[dpdk-dev] [PATCH 1/2] memalloc: do not leave unmapped holes in EAL virtual memory area

[Dariusz Stojaczyk]

EAL reserves a huge area in virtual address space
to provide virtual address contiguity for e.g.
future memory extensions (memory hotplug). During
memory hotplug, if the hugepage mmap succeeds but
doesn't suffice EAL's requiriments, the EAL would
unmap this mapping straight away, leaving a hole in
its virtual memory area and making it available
to everyone. As EAL still thinks it owns the entire
region, it may try to mmap it later with MAP_FIXED,
possibly overriding a user's mapping that was made
in the meantime.

This patch ensures each hole is mapped back by EAL,
so that it won't be available to anyone else.

Changes from v1:
 * checkpatch fixes

Signed-off-by: Dariusz Stojaczyk <dariuszx.stojaczyk at intel.com>
---
 lib/librte_eal/linuxapp/eal/eal_memalloc.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/lib/librte_eal/linuxapp/eal/eal_memalloc.c b/lib/librte_eal/linuxapp/eal/eal_memalloc.c
index 8c11f98..2ab3d34 100644
--- a/lib/librte_eal/linuxapp/eal/eal_memalloc.c
+++ b/lib/librte_eal/linuxapp/eal/eal_memalloc.c
@@ -39,6 +39,7 @@
 #include "eal_filesystem.h"
 #include "eal_internal_cfg.h"
 #include "eal_memalloc.h"
+#include "eal_private.h"
 
 /*
  * not all kernel version support fallocate on hugetlbfs, so fall back to
@@ -490,6 +491,8 @@ alloc_seg(struct rte_memseg *ms, void *addr, int socket_id,
 	int ret = 0;
 	int fd;
 	size_t alloc_sz;
+	int flags;
+	void *new_addr;
 
 	/* takes out a read lock on segment or segment list */
 	fd = get_seg_fd(path, sizeof(path), hi, list_idx, seg_idx);
@@ -585,6 +588,20 @@ alloc_seg(struct rte_memseg *ms, void *addr, int socket_id,
 
 mapped:
 	munmap(addr, alloc_sz);
+	flags = MAP_FIXED;
+#ifdef RTE_ARCH_PPC_64
+	flags |= MAP_HUGETLB;
+#endif
+	new_addr = eal_get_virtual_area(addr, &alloc_sz, alloc_sz, 0, flags);
+	if (new_addr != addr) {
+		if (new_addr != NULL)
+			munmap(new_addr, alloc_sz);
+		/* we're leaving a hole in our virtual address space. if
+		 * somebody else maps this hole now, we could accidentally
+		 * override it in the future.
+		 */
+		rte_panic("can't mmap holes in our virtual address space");
+	}
 resized:
 	if (internal_config.single_file_segments) {
 		resize_hugefile(fd, path, list_idx, seg_idx, map_offset,
-- 
2.7.4