lazy-pages: update drop_lazy_iovs to handle addresses outside IOVs

Currently drop_lazy_iovs presumes that the range that should be dropped
starts inside an IOV. This works fine with page faults and background pages
but will fail for mapping changes.

travis-ci: success for lazy-pages: add non-#PF events handling (rev2)
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

criu/uffd.c

@@ -340,12 +340,17 @@ static int drop_lazy_iovs(struct lazy_pages_info *lpi, unsigned long addr,
 		unsigned long start = iov->base;
 		unsigned long end = start + iov->len;
 
-		if (len <= 0)
+		if (len <= 0 || addr + len < start)
 			break;
 
-		if (addr < start || addr >= end)
+		if (addr >= end)
 			continue;
 
+		if (addr < start) {
+			len -= (start - addr);
+			addr = start;
+		}
+
 		/*
 		 * The range completely fits into the current IOV.
 		 * If addr equals iov_base we just "drop" the