[CRIU] [PATCH cr 09/16] restorer: remap private vmas to correct places

[Andrey Vagin]

All private vmas are placed in a premmapped region and
they are sorted by start addresses, so they should be shifted apart.

Here is one more problem with overlapped temporary and target regions,
mremap could not remap such cases directly, so for such cases a vma is
remapped away and then remapped on a target place.

Signed-off-by: Andrey Vagin <avagin at openvz.org>
---
 cr-restore.c       |    1 +
 include/restorer.h |    1 +
 restorer.c         |   94 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 96 insertions(+), 0 deletions(-)

diff --git a/cr-restore.c b/cr-restore.c
index 1f22df0..4e27c06 100644
--- a/cr-restore.c
+++ b/cr-restore.c
@@ -1580,6 +1580,7 @@ static int sigreturn_restore(pid_t pid, CoreEntry *core, struct list_head *tgt_v
 
 	mem += self_vmas_len;
 	task_args->tgt_vmas = vma_list_remap(mem, vmas_len, tgt_vmas);
+	task_args->nr_vmas = nr_vmas;
 	task_args->premmapped_addr = (unsigned long) premmapped_addr;
 	task_args->premmapped_len = premmapped_len;
 	if (!task_args->tgt_vmas)
diff --git a/include/restorer.h b/include/restorer.h
index aed8ea2..de73b3c 100644
--- a/include/restorer.h
+++ b/include/restorer.h
@@ -89,6 +89,7 @@ struct task_restore_core_args {
 	struct task_entries		*task_entries;
 	VmaEntry			*self_vmas;
 	VmaEntry			*tgt_vmas;
+	unsigned int			nr_vmas;
 	unsigned long			premmapped_addr;
 	unsigned long			premmapped_len;
 	rt_sigaction_t			sigchld_act;
diff --git a/restorer.c b/restorer.c
index 1a5cff0..2b54042 100644
--- a/restorer.c
+++ b/restorer.c
@@ -289,6 +289,64 @@ static void rst_tcp_socks_all(int *arr, int size)
 	sys_munmap(arr, size);
 }
 
+static int vma_remap(unsigned long src, unsigned long dst, unsigned long len)
+{
+	unsigned long guard = 0, tmp;
+
+	pr_info("Remap %lx->%lx len %lx\n", src, dst, len);
+
+	if (src - dst < len)
+		guard = dst;
+	else if (dst - src < len)
+		guard = dst + len - PAGE_SIZE;
+
+	if (src == dst)
+		return 0;
+
+	if (guard == 0) {
+		tmp = sys_mremap(src, len, len, MREMAP_MAYMOVE | MREMAP_FIXED, dst);
+		if (tmp != dst) {
+			pr_err("Unable to remap %lx -> %lx\n", src, dst);
+			return -1;
+		}
+	} else {
+		/* Regions are overlapped */
+		unsigned long addr;
+
+		/* Prevent overlapping with a temporary place */
+		tmp = sys_mmap((void *) guard, PAGE_SIZE, PROT_NONE,
+					MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
+		if (tmp != guard) {
+			pr_err("Unable to map a guard page %lx (%lx)\n", guard, tmp);
+			return -1;
+		}
+
+		/* Choose a temporary place */
+		addr = sys_mmap(NULL, len, PROT_NONE,
+					MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
+		if (addr == (unsigned long) MAP_FAILED) {
+			pr_err("Unable to reserve memory (%lx)\n", addr);
+			return -1;
+		}
+
+		tmp = sys_mremap(src, len, len,
+					MREMAP_MAYMOVE | MREMAP_FIXED, addr);
+		if (tmp != addr) {
+			pr_err("Unable to remap %lx -> %lx (%lx)\n", src, addr, tmp);
+			return -1;
+		}
+
+		tmp = sys_mremap(addr, len, len,
+					MREMAP_MAYMOVE | MREMAP_FIXED, dst);
+		if (tmp != dst) {
+			pr_err("Unable to remap %lx -> %lx (%lx)\n", addr, dst, tmp);
+			return -1;
+		}
+	}
+
+	return 0;
+}
+
 /*
  * The main routine to restore task via sigreturn.
  * This one is very special, we never return there
@@ -334,6 +392,39 @@ long __export_restore_task(struct task_restore_core_args *args)
 	sys_munmap(args->self_vmas,
 			((void *)(vma_entry + 1) - ((void *)args->self_vmas)));
 
+	/* Shift private vma-s to the left */
+	for (vma_entry = args->tgt_vmas; vma_entry->start != 0; vma_entry++) {
+		if (!vma_entry_is(vma_entry, VMA_AREA_REGULAR))
+			continue;
+
+		if (!vma_priv(vma_entry))
+			continue;
+
+		if (vma_entry->start > vma_entry->shmid)
+			break;
+
+		if (vma_remap(vma_premmaped_start(vma_entry),
+				vma_entry->start, vma_entry_len(vma_entry)))
+			goto core_restore_end;
+	}
+
+	/* Shift private vma-s to the right */
+	for (vma_entry = args->tgt_vmas + args->nr_vmas -1;
+				vma_entry >= args->tgt_vmas; vma_entry--) {
+		if (!vma_entry_is(vma_entry, VMA_AREA_REGULAR))
+			continue;
+
+		if (!vma_priv(vma_entry))
+			continue;
+
+		if (vma_entry->start < vma_entry->shmid)
+			break;
+
+		if (vma_remap(vma_premmaped_start(vma_entry),
+				vma_entry->start, vma_entry_len(vma_entry)))
+			goto core_restore_end;
+	}
+
 	/*
 	 * OK, lets try to map new one.
 	 */
@@ -341,6 +432,9 @@ long __export_restore_task(struct task_restore_core_args *args)
 		if (!vma_entry_is(vma_entry, VMA_AREA_REGULAR))
 			continue;
 
+		if (vma_priv(vma_entry))
+			continue;
+
 		va = restore_mapping(vma_entry);
 
 		if (va != vma_entry->start) {
-- 
1.7.1