA */
+struct mempolicy *create_mpol_from_args(unsigned char mode,
+					const unsigned long __user *nmask,
+					unsigned short maxnode);
 #endif
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 4bcf6754738d..2dc686921b9f 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -502,6 +502,9 @@ asmlinkage long sys_readlinkat(int dfd, const char __user *path, char __user *bu
 asmlinkage long sys_newfstatat(int dfd, const char __user *filename,
 			       struct stat __user *statbuf, int flag);
 asmlinkage long sys_newfstat(unsigned int fd, struct stat __user *statbuf);
+asmlinkage long sys_fbind(unsigned int fd, unsigned long mode,
+			const unsigned long __user *nmask,
+			unsigned long maxnode, unsigned int flags);
 #if defined(__ARCH_WANT_STAT64) || defined(__ARCH_WANT_COMPAT_STAT64)
 asmlinkage long sys_fstat64(unsigned long fd, struct stat64 __user *statbuf);
 asmlinkage long sys_fstatat64(int dfd, const char __user *filename,
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index 5bf6148cac2b..550730f36dae 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -841,8 +841,11 @@ __SYSCALL(__NR_lsm_list_modules, sys_lsm_list_modules)
 #define __NR_mseal 462
 __SYSCALL(__NR_mseal, sys_mseal)
 
+#define __NR_fbind 463
+__SYSCALL(__NR_fbind, sys_fbind)
+
 #undef __NR_syscalls
-#define __NR_syscalls 463
+#define __NR_syscalls 464
 
 /*
  * 32 bit systems traditionally used different
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index c00a86931f8c..f57350e581f6 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -195,6 +195,7 @@ COND_SYSCALL(move_pages);
 COND_SYSCALL(set_mempolicy_home_node);
 COND_SYSCALL(cachestat);
 COND_SYSCALL(mseal);
+COND_SYSCALL(fbind);
 
 COND_SYSCALL(perf_event_open);
 COND_SYSCALL(accept4);
diff --git a/mm/Makefile b/mm/Makefile
index d2915f8c9dc0..ba339ddc0be2 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -79,7 +79,7 @@ obj-$(CONFIG_ZSWAP)	+= zswap.o
 obj-$(CONFIG_HAS_DMA)	+= dmapool.o
 obj-$(CONFIG_HUGETLBFS)	+= hugetlb.o
 obj-$(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP)	+= hugetlb_vmemmap.o
-obj-$(CONFIG_NUMA) 	+= mempolicy.o
+obj-$(CONFIG_NUMA) 	+= mempolicy.o fbind.o
 obj-$(CONFIG_SPARSEMEM)	+= sparse.o
 obj-$(CONFIG_SPARSEMEM_VMEMMAP) += sparse-vmemmap.o
 obj-$(CONFIG_MMU_NOTIFIER) += mmu_notifier.o
diff --git a/mm/fbind.c b/mm/fbind.c
new file mode 100644
index 000000000000..85ec7d13345c
--- /dev/null
+++ b/mm/fbind.c
@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  Implement fbind() syscall.
+ *
+ *  Copyright (c) 2024 AMD
+ *
+ *  Author: Shivank Garg <shivankg@amd.com>
+ */
+
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/mempolicy.h>
+#include <linux/syscalls.h>
+
+static long do_fbind(unsigned int fd, unsigned long mode,
+		const unsigned long __user *nmask,
+		unsigned long maxnode, unsigned int flags)
+{
+	struct mempolicy *mpol;
+	struct fd f;
+	int ret;
+
+	f = fdget(fd);
+	if (!f.file)
+		return -EBADF;
+
+	mpol = create_mpol_from_args(mode, nmask, maxnode);
+	if (IS_ERR_OR_NULL(mpol)) {
+		ret = PTR_ERR(mpol);
+		goto out_putf;
+	}
+
+	if (f.file->f_op->set_policy)
+		ret = f.file->f_op->set_policy(f.file, mpol);
+	else
+		ret = -EOPNOTSUPP;
+
+	mpol_put(mpol);
+out_putf:
+	fdput(f);
+	return ret;
+}
+
+SYSCALL_DEFINE5(fbind, unsigned int, fd, unsigned long, mode,
+		const unsigned long __user *, nmask,
+		unsigned long, maxnode, unsigned int, flags)
+{
+	return do_fbind(fd, mode, nmask, maxnode, flags);
+}
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index b858e22b259d..3a697080ecad 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -3557,3 +3557,58 @@ static int __init mempolicy_sysfs_init(void)
 
 late_initcall(mempolicy_sysfs_init);
 #endif /* CONFIG_SYSFS */
+
+/**
+ * create_mpol_from_args - create a mempolicy structure from args
+ * @mode:  NUMA memory policy mode
+ * @nmask:  bitmask of NUMA nodes
+ * @maxnode:  number of bits in the nodes bitmask
+ *
+ * Create a mempolicy from given nodemask and memory policy such as
+ * default, preferred, interleave or bind.
+ *
+ * Return: error encoded in a pointer or memory policy on success.
+ */
+struct mempolicy *create_mpol_from_args(unsigned char mode,
+					const unsigned long __user *nmask,
+					unsigned short maxnode)
+{
+	struct mm_struct *mm = current->mm;
+	unsigned short mode_flags;
+	struct mempolicy *mpol;
+	nodemask_t nodes;
+	int lmode = mode;
+	int err = -ENOMEM;
+
+	err = sanitize_mpol_flags(&lmode, &mode_flags);
+	if (err)
+		return ERR_PTR(err);
+
+	err = get_nodes(&nodes, nmask, maxnode);
+	if (err)
+		return ERR_PTR(err);
+
+	mpol = mpol_new(mode, mode_flags, &nodes);
+	if (IS_ERR_OR_NULL(mpol))
+		return mpol;
+
+	NODEMASK_SCRATCH(scratch);
+	if (!scratch) {
+		err = -ENOMEM;
+		goto err_out;
+	}
+
+	mmap_write_lock(mm);
+	err = mpol_set_nodemask(mpol, &nodes, scratch);
+	mmap_write_unlock(mm);
+	NODEMASK_SCRATCH_FREE(scratch);
+
+	if (err)
+		goto err_out;
+
+	return mpol;
+
+err_out:
+	mpol_put(mpol);
+	return ERR_PTR(err);
+}
-- 
2.34.1