[CRIU] [PATCH 8/8] lazy-pages: don't try to uffd_copy to removed memory regions

[Mike Rapoport]

It is possible that when pages request from the remove source arrive, part
of the memory range covered by the request would be already gone because of
madvise(MADV_DONTNEED), mremap() etc.
Ensure we are not trying to uffd_copy more than we are allowed.

Signed-off-by: Mike Rapoport <rppt at linux.vnet.ibm.com>
---
 criu/uffd.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/criu/uffd.c b/criu/uffd.c
index 4022fc5..7f6a59c 100644
--- a/criu/uffd.c
+++ b/criu/uffd.c
@@ -839,6 +839,7 @@ static int uffd_io_complete(struct page_read *pr, unsigned long img_addr, int nr
 {
 	struct lazy_pages_info *lpi;
 	unsigned long addr = 0;
+	int req_pages;
 	struct lazy_iov *req;
 
 	lpi = container_of(pr, struct lazy_pages_info, pr);
@@ -864,6 +865,14 @@ static int uffd_io_complete(struct page_read *pr, unsigned long img_addr, int nr
 	if (!addr)
 		return 0;
 
+	/*
+	 * by the time we get the pages from the remote source, parts
+	 * of the request may already be gone because of
+	 * UFFD_EVENT_{REMAP,REMOVE,UNMAP}
+	 */
+	req_pages = (req->end - req->start) / PAGE_SIZE;
+	nr = min(nr, req_pages);
+
 	return uffd_copy(lpi, addr, nr);
 }
 
-- 
2.7.4