BACKPORT: mm/madvise: introduce process_madvise() syscall: an external memory hinting API

There is usecase that System Management Software(SMS) want to give
a memory hint like MADV_[COLD|PAGEEOUT] to other processes and
in the case of Android, it is the ActivityManagerService.

It's similar in spirit to madvise(MADV_WONTNEED), but the information
required to make the reclaim decision is not known to the app. Instead,
it is known to the centralized userspace daemon(ActivityManagerService),
and that daemon must be able to initiate reclaim on its own without
any app involvement.

To solve the issue, this patch introduces a new syscall process_madvise(2).
It uses pidfd of an external process 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.

I think 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 safer for maintenance rather than
introducing a buggy syscall but hard to fix it later.

[1] https://developer.android.com/topic/performance/memory"
[2] process_getinfo for getting the cookie which is updated whenever
    vma of process address layout are changed - Daniel Colascione
- https://lore.kernel.org/lkml/20190520035254.57579-1-minchan@kernel.org/T/#m7694416fd179b2066a2c62b5b139b14e3894e224
[3] anonymous fd which is used for the object(i.e., address range)
    validation - Michal Hocko
- https://lore.kernel.org/lkml/20200120112722.GY18451@dhcp22.suse.cz/

Link: http://lkml.kernel.org/r/20200302193630.68771-3-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Christian Brauner <christian@brauner.io>
Cc: Daniel Colascione <dancol@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: John Dias <joaodias@google.com>
Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oleksandr Natalenko <oleksandr@redhat.com>
Cc: Sandeep Patil <sspatil@google.com>
Cc: SeongJae Park <sj38.park@gmail.com>
Cc: SeongJae Park <sjpark@amazon.de>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Sonny Rao <sonnyrao@google.com>
Cc: Tim Murray <timmurray@google.com>
Cc: <linux-man@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

(cherry picked from commit ecb8ac8b1f146915aa6b96449b66dd48984caacc)

Conflicts:
    arch/alpha/kernel/syscalls/syscall.tbl
    arch/ia64/kernel/syscalls/syscall.tbl
    arch/m68k/kernel/syscalls/syscall.tbl
    arch/microblaze/kernel/syscalls/syscall.tbl
    arch/mips/kernel/syscalls/syscall_n32.tbl
    arch/mips/kernel/syscalls/syscall_n64.tbl
    arch/parisc/kernel/syscalls/syscall.tbl
    arch/powerpc/kernel/syscalls/syscall.tbl
    arch/s390/kernel/syscalls/syscall.tbl
    arch/sh/kernel/syscalls/syscall.tbl
    arch/sparc/kernel/syscalls/syscall.tbl
    mm/madvise.c

1. __NR_compat_syscalls in arch/arm64/include/asm/unistd.h modified to match latest version to avoid
clobbering old number.
2. Dropped syscall.tbl, syscall_n32, syscall_n64 files for architectures
not present in current kernel.
3. __NR_process_madvise in arch/arm64/include/asm/unistd32.h modified to
match latest mm tree.
4. Added include for uio.h lib which is needed for UIO_FASTIOV and iovec

Bug: 153444106
Test: Built kernel
Signed-off-by: Edgar Arriaga García <edgararriaga@google.com>

Change-Id: Icfff940abebcf290c3111239989ed40a407cf2a6
Signed-off-by: azrim <mirzaspc@gmail.com>

arch/arm/tools/syscall.tbl

@@ -414,3 +414,4 @@
 397	common	statx			sys_statx
 424	common	pidfd_send_signal	sys_pidfd_send_signal
 434	common	pidfd_open		sys_pidfd_open
+440	common	process_madvise		sys_process_madvise

arch/arm64/include/asm/unistd.h

@@ -43,7 +43,7 @@
 #define __ARM_NR_compat_cacheflush	(__ARM_NR_COMPAT_BASE+2)
 #define __ARM_NR_compat_set_tls		(__ARM_NR_COMPAT_BASE+5)
 
-#define __NR_compat_syscalls		435
+#define __NR_compat_syscalls		441
 #endif
 
 #define __ARCH_WANT_SYS_CLONE

arch/arm64/include/asm/unistd32.h

@@ -821,6 +821,8 @@ __SYSCALL(__NR_statx, sys_statx)
 __SYSCALL(__NR_pidfd_send_signal, sys_pidfd_send_signal)
 #define __NR_pidfd_open 434
 __SYSCALL(__NR_pidfd_open, sys_pidfd_open)
+#define __NR_process_madvise 440
+__SYSCALL(__NR_process_madvise, sys_process_madvise)
 
 /*
  * Please add new compat syscalls above this comment and update

arch/x86/entry/syscalls/syscall_32.tbl

@@ -393,3 +393,4 @@
 384	i386	arch_prctl		sys_arch_prctl			compat_sys_arch_prctl
 424	i386	pidfd_send_signal	sys_pidfd_send_signal
 434	i386	pidfd_open		sys_pidfd_open
+440	i386	process_madvise		sys_process_madvise     sys_process_madvise

arch/x86/entry/syscalls/syscall_64.tbl

@@ -341,6 +341,7 @@
 332	common	statx			sys_statx
 424	common	pidfd_send_signal	sys_pidfd_send_signal
 434	common	pidfd_open		sys_pidfd_open
+440	common	process_madvise		sys_process_madvise
 
 #
 # x32-specific system call numbers start at 512 to avoid cache impact

include/linux/syscalls.h

@@ -501,6 +501,8 @@ asmlinkage long sys_munlock(unsigned long start, size_t len);
 asmlinkage long sys_mlockall(int flags);
 asmlinkage long sys_munlockall(void);
 asmlinkage long sys_madvise(unsigned long start, size_t len, int behavior);
+asmlinkage long sys_process_madvise(int pidfd, const struct iovec __user *vec,
+			size_t vlen, int behavior, unsigned int flags);
 asmlinkage long sys_mincore(unsigned long start, size_t len,
 				unsigned char __user * vec);
 

include/uapi/asm-generic/unistd.h

@@ -736,9 +736,11 @@ __SYSCALL(__NR_statx,     sys_statx)
 __SYSCALL(__NR_pidfd_send_signal, sys_pidfd_send_signal)
 #define __NR_pidfd_open 434
 __SYSCALL(__NR_pidfd_open, sys_pidfd_open)
+#define __NR_process_madvise 440
+__SYSCALL(__NR_process_madvise, sys_process_madvise)
 
 #undef __NR_syscalls
-#define __NR_syscalls 435
+#define __NR_syscalls 441
 
 /*
  * All syscalls below here should go away really,

kernel/sys_ni.c

@@ -202,6 +202,7 @@ cond_syscall(sys_munlockall);
 cond_syscall(sys_mlock2);
 cond_syscall(sys_mincore);
 cond_syscall(sys_madvise);
+cond_syscall(process_madvise);
 cond_syscall(sys_mremap);
 cond_syscall(sys_remap_file_pages);
 cond_syscall(compat_sys_move_pages);

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>
@@ -26,8 +27,7 @@
 #include <linux/swapops.h>
 #include <linux/shmem_fs.h>
 #include <linux/mmu_notifier.h>
-#include <linux/sched/mm.h>
-
+#include <linux/uio.h>
 #include <asm/tlb.h>
 
 #include "internal.h"
@@ -1013,6 +1013,18 @@ 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;
+	}
+}
+
 /*
  * The madvise(2) system call.
  *
@@ -1060,6 +1072,11 @@ madvise_behavior_valid(int behavior)
  *  MADV_DONTDUMP - the application wants to prevent pages in the given range
  *		from being included in its core dump.
  *  MADV_DODUMP - cancel MADV_DONTDUMP: no longer exclude from core dump.
+ *  MADV_COLD - the application is not expected to use this memory soon,
+ *		deactivate pages in this range so that they can be reclaimed
+ *		easily if memory pressure hanppens.
+ *  MADV_PAGEOUT - the application is not expected to use this memory soon,
+ *		page out the pages in this range immediately.
  *
  * return values:
  *  zero    - success
@@ -1193,3 +1210,76 @@ SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
 {
 	return do_madvise(current->mm, start, len_in, behavior);
 }
+
+SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
+		size_t, vlen, int, behavior, unsigned int, flags)
+{
+	ssize_t ret;
+	struct iovec iovstack[UIO_FASTIOV], iovec;
+	struct iovec *iov = iovstack;
+	struct iov_iter iter;
+	struct pid *pid;
+	struct task_struct *task;
+	struct mm_struct *mm;
+	size_t total_len;
+	unsigned int f_flags;
+
+	if (flags != 0) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	ret = import_iovec(READ, vec, vlen, ARRAY_SIZE(iovstack), &iov, &iter);
+	if (ret < 0)
+		goto out;
+
+	pid = pidfd_get_pid(pidfd, &f_flags);
+	if (IS_ERR(pid)) {
+		ret = PTR_ERR(pid);
+		goto free_iov;
+	}
+
+	task = get_pid_task(pid, PIDTYPE_PID);
+	if (!task) {
+		ret = -ESRCH;
+		goto put_pid;
+	}
+
+	if (task->mm != current->mm &&
+	    !process_madvise_behavior_valid(behavior)) {
+		ret = -EINVAL;
+		goto release_task;
+	}
+
+	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;
+	}
+
+	total_len = iov_iter_count(&iter);
+
+	while (iov_iter_count(&iter)) {
+		iovec = iov_iter_iovec(&iter);
+		ret = do_madvise(mm, (unsigned long)iovec.iov_base,
+				 iovec.iov_len, behavior);
+		if (ret < 0)
+			break;
+		iov_iter_advance(&iter, iovec.iov_len);
+	}
+
+	if (ret == 0)
+		ret = total_len - iov_iter_count(&iter);
+
+	mmput(mm);
+	return ret;
+
+release_task:
+	put_task_struct(task);
+put_pid:
+	put_pid(pid);
+free_iov:
+	kfree(iov);
+out:
+	return ret;
+}