[PATCH v3 2/4] selftests/mm: virtual_address_range: Unmap chunks after validation

["Thomas Weißschuh" <thomas.weissschuh@linutronix.de>]

For each accessed chunk a PTE is created.
More than 1GiB of PTEs is used in this way.
Remove each PTE after validating a chunk to reduce peak memory usage.

It is important to only unmap memory that previously mmap()ed,
as unmapping other mappings like the stack, heap or executable mappings
will crash the process.
The mappings read from /proc/self/maps and the return values from mmap()
don't allow a simple correlation due to merging and no guaranteed order.
To correlate the pointers and mappings use prctl(PR_SET_VMA_ANON_NAME).
While it introduces a test dependency, other alternatives would
introduce runtime or development overhead.

Fixes: 010409649885 ("selftests/mm: confirm VA exhaustion without reliance on correctness of mmap()")
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
---
 tools/testing/selftests/mm/config                  |  1 +
 tools/testing/selftests/mm/virtual_address_range.c | 33 ++++++++++++++++++++--
 2 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/mm/config b/tools/testing/selftests/mm/config
index 4309916f629e36498efb07eb606b2f0c49ee6211..a28baa536332f3fcfb1b83759b5fbb432ae80178 100644
--- a/tools/testing/selftests/mm/config
+++ b/tools/testing/selftests/mm/config
@@ -7,3 +7,4 @@ CONFIG_TEST_HMM=m
 CONFIG_GUP_TEST=y
 CONFIG_TRANSPARENT_HUGEPAGE=y
 CONFIG_MEM_SOFT_DIRTY=y
+CONFIG_ANON_VMA_NAME=y
diff --git a/tools/testing/selftests/mm/virtual_address_range.c b/tools/testing/selftests/mm/virtual_address_range.c
index ea6ccf49ef4c552f26317c2a40b09bca1a677f8f..386e4e46fa65b98af78dee4bb30144eb2b51f528 100644
--- a/tools/testing/selftests/mm/virtual_address_range.c
+++ b/tools/testing/selftests/mm/virtual_address_range.c
@@ -10,6 +10,7 @@
 #include <string.h>
 #include <unistd.h>
 #include <errno.h>
+#include <sys/prctl.h>
 #include <sys/mman.h>
 #include <sys/time.h>
 #include <fcntl.h>
@@ -82,6 +83,24 @@ static void validate_addr(char *ptr, int high_addr)
 		ksft_exit_fail_msg("Bad address %lx\n", addr);
 }
 
+static void mark_range(char *ptr, size_t size)
+{
+	if (prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, ptr, size, "virtual_address_range") == -1) {
+		if (errno == EINVAL) {
+			/* Depends on CONFIG_ANON_VMA_NAME */
+			ksft_test_result_skip("prctl(PR_SET_VMA_ANON_NAME) not supported\n");
+			ksft_finished();
+		} else {
+			ksft_exit_fail_perror("prctl(PR_SET_VMA_ANON_NAME) failed\n");
+		}
+	}
+}
+
+static int is_marked_vma(const char *vma_name)
+{
+	return vma_name && !strcmp(vma_name, "[anon:virtual_address_range]\n");
+}
+
 static int validate_lower_address_hint(void)
 {
 	char *ptr;
@@ -116,12 +135,17 @@ static int validate_complete_va_space(void)
 
 	prev_end_addr = 0;
 	while (fgets(line, sizeof(line), file)) {
+		const char *vma_name = NULL;
+		int vma_name_start = 0;
 		unsigned long hop;
 
-		if (sscanf(line, "%lx-%lx %s[rwxp-]",
-			   &start_addr, &end_addr, prot) != 3)
+		if (sscanf(line, "%lx-%lx %4s %*s %*s %*s %n",
+			   &start_addr, &end_addr, prot, &vma_name_start) != 3)
 			ksft_exit_fail_msg("cannot parse /proc/self/maps\n");
 
+		if (vma_name_start)
+			vma_name = line + vma_name_start;
+
 		/* end of userspace mappings; ignore vsyscall mapping */
 		if (start_addr & (1UL << 63))
 			return 0;
@@ -149,6 +173,9 @@ static int validate_complete_va_space(void)
 				return 1;
 			lseek(fd, 0, SEEK_SET);
 
+			if (is_marked_vma(vma_name))
+				munmap((char *)(start_addr + hop), MAP_CHUNK_SIZE);
+
 			hop += MAP_CHUNK_SIZE;
 		}
 	}
@@ -175,6 +202,7 @@ int main(int argc, char *argv[])
 			break;
 		}
 
+		mark_range(ptr[i], MAP_CHUNK_SIZE);
 		validate_addr(ptr[i], 0);
 	}
 	lchunks = i;
@@ -192,6 +220,7 @@ int main(int argc, char *argv[])
 		if (hptr[i] == MAP_FAILED)
 			break;
 
+		mark_range(ptr[i], MAP_CHUNK_SIZE);
 		validate_addr(hptr[i], 1);
 	}
 	hchunks = i;

-- 
2.47.1