soft-dirty: Check that kernel reports soft-dirty bits

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

cr-check.c

@@ -25,6 +25,7 @@
 #include "mount.h"
 #include "tty.h"
 #include "ptrace.h"
+#include "kerndat.h"
 
 static int check_tty(void)
 {
@@ -486,6 +487,16 @@ int check_ptrace_peeksiginfo()
 	return ret;
 }
 
+static int check_mem_dirty_track(void)
+{
+	if (kerndat_get_dirty_track() < 0)
+		return -1;
+
+	if (!kerndat_has_dirty_track)
+		pr_info("Dirty tracking is OFF. Memory snapshot will not work.\n");
+	return 0;
+}
+
 int cr_check(void)
 {
 	int ret = 0;
@@ -513,6 +524,7 @@ int cr_check(void)
 	ret |= check_ipc();
 	ret |= check_sigqueuinfo();
 	ret |= check_ptrace_peeksiginfo();
+	ret |= check_mem_dirty_track();
 
 	if (!ret)
 		pr_msg("Looks good.\n");

include/kerndat.h

@@ -1,11 +1,16 @@
 #ifndef __CR_KERNDAT_H__
 #define __CR_KERNDAT_H__
+
+#include "asm/types.h"
+
 /*
  * kerndat stands for "kernel data" and is a collection
  * of run-time information about current kernel
  */
 
 int kerndat_init(void);
+int kerndat_get_dirty_track(void);
 
 extern dev_t kerndat_shmem_dev;
+extern bool kerndat_has_dirty_track;
 #endif

kerndat.c

@@ -1,3 +1,5 @@
+#include <unistd.h>
+#include <fcntl.h>
 #include <stdio.h>
 #include <sys/stat.h>
 #include <sys/types.h>
@@ -42,11 +44,57 @@ static int kerndat_get_shmemdev(void)
 	return 0;
 }
 
+/*
+ * Check whether pagemap2 reports soft dirty bit. Kernel has
+ * this functionality under CONFIG_MEM_SOFT_DIRTY option.
+ */
+
+#define PME_SOFT_DIRTY	(1Ull << 55)
+
+bool kerndat_has_dirty_track = false;
+
+int kerndat_get_dirty_track(void)
+{
+	char *map;
+	int pm2;
+	u64 pmap = 0;
+
+	map = mmap(NULL, PAGE_SIZE, PROT_READ | PROT_WRITE,
+			MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
+	if (map == MAP_FAILED) {
+		pr_perror("Can't mmap piggie2");
+		return -1;
+	}
+
+	map[0] = '\0';
+
+	pm2 = open("/proc/self/pagemap2", O_RDONLY);
+	if (pm2 < 0) {
+		pr_perror("Can't open pagemap2 file");
+		return -1;
+	}
+
+	lseek(pm2, (unsigned long)map / PAGE_SIZE * sizeof(u64), SEEK_SET);
+	read(pm2, &pmap, sizeof(pmap));
+	close(pm2);
+	munmap(map, PAGE_SIZE);
+
+	if (pmap & PME_SOFT_DIRTY) {
+		pr_info("Dirty track supported on kernel\n");
+		kerndat_has_dirty_track = true;
+	} else
+		pr_err("Dirty tracking support is OFF\n");
+
+	return 0;
+}
+
 int kerndat_init(void)
 {
 	int ret;
 
 	ret = kerndat_get_shmemdev();
+	if (!ret)
+		ret = kerndat_get_dirty_track();
 
 	return ret;
 }

mem.c

@@ -10,6 +10,7 @@
 #include "page-pipe.h"
 #include "page-xfer.h"
 #include "log.h"
+#include "kerndat.h"
 
 #include "protobuf.h"
 #include "protobuf/pagemap.pb-c.h"
@@ -62,6 +63,12 @@ static struct mem_snap_ctx *mem_snap_init(struct parasite_ctl *ctl)
 	if (!opts.mem_snapshot)
 		return NULL;
 
+	if (!kerndat_has_dirty_track) {
+		pr_err("Kernel doesn't support dirty tracking. "
+				"No snapshot available.\n");
+		return ERR_PTR(-1);
+	}
+
 	p_fd = get_service_fd(PARENT_FD_OFF);
 	if (p_fd < 0) {
 		pr_debug("Will do full memory dump\n");