restore: Fetch mmap_minimal_address runtime

We assume that mmap_minimal_address with non-default
setting is not widespread but it's not true. Instead
lets fetch this setting runtime.

travis-ci: success for Fetch mmap_minimal_address and drop MAP_ANON
Signed-off-by: Cyrill Gorcunov <gorcunov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

criu/cr-restore.c

@@ -1969,7 +1969,7 @@ static long restorer_get_vma_hint(struct list_head *tgt_vma_list,
 
 	end_vma.e = &end_e;
 	end_e.start = end_e.end = kdat.task_size;
-	prev_vma_end = PAGE_SIZE * 0x10; /* CONFIG_LSM_MMAP_MIN_ADDR=65536 */
+	prev_vma_end = kdat.mmap_min_addr;
 
 	s_vma = list_first_entry(self_vma_list, struct vma_area, list);
 	t_vma = list_first_entry(tgt_vma_list, struct vma_area, list);

criu/include/kerndat.h

@@ -35,6 +35,7 @@ struct kerndat_s {
 	bool has_loginuid;
 	enum pagemap_func pmap;
 	unsigned int has_xtlocks;
+	unsigned long mmap_min_addr;
 };
 
 extern struct kerndat_s kdat;

criu/kerndat.c

@@ -8,6 +8,8 @@
 #include <errno.h>
 #include <sys/syscall.h>
 #include <sys/sysmacros.h>
+#include <sys/sysmacros.h>
+#include <stdint.h>
 
 #include "int.h"
 #include "log.h"
@@ -106,6 +108,39 @@ static int parse_self_maps(unsigned long vm_start, dev_t *device)
 	return -1;
 }
 
+static void kerndat_mmap_min_addr(void)
+{
+	/* From kernel's default CONFIG_LSM_MMAP_MIN_ADDR */
+	static const unsigned long default_mmap_min_addr = 65536;
+	uint64_t value;
+
+	struct sysctl_req req[] = {
+		{
+			.name	= "vm/mmap_min_addr",
+			.arg	= &value,
+			.type	= CTL_U64,
+		},
+	};
+
+	if (sysctl_op(req, ARRAY_SIZE(req), CTL_READ, 0)) {
+		pr_warn("Can't fetch %s value, use default %#lx\n",
+			req[0].name, (unsigned long)default_mmap_min_addr);
+		kdat.mmap_min_addr = default_mmap_min_addr;
+		return;
+	}
+
+	if (value < default_mmap_min_addr) {
+		pr_debug("Adjust mmap_min_addr %#lx -> %#lx\n",
+			 (unsigned long)value,
+			 (unsigned long)default_mmap_min_addr);
+		kdat.mmap_min_addr = default_mmap_min_addr;
+	} else
+		kdat.mmap_min_addr = value;
+
+	pr_debug("Found mmap_min_addr %#lx\n",
+		 (unsigned long)kdat.mmap_min_addr);
+}
+
 static int kerndat_get_shmemdev(void)
 {
 	void *map;
@@ -483,6 +518,7 @@ int kerndat_init(void)
 		ret = kerndat_tcp_repair_window();
 
 	kerndat_lsm();
+	kerndat_mmap_min_addr();
 
 	return ret;
 }
@@ -514,6 +550,7 @@ int kerndat_init_rst(void)
 		ret = kerndat_tcp_repair_window();
 
 	kerndat_lsm();
+	kerndat_mmap_min_addr();
 
 	return ret;
 }