selftest: add simple test for soft-dirty bit

It creates a mapping of 3 pages and checks that reads, writes and
clear-refs result in present and soft-dirt bits reported from pagemap2
set as expected.

[akpm@linux-foundation.org: alphasort the Makefile TARGETS to reduce rejects]
Signed-off-by: NPavel Emelyanov <xemul@parallels.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

tools/testing/selftests/Makefile

 TARGETS = breakpoints
+TARGETS += cpu-hotplug
+TARGETS += efivarfs
 TARGETS += kcmp
+TARGETS += memory-hotplug
 TARGETS += mqueue
+TARGETS += soft-dirty
 TARGETS += vm
-TARGETS += cpu-hotplug
-TARGETS += memory-hotplug
-TARGETS += efivarfs
 
 all:
 	for TARGET in $(TARGETS); do \

tools/testing/selftests/soft-dirty/Makefile

+CFLAGS += -iquote../../../../include/uapi -Wall
+soft-dirty: soft-dirty.c
+
+all: soft-dirty
+
+clean:
+	rm -f soft-dirty
+
+run_tests: all
+	@./soft-dirty || echo "soft-dirty selftests: [FAIL]"

tools/testing/selftests/soft-dirty/soft-dirty.c

+#include <stdlib.h>
+#include <stdio.h>
+#include <sys/mman.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/types.h>
+
+typedef unsigned long long u64;
+
+#define PME_PRESENT	(1ULL << 63)
+#define PME_SOFT_DIRTY	(1Ull << 55)
+
+#define PAGES_TO_TEST	3
+#ifndef PAGE_SIZE
+#define PAGE_SIZE	4096
+#endif
+
+static void get_pagemap2(char *mem, u64 *map)
+{
+	int fd;
+
+	fd = open("/proc/self/pagemap2", O_RDONLY);
+	if (fd < 0) {
+		perror("Can't open pagemap2");
+		exit(1);
+	}
+
+	lseek(fd, (unsigned long)mem / PAGE_SIZE * sizeof(u64), SEEK_SET);
+	read(fd, map, sizeof(u64) * PAGES_TO_TEST);
+	close(fd);
+}
+
+static inline char map_p(u64 map)
+{
+	return map & PME_PRESENT ? 'p' : '-';
+}
+
+static inline char map_sd(u64 map)
+{
+	return map & PME_SOFT_DIRTY ? 'd' : '-';
+}
+
+static int check_pte(int step, int page, u64 *map, u64 want)
+{
+	if ((map[page] & want) != want) {
+		printf("Step %d Page %d has %c%c, want %c%c\n",
+				step, page,
+				map_p(map[page]), map_sd(map[page]),
+				map_p(want), map_sd(want));
+		return 1;
+	}
+
+	return 0;
+}
+
+static void clear_refs(void)
+{
+	int fd;
+	char *v = "4";
+
+	fd = open("/proc/self/clear_refs", O_WRONLY);
+	if (write(fd, v, 3) < 3) {
+		perror("Can't clear soft-dirty bit");
+		exit(1);
+	}
+	close(fd);
+}
+
+int main(void)
+{
+	char *mem, x;
+	u64 map[PAGES_TO_TEST];
+
+	mem = mmap(NULL, PAGES_TO_TEST * PAGE_SIZE,
+			PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, 0, 0);
+
+	x = mem[0];
+	mem[2 * PAGE_SIZE] = 'c';
+	get_pagemap2(mem, map);
+
+	if (check_pte(1, 0, map, PME_PRESENT))
+		return 1;
+	if (check_pte(1, 1, map, 0))
+		return 1;
+	if (check_pte(1, 2, map, PME_PRESENT | PME_SOFT_DIRTY))
+		return 1;
+
+	clear_refs();
+	get_pagemap2(mem, map);
+
+	if (check_pte(2, 0, map, PME_PRESENT))
+		return 1;
+	if (check_pte(2, 1, map, 0))
+		return 1;
+	if (check_pte(2, 2, map, PME_PRESENT))
+		return 1;
+
+	mem[0] = 'a';
+	mem[PAGE_SIZE] = 'b';
+	x = mem[2 * PAGE_SIZE];
+	get_pagemap2(mem, map);
+
+	if (check_pte(3, 0, map, PME_PRESENT | PME_SOFT_DIRTY))
+		return 1;
+	if (check_pte(3, 1, map, PME_PRESENT | PME_SOFT_DIRTY))
+		return 1;
+	if (check_pte(3, 2, map, PME_PRESENT))
+		return 1;
+
+	(void)x; /* gcc warn */
+
+	printf("PASS\n");
+	return 0;
+}