[PATCH V3] MIPS: Add get_thread_area syscall

[Guoyun Sun <sunguoyun@loongson.cn>]

CRIU(https://criu.org/) tools will dump TLS(Thread Local Storage) by
get_thread_area during checkpoint and restore TLS by set_thread_area during
restore. without this syscall, criu restore will fail on MIPS platform
because a variable with GCC __thread will be invalid.

The following function will be called when criu restore

static inline void restore_tls(tls_t *ptls) {
        asm volatile(
                     "move $4, %0                                   \n"
                     "li $2,  "__stringify(__NR_set_thread_area)"  \n"
                     "syscall                                       \n"
                     :
                     : "r"(*ptls)
                     : "$4","$2","memory");

the *ptls can be obtained by get_thread_area on MIPS platform when criu
checkpoint. just like this:

static inline void arch_get_tls(tls_t *ptls)
{
	asm volatile(
		     "move $4, %0				    \n"
		     "li $2,  "__stringify(__NR_get_thread_area)"  \n"
		     "syscall					    \n"
		     :
		     : "r"(ptls)
		     : "$4","$2","memory");

}

Signed-off-by: Guoyun Sun <sunguoyun@loongson.cn>
---
 arch/mips/kernel/syscall.c                | 11 +++++++++++
 arch/mips/kernel/syscalls/syscall_n32.tbl |  2 ++
 arch/mips/kernel/syscalls/syscall_n64.tbl |  2 ++
 arch/mips/kernel/syscalls/syscall_o32.tbl |  2 ++
 4 files changed, 17 insertions(+)

diff --git a/arch/mips/kernel/syscall.c b/arch/mips/kernel/syscall.c
index c333e57..7ac78bf 100644
--- a/arch/mips/kernel/syscall.c
+++ b/arch/mips/kernel/syscall.c
@@ -27,6 +27,7 @@
 #include <linux/slab.h>
 #include <linux/elf.h>
 #include <linux/sched/task_stack.h>
+#include <linux/compat.h>
 
 #include <asm/asm.h>
 #include <asm/asm-eva.h>
@@ -94,6 +95,16 @@ SYSCALL_DEFINE1(set_thread_area, unsigned long, addr)
 	return 0;
 }
 
+SYSCALL_DEFINE1(get_thread_area, unsigned long __user *, u_info)
+{
+	struct thread_info *ti = task_thread_info(current);
+
+	if (in_compat_syscall())
+		return put_user(ti->tp_value, (__u32 *)u_info);
+
+	return put_user(ti->tp_value, u_info);
+}
+
 static inline int mips_atomic_set(unsigned long addr, unsigned long new)
 {
 	unsigned long old, tmp;
diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl
index e7c5ab3..3aa4858 100644
--- a/arch/mips/kernel/syscalls/syscall_n32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n32.tbl
@@ -341,6 +341,8 @@
 330	n32	statx				sys_statx
 331	n32	rseq				sys_rseq
 332	n32	io_pgetevents			compat_sys_io_pgetevents
+333	n32	get_thread_area			sys_get_thread_area
+
 # 333 through 402 are unassigned to sync up with generic numbers
 403	n32	clock_gettime64			sys_clock_gettime
 404	n32	clock_settime64			sys_clock_settime
diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl
index 13cd665..14b6796 100644
--- a/arch/mips/kernel/syscalls/syscall_n64.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n64.tbl
@@ -337,6 +337,8 @@
 326	n64	statx				sys_statx
 327	n64	rseq				sys_rseq
 328	n64	io_pgetevents			sys_io_pgetevents
+329	n64	get_thread_area			sys_get_thread_area
+
 # 329 through 423 are reserved to sync up with other architectures
 424	n64	pidfd_send_signal		sys_pidfd_send_signal
 425	n64	io_uring_setup			sys_io_uring_setup
diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl
index 353539e..bb4e050 100644
--- a/arch/mips/kernel/syscalls/syscall_o32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_o32.tbl
@@ -380,6 +380,8 @@
 366	o32	statx				sys_statx
 367	o32	rseq				sys_rseq
 368	o32	io_pgetevents			sys_io_pgetevents_time32	compat_sys_io_pgetevents
+369	o32	get_thread_area			sys_get_thread_area
+
 # room for arch specific calls
 393	o32	semget				sys_semget
 394	o32	semctl				sys_semctl			compat_sys_semctl
-- 
2.1.0