[CRIU] [RFC PATCH 07/12] lazy-pages: add handling of UFFD_EVENT_REMAP

[Mike Rapoport]

When the restored process calls mremap(), we will see #PF's on the new
addresses and we have to create a correspondence between the addresses
found in the dump and the actual addresses the process uses. If the
mremap() call causes the mapping to grow, the additional part will receive
zero pages, as expected.

FIXME: is the mapping shrinks, we will try to fill the dropped part and
lazy-pages daemon will fail. It should be possible to track VMA changes in
the lazy-pages daemon, but simpler, and, apparently, more correct would be
to add UFFD_EVENT_MUNMAP to the kernel.

Signed-off-by: Mike Rapoport <rppt at linux.vnet.ibm.com>
---
 criu/uffd.c | 47 ++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 46 insertions(+), 1 deletion(-)

diff --git a/criu/uffd.c b/criu/uffd.c
index 3bc7bc1..8bf4a14 100644
--- a/criu/uffd.c
+++ b/criu/uffd.c
@@ -53,7 +53,12 @@ struct lazy_iovec {
 	unsigned long len;
 };
 
-struct lazy_pages_info;
+struct lazy_remap {
+	struct list_head l;
+	unsigned long from;
+	unsigned long to;
+	unsigned long len;
+};
 
 struct pf_info {
 	unsigned long addr;
@@ -65,6 +70,7 @@ struct lazy_pages_info {
 
 	struct list_head iovs;
 	struct list_head pfs;
+	struct list_head remaps;
 
 	struct page_read pr;
 
@@ -92,6 +98,7 @@ static struct lazy_pages_info *lpi_init(void)
 	memset(lpi, 0, sizeof(*lpi));
 	INIT_LIST_HEAD(&lpi->iovs);
 	INIT_LIST_HEAD(&lpi->pfs);
+	INIT_LIST_HEAD(&lpi->remaps);
 	INIT_LIST_HEAD(&lpi->l);
 	lpi->lpfd.revent = handle_uffd_event;
 
@@ -101,12 +108,15 @@ static struct lazy_pages_info *lpi_init(void)
 static void lpi_fini(struct lazy_pages_info *lpi)
 {
 	struct lazy_iovec *p, *n;
+	struct lazy_remap *p1, *n1;
 
 	if (!lpi)
 		return;
 	free(lpi->buf);
 	list_for_each_entry_safe(p, n, &lpi->iovs, l)
 		xfree(p);
+	list_for_each_entry_safe(p1, n1, &lpi->remaps, l)
+		xfree(p1);
 	if (lpi->lpfd.fd > 0)
 		close(lpi->lpfd.fd);
 	if (lpi->pr.close)
@@ -515,9 +525,17 @@ out:
 static int uffd_copy(struct lazy_pages_info *lpi, __u64 address, int nr_pages)
 {
 	struct uffdio_copy uffdio_copy;
+	struct lazy_remap *r;
 	unsigned long len = nr_pages * page_size();
 	int rc;
 
+	list_for_each_entry(r, &lpi->remaps, l) {
+		if (address >= r->from && address < r->from + r->len) {
+			address += (r->to - r->from);
+			break;
+		}
+	}
+
 	uffdio_copy.dst = address;
 	uffdio_copy.src = (unsigned long)lpi->buf;
 	uffdio_copy.len = len;
@@ -670,9 +688,27 @@ static int handle_madv_dontneed(struct lazy_pages_info *lpi,
 	return 0;
 }
 
+static int handle_remap(struct lazy_pages_info *lpi, struct uffd_msg *msg)
+{
+	struct lazy_remap *remap;
+
+	remap = xmalloc(sizeof(*remap));
+	if (!remap)
+		return -1;
+
+	INIT_LIST_HEAD(&remap->l);
+	remap->from = msg->arg.remap.from;
+	remap->to = msg->arg.remap.to;
+	remap->len = msg->arg.remap.len;
+	list_add_tail(&remap->l, &lpi->remaps);
+
+	return 0;
+}
+
 static int handle_page_fault(struct lazy_pages_info *lpi, struct uffd_msg *msg)
 {
 	struct pf_info *pf;
+	struct lazy_remap *r;
 	__u64 address;
 	int ret;
 
@@ -695,6 +731,13 @@ static int handle_page_fault(struct lazy_pages_info *lpi, struct uffd_msg *msg)
 	}
 #endif
 
+	list_for_each_entry(r, &lpi->remaps, l) {
+		if (address >= r->to && address < r->to + r->len) {
+			address -= (r->to - r->from);
+			break;
+		}
+	}
+
 	list_for_each_entry(pf, &lpi->pfs, l)
 		if (pf->addr == address)
 			return 0;
@@ -742,6 +785,8 @@ static int handle_uffd_event(struct epoll_rfd *lpfd)
 		return handle_page_fault(lpi, &msg);
 	case UFFD_EVENT_MADVDONTNEED:
 		return handle_madv_dontneed(lpi, &msg);
+	case UFFD_EVENT_REMAP:
+		return handle_remap(lpi, &msg);
 	default:
 		pr_err("unexpected uffd event %u\n", msg.event);
 		return -1;
-- 
1.9.1