[PATCH 2/4] mm: introduce external memory hinting API

[Minchan Kim <minchan@kernel.org>]

There are usecases that System Management Software(SMS) want to give
a memory hint to other processes because it's not known to the
application. In the case of Android, ActivityManagerService daemon
manges app's life cycle and that daemon must be able to initiate
reclaim on its own without any app involvement.

To solve the issue, this patch introduces new syscall process_madvise(2).
It uses pidfd of an external processs to give the hint.

 int process_madvise(int pidfd, void *addr, size_t length, int advise,
			unsigned long flag);

Since it could affect other process's address range, only privileged
process(CAP_SYS_PTRACE) or something else(e.g., being the same UID)
gives it the right to ptrace the process could use it successfully.
The flag argument is reserved for future use if we need to extend the
API.

Supporting all hints madvise has/will supported/support to process_madvise
is rather risky. Because we are not sure all hints make sense from external
process and implementation for the hint may rely on the caller being
in the current context so it could be error-prone. Thus, I just limited
hints as MADV_[COLD|PAGEOUT] in this patch.

If someone want to add other hints, we could hear hear the usecase and
review it for each hint. It's more safe for maintainace rather than
introducing a buggy syscall but hard to fix it later.

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 arch/alpha/kernel/syscalls/syscall.tbl      |  1 +
 arch/arm/tools/syscall.tbl                  |  1 +
 arch/arm64/include/asm/unistd.h             |  2 +-
 arch/arm64/include/asm/unistd32.h           |  2 +
 arch/ia64/kernel/syscalls/syscall.tbl       |  1 +
 arch/m68k/kernel/syscalls/syscall.tbl       |  1 +
 arch/microblaze/kernel/syscalls/syscall.tbl |  1 +
 arch/mips/kernel/syscalls/syscall_n32.tbl   |  1 +
 arch/mips/kernel/syscalls/syscall_n64.tbl   |  1 +
 arch/parisc/kernel/syscalls/syscall.tbl     |  1 +
 arch/powerpc/kernel/syscalls/syscall.tbl    |  1 +
 arch/s390/kernel/syscalls/syscall.tbl       |  1 +
 arch/sh/kernel/syscalls/syscall.tbl         |  1 +
 arch/sparc/kernel/syscalls/syscall.tbl      |  1 +
 arch/x86/entry/syscalls/syscall_32.tbl      |  1 +
 arch/x86/entry/syscalls/syscall_64.tbl      |  1 +
 arch/xtensa/kernel/syscalls/syscall.tbl     |  1 +
 include/linux/syscalls.h                    |  2 +
 include/uapi/asm-generic/unistd.h           |  5 +-
 kernel/sys_ni.c                             |  1 +
 mm/madvise.c                                | 64 +++++++++++++++++++++
 21 files changed, 89 insertions(+), 2 deletions(-)

diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl
index e56950f23b49..776c61803315 100644
--- a/arch/alpha/kernel/syscalls/syscall.tbl
+++ b/arch/alpha/kernel/syscalls/syscall.tbl
@@ -477,3 +477,4 @@
 # 545 reserved for clone3
 546	common	watch_devices			sys_watch_devices
 547	common	openat2				sys_openat2
+548	common	process_madvise			sys_process_madvise
diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl
index 7fb2f4d59210..a43381542276 100644
--- a/arch/arm/tools/syscall.tbl
+++ b/arch/arm/tools/syscall.tbl
@@ -451,3 +451,4 @@
 435	common	clone3				sys_clone3
 436	common	watch_devices			sys_watch_devices
 437	common	openat2				sys_openat2
+438	common	process_madvise			sys_process_madvise
diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h
index 8aa00ccb0b96..b722e47377a5 100644
--- a/arch/arm64/include/asm/unistd.h
+++ b/arch/arm64/include/asm/unistd.h
@@ -38,7 +38,7 @@
 #define __ARM_NR_compat_set_tls		(__ARM_NR_COMPAT_BASE + 5)
 #define __ARM_NR_COMPAT_END		(__ARM_NR_COMPAT_BASE + 0x800)
 
-#define __NR_compat_syscalls		438
+#define __NR_compat_syscalls		439
 #endif
 
 #define __ARCH_WANT_SYS_CLONE
diff --git a/arch/arm64/include/asm/unistd32.h b/arch/arm64/include/asm/unistd32.h
index 31f0ce25719e..5c82557d408f 100644
--- a/arch/arm64/include/asm/unistd32.h
+++ b/arch/arm64/include/asm/unistd32.h
@@ -883,6 +883,8 @@ __SYSCALL(__NR_clone3, sys_clone3)
 __SYSCALL(__NR_watch_devices, sys_watch_devices)
 #define __NR_openat2 437
 __SYSCALL(__NR_openat2, sys_openat2)
+#define __NR_openat2 438
+__SYSCALL(__NR_process_madvise, process_madvise)
 
 /*
  * Please add new compat syscalls above this comment and update
diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl
index b9aa59931905..c156abc9a298 100644
--- a/arch/ia64/kernel/syscalls/syscall.tbl
+++ b/arch/ia64/kernel/syscalls/syscall.tbl
@@ -358,3 +358,4 @@
 # 435 reserved for clone3
 436	common	watch_devices			sys_watch_devices
 437	common	openat2				sys_openat2
+438	common	process_madvise			sys_process_madvise
diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
index 868c1ef89d35..5b6034b6650f 100644
--- a/arch/m68k/kernel/syscalls/syscall.tbl
+++ b/arch/m68k/kernel/syscalls/syscall.tbl
@@ -437,3 +437,4 @@
 # 435 reserved for clone3
 436	common	watch_devices			sys_watch_devices
 437	common	openat2				sys_openat2
+438	common	process_madvise			sys_process_madvise
diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl
index 544b4cef18b3..4bef584af09c 100644
--- a/arch/microblaze/kernel/syscalls/syscall.tbl
+++ b/arch/microblaze/kernel/syscalls/syscall.tbl
@@ -443,3 +443,4 @@
 435	common	clone3				sys_clone3
 436	common	watch_devices			sys_watch_devices
 437	common	openat2				sys_openat2
+438	common	process_madvise			sys_process_madvise
diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl
index 05e8aee5dae7..94fbd0fcccce 100644
--- a/arch/mips/kernel/syscalls/syscall_n32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n32.tbl
@@ -376,3 +376,4 @@
 435	n32	clone3				__sys_clone3
 436	n32	watch_devices			sys_watch_devices
 437	n32	openat2				sys_openat2
+437	n32	process_madivse			sys_process_madvise
diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl
index 24d6c01328fb..4e6982c429d5 100644
--- a/arch/mips/kernel/syscalls/syscall_n64.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n64.tbl
@@ -352,3 +352,4 @@
 435	n64	clone3				__sys_clone3
 436	n64	watch_devices			sys_watch_devices
 437	n64	openat2				sys_openat2
+437	n64	process_madvise			sys_process_madvise
diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl
index 4b5f77a4e1a2..3aa990caf9dc 100644
--- a/arch/parisc/kernel/syscalls/syscall.tbl
+++ b/arch/parisc/kernel/syscalls/syscall.tbl
@@ -435,3 +435,4 @@
 435	common	clone3				sys_clone3_wrapper
 436	common	watch_devices			sys_watch_devices
 437	common	openat2				sys_openat2
+437	common	process_madvise			sys_process_madvise
diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
index 9716dc85a517..30e727a23f33 100644
--- a/arch/powerpc/kernel/syscalls/syscall.tbl
+++ b/arch/powerpc/kernel/syscalls/syscall.tbl
@@ -519,3 +519,4 @@
 435	nospu	clone3				ppc_clone3
 436	common	watch_devices			sys_watch_devices
 437	common	openat2				sys_openat2
+437	common	process_madvise			sys_process_madvise
diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl
index 7da330f8b03e..75722e5ff496 100644
--- a/arch/s390/kernel/syscalls/syscall.tbl
+++ b/arch/s390/kernel/syscalls/syscall.tbl
@@ -440,3 +440,4 @@
 435  common	clone3			sys_clone3			sys_clone3
 436  common	watch_devices		sys_watch_devices		sys_watch_devices
 437  common	openat2			sys_openat2			sys_openat2
+437  common	process_madvise		sys_process_madvise		sys_process_madvise
diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl
index bb7e68e25337..7d7bc7befad3 100644
--- a/arch/sh/kernel/syscalls/syscall.tbl
+++ b/arch/sh/kernel/syscalls/syscall.tbl
@@ -440,3 +440,4 @@
 # 435 reserved for clone3
 436	common	watch_devices			sys_watch_devices
 437	common	openat2				sys_openat2
+437	common	process_madvise			sys_process_madvise
diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl
index 646a1fad7218..581d331ff62f 100644
--- a/arch/sparc/kernel/syscalls/syscall.tbl
+++ b/arch/sparc/kernel/syscalls/syscall.tbl
@@ -483,3 +483,4 @@
 # 435 reserved for clone3
 436	common	watch_devices			sys_watch_devices
 437	common	openat2			sys_openat2
+437	common	process_madvise		sys_process_madvise
diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 57c53acee290..76a2c266fe7e 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -442,3 +442,4 @@
 435	i386	clone3			sys_clone3			__ia32_sys_clone3
 436	i386	watch_devices		sys_watch_devices		__ia32_sys_watch_devices
 437	i386	openat2			sys_openat2			__ia32_sys_openat2
+438	i386	process_madvise		sys_process_madvise		__ia32_sys_process_madvise
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 1dd8d21f6500..b697cd8620cb 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -359,6 +359,7 @@
 435	common	clone3			__x64_sys_clone3/ptregs
 436	common	watch_devices		__x64_sys_watch_devices
 437	common	openat2			__x64_sys_openat2
+438	common	process_madvise		__x64_sys_process_madvise
 
 #
 # x32-specific system call numbers start at 512 to avoid cache impact
diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl
index 0f48ab7bd75b..2e9813ecfd7d 100644
--- a/arch/xtensa/kernel/syscalls/syscall.tbl
+++ b/arch/xtensa/kernel/syscalls/syscall.tbl
@@ -408,3 +408,4 @@
 435	common	clone3				sys_clone3
 436	common	watch_devices			sys_watch_devices
 437	common	openat2				sys_openat2
+438	common	process_madvise			sys_process_madvise
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 433c8c85636e..1b58a11ff49f 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -877,6 +877,8 @@ asmlinkage long sys_munlockall(void);
 asmlinkage long sys_mincore(unsigned long start, size_t len,
 				unsigned char __user * vec);
 asmlinkage long sys_madvise(unsigned long start, size_t len, int behavior);
+asmlinkage long sys_process_madvise(int pidfd, unsigned long start,
+			size_t len, int behavior, unsigned long flags);
 asmlinkage long sys_remap_file_pages(unsigned long start, unsigned long size,
 			unsigned long prot, unsigned long pgoff,
 			unsigned long flags);
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index 33f3856a9c3c..4bcd8d366f38 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -856,8 +856,11 @@ __SYSCALL(__NR_watch_devices, sys_watch_devices)
 #define __NR_openat2 437
 __SYSCALL(__NR_openat2, sys_openat2)
 
+#define __NR_openat2 438
+__SYSCALL(__NR_process_madvise, sys_process_madvise)
+
 #undef __NR_syscalls
-#define __NR_syscalls 438
+#define __NR_syscalls 439
 
 /*
  * 32 bit systems traditionally used different
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 0e9b275260f8..10ce5eac8b4b 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -281,6 +281,7 @@ COND_SYSCALL(mlockall);
 COND_SYSCALL(munlockall);
 COND_SYSCALL(mincore);
 COND_SYSCALL(madvise);
+COND_SYSCALL(process_madvise);
 COND_SYSCALL(remap_file_pages);
 COND_SYSCALL(mbind);
 COND_SYSCALL_COMPAT(mbind);
diff --git a/mm/madvise.c b/mm/madvise.c
index 0c901de531e4..e15dfb4df7bf 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -17,6 +17,7 @@
 #include <linux/falloc.h>
 #include <linux/fadvise.h>
 #include <linux/sched.h>
+#include <linux/sched/mm.h>
 #include <linux/ksm.h>
 #include <linux/fs.h>
 #include <linux/file.h>
@@ -993,6 +994,18 @@ madvise_behavior_valid(int behavior)
 	}
 }
 
+static bool
+process_madvise_behavior_valid(int behavior)
+{
+	switch (behavior) {
+	case MADV_COLD:
+	case MADV_PAGEOUT:
+		return true;
+	default:
+		return false;
+	}
+}
+
 /*
  * madvise_common - request behavior hint to address range of the target process
  *
@@ -1169,3 +1182,54 @@ SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
 {
 	return madvise_common(current, current->mm, start, len_in, behavior);
 }
+
+SYSCALL_DEFINE5(process_madvise, int, pidfd, unsigned long, start,
+		size_t, len_in, int, behavior, unsigned long, flags)
+{
+	int ret;
+	struct fd f;
+	struct pid *pid;
+	struct task_struct *task;
+	struct mm_struct *mm;
+
+	if (flags != 0)
+		return -EINVAL;
+
+	if (!process_madvise_behavior_valid(behavior))
+		return -EINVAL;
+
+	f = fdget(pidfd);
+	if (!f.file)
+		return -EBADF;
+
+	pid = pidfd_pid(f.file);
+	if (IS_ERR(pid)) {
+		ret = PTR_ERR(pid);
+		goto err;
+	}
+
+	rcu_read_lock();
+	task = pid_task(pid, PIDTYPE_PID);
+	if (!task) {
+		rcu_read_unlock();
+		ret = -ESRCH;
+		goto err;
+	}
+
+	get_task_struct(task);
+	rcu_read_unlock();
+
+	mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS);
+	if (IS_ERR_OR_NULL(mm)) {
+		ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
+		goto release_task;
+	}
+
+	ret = madvise_common(task, mm, start, len_in, behavior);
+	mmput(mm);
+release_task:
+	put_task_struct(task);
+err:
+	fdput(f);
+	return ret;
+}
-- 
2.25.0.rc1.283.g88dfdc4193-goog