[PATCH v5 2/2] selftest: Add MREMAP_DONTUNMAP selftest.

Brian Geffon
2020-02-14T04:10:39Z

Add a few simple self tests for the new flag MREMAP_DONTUNMAP,
they are simple smoke tests which also demonstrate the behavior.

Signed-off-by: Brian Geffon <bgeffon@google.com>
---
tools/testing/selftests/vm/Makefile | 1 +
tools/testing/selftests/vm/mremap_dontunmap.c | 326 ++++++++++++++++++
tools/testing/selftests/vm/run_vmtests | 15 +
3 files changed, 342 insertions(+)
create mode 100644 tools/testing/selftests/vm/mremap_dontunmap.c

diff --git a/tools/testing/selftests/vm/Makefile b/tools/testing/selftests/vm/Makefile
index 9534dc2bc929..4b2b969fc3c7 100644
--- a/tools/testing/selftests/vm/Makefile
+++ b/tools/testing/selftests/vm/Makefile
@@ -12,6 +12,7 @@ TEST_GEN_FILES += map_fixed_noreplace
TEST_GEN_FILES += map_populate
TEST_GEN_FILES += mlock-random-test
TEST_GEN_FILES += mlock2-tests
+TEST_GEN_FILES += mremap_dontunmap
TEST_GEN_FILES += on-fault-limit
TEST_GEN_FILES += thuge-gen
TEST_GEN_FILES += transhuge-stress
diff --git a/tools/testing/selftests/vm/mremap_dontunmap.c b/tools/testing/selftests/vm/mremap_dontunmap.c
new file mode 100644
index 000000000000..de2a861c7c6d
--- /dev/null
+++ b/tools/testing/selftests/vm/mremap_dontunmap.c
@@ -0,0 +1,326 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Tests for mremap w/ MREMAP_DONTUNMAP.
+ *
+ * Copyright 2020, Brian Geffon <bgeffon@google.com>
+ */
+#define _GNU_SOURCE
+#include <sys/mman.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "../kselftest.h"
+
+#ifndef MREMAP_DONTUNMAP
+#define MREMAP_DONTUNMAP 4
+#endif
+
+unsigned long page_size;
+char *page_buffer;
+
+static void dump_maps(void)
+{
+ char cmd[32];
+
+ snprintf(cmd, sizeof(cmd), "cat /proc/%d/maps", getpid());
+ system(cmd);
+}
+
+#define BUG_ON(condition, description) \
+ do { \
+ if (condition) { \
+ fprintf(stderr, "[FAIL]\t%s():%d\t%s:%s\n", __func__, \
+ __LINE__, (description), strerror(errno)); \
+ dump_maps(); \
+ exit(1); \
+ } \
+ } while (0)
+
+// Try a simple operation for to "test" for kernel support this prevents
+// reporting tests as failed when it's run on an older kernel.
+static int kernel_support_for_mremap_dontunmap()
+{
+ int ret = 0;
+ unsigned long num_pages = 1;
+ void *source_mapping = mmap(NULL, num_pages * page_size, PROT_NONE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ BUG_ON(source_mapping == MAP_FAILED, "mmap");
+
+ // This simple remap should only fail if MREMAP_DONTUNMAP isn't
+ // supported.
+ void *dest_mapping =
+ mremap(source_mapping, num_pages * page_size, num_pages * page_size,
+ MREMAP_DONTUNMAP | MREMAP_MAYMOVE, 0);
+ if (dest_mapping == MAP_FAILED) {
+ ret = errno;
+ } else {
+ BUG_ON(munmap(dest_mapping, num_pages * page_size) == -1,
+ "unable to unmap destination mapping");
+ }
+
+ BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
+ "unable to unmap source mapping");
+ return ret;
+}
+
+// This helper will just validate that an entire mapping contains the expected
+// byte.
+static int check_region_contains_byte(void *addr, unsigned long size, char byte)
+{
+ BUG_ON(size & (page_size - 1),
+ "check_region_contains_byte expects page multiples");
+ BUG_ON((unsigned long)addr & (page_size - 1),
+ "check_region_contains_byte expects page alignment");
+
+ memset(page_buffer, byte, page_size);
+
+ unsigned long num_pages = size / page_size;
+ unsigned long i;
+
+ // Compare each page checking that it contains our expected byte.
+ for (i = 0; i < num_pages; ++i) {
+ int ret =
+ memcmp(addr + (i * page_size), page_buffer, page_size);
+ if (ret) {
+ return ret;
+ }
+ }
+
+ return 0;
+}
+
+// this test validates that MREMAP_DONTUNMAP moves the pagetables while leaving
+// the source mapping mapped.
+static void mremap_dontunmap_simple()
+{
+ unsigned long num_pages = 5;
+
+ void *source_mapping =
+ mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ BUG_ON(source_mapping == MAP_FAILED, "mmap");
+
+ memset(source_mapping, 'a', num_pages * page_size);
+
+ // Try to just move the whole mapping anywhere (not fixed).
+ void *dest_mapping =
+ mremap(source_mapping, num_pages * page_size, num_pages * page_size,
+ MREMAP_DONTUNMAP | MREMAP_MAYMOVE, NULL);
+ BUG_ON(dest_mapping == MAP_FAILED, "mremap");
+
+ // Validate that the pages have been moved, we know they were moved if
+ // the dest_mapping contains a's.
+ BUG_ON(check_region_contains_byte
+ (dest_mapping, num_pages * page_size, 'a') != 0,
+ "pages did not migrate");
+ BUG_ON(check_region_contains_byte
+ (source_mapping, num_pages * page_size, 0) != 0,
+ "source should have no ptes");
+
+ BUG_ON(munmap(dest_mapping, num_pages * page_size) == -1,
+ "unable to unmap destination mapping");
+ BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
+ "unable to unmap source mapping");
+}
+
+// This test validates MREMAP_DONTUNMAP will move page tables to a specific
+// destination using MREMAP_FIXED, also while validating that the source
+// remains intact.
+static void mremap_dontunmap_simple_fixed()
+{
+ unsigned long num_pages = 5;
+
+ // Since we want to guarantee that we can remap to a point, we will
+ // create a mapping up front.
+ void *dest_mapping =
+ mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ BUG_ON(dest_mapping == MAP_FAILED, "mmap");
+ memset(dest_mapping, 'X', num_pages * page_size);
+
+ void *source_mapping =
+ mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ BUG_ON(source_mapping == MAP_FAILED, "mmap");
+ memset(source_mapping, 'a', num_pages * page_size);
+
+ void *remapped_mapping =
+ mremap(source_mapping, num_pages * page_size, num_pages * page_size,
+ MREMAP_FIXED | MREMAP_DONTUNMAP | MREMAP_MAYMOVE,
+ dest_mapping);
+ BUG_ON(remapped_mapping == MAP_FAILED, "mremap");
+ BUG_ON(remapped_mapping != dest_mapping,
+ "mremap should have placed the remapped mapping at dest_mapping");
+
+ // The dest mapping will have been unmap by mremap so we expect the Xs
+ // to be gone and replaced with a's.
+ BUG_ON(check_region_contains_byte
+ (dest_mapping, num_pages * page_size, 'a') != 0,
+ "pages did not migrate");
+
+ // And the source mapping will have had its ptes dropped.
+ BUG_ON(check_region_contains_byte
+ (source_mapping, num_pages * page_size, 0) != 0,
+ "source should have no ptes");
+
+ BUG_ON(munmap(dest_mapping, num_pages * page_size) == -1,
+ "unable to unmap destination mapping");
+ BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
+ "unable to unmap source mapping");
+}
+
+// This test validates that we can MREMAP_DONTUNMAP for a portion of an
+// existing mapping.
+static void mremap_dontunmap_partial_mapping()
+{
+ /*
+ * source mapping:
+ * --------------
+ * | aaaaaaaaaa |
+ * --------------
+ * to become:
+ * --------------
+ * | aaaaa00000 |
+ * --------------
+ * With the destination mapping containing 5 pages of As.
+ * ---------
+ * | aaaaa |
+ * ---------
+ */
+ unsigned long num_pages = 10;
+ void *source_mapping =
+ mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ BUG_ON(source_mapping == MAP_FAILED, "mmap");
+ memset(source_mapping, 'a', num_pages * page_size);
+
+ // We will grab the last 5 pages of the source and move them.
+ void *dest_mapping =
+ mremap(source_mapping + (5 * page_size), 5 * page_size,
+ 5 * page_size,
+ MREMAP_DONTUNMAP | MREMAP_MAYMOVE, NULL);
+ BUG_ON(dest_mapping == MAP_FAILED, "mremap");
+
+ // We expect the first 5 pages of the source to contain a's and the
+ // final 5 pages to contain zeros.
+ BUG_ON(check_region_contains_byte(source_mapping, 5 * page_size, 'a') !=
+ 0, "first 5 pages of source should have original pages");
+ BUG_ON(check_region_contains_byte
+ (source_mapping + (5 * page_size), 5 * page_size, 0) != 0,
+ "final 5 pages of source should have no ptes");
+
+ // Finally we expect the destination to have 5 pages worth of a's.
+ BUG_ON(check_region_contains_byte(dest_mapping, 5 * page_size, 'a') !=
+ 0, "dest mapping should contain ptes from the source");
+
+ BUG_ON(munmap(dest_mapping, 5 * page_size) == -1,
+ "unable to unmap destination mapping");
+ BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
+ "unable to unmap source mapping");
+}
+
+// This test validates that we can shrink an existing mapping via the normal
+// mremap behavior along with the MREMAP_DONTUNMAP flag.
+static void mremap_dontunmap_shrink_mapping()
+{
+ /*
+ * We shrink the source by 5 pages while remapping.
+ * source mapping:
+ * --------------
+ * | aaaaaaaaaa |
+ * --------------
+ * to become:
+ * ---------
+ * | 00000 |
+ * ---------
+ * With the destination mapping containing 5 pages of As followed by
+ * the original pages of Xs.
+ * --------------
+ * | aaaaaXXXXX |
+ * --------------
+ */
+
+ unsigned long num_pages = 10;
+
+ // We use MREMAP_FIXED because we don't want the mremap to place the
+ // remapped mapping behind the source, if it did
+ // we wouldn't be able to validate that the mapping was in fact
+ // adjusted.
+ void *dest_mapping =
+ mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ BUG_ON(dest_mapping == MAP_FAILED, "mmap");
+ memset(dest_mapping, 'X', num_pages * page_size);
+
+ void *source_mapping =
+ mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ BUG_ON(source_mapping == MAP_FAILED, "mmap");
+ memset(source_mapping, 'a', num_pages * page_size);
+
+ // We are shrinking the mapping while also using MREMAP_DONTUNMAP
+ void *remapped_mapping =
+ mremap(source_mapping, num_pages * page_size, 5 * page_size,
+ MREMAP_FIXED | MREMAP_DONTUNMAP | MREMAP_MAYMOVE,
+ dest_mapping);
+ BUG_ON(remapped_mapping == MAP_FAILED, "mremap");
+ BUG_ON(remapped_mapping != dest_mapping,
+ "expected mremap to place mapping at dest");
+
+ // The last 5 pages of source should have become unmapped while the
+ // first 5 remain.
+ unsigned char buf[5];
+ int ret = mincore(source_mapping + (5 * page_size), 5 * page_size, buf);
+ BUG_ON((ret != -1 || (ret == -1 && errno != ENOMEM)),
+ "we expect -ENOMEM from mincore.");
+
+ BUG_ON(check_region_contains_byte(source_mapping, 5 * page_size, 0) !=
+ 0, "source should have no ptes");
+ BUG_ON(check_region_contains_byte(dest_mapping, 5 * page_size, 'a') !=
+ 0, "dest mapping should contain ptes from the source");
+
+ // And the second half of the destination should be unchanged.
+ BUG_ON(check_region_contains_byte(dest_mapping + (5 * page_size),
+ 5 * page_size, 'X') != 0,
+ "second half of dest shouldn't be touched");
+
+ // Cleanup
+ BUG_ON(munmap(dest_mapping, num_pages * page_size) == -1,
+ "unable to unmap destination mapping");
+ BUG_ON(munmap(source_mapping, 5 * page_size) == -1,
+ "unable to unmap source mapping");
+}
+
+int main(void)
+{
+ page_size = sysconf(_SC_PAGE_SIZE);
+
+ // test for kernel support for MREMAP_DONTUNMAP skipping the test if
+ // not.
+ if (kernel_support_for_mremap_dontunmap() != 0) {
+ printf("No kernel support for MREMAP_DONTUNMAP\n");
+ return KSFT_SKIP;
+ }
+
+ // Keep a page sized buffer around for when we need it.
+ page_buffer =
+ mmap(NULL, page_size, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ BUG_ON(page_buffer == MAP_FAILED, "unable to mmap a page.");
+
+ mremap_dontunmap_simple();
+ mremap_dontunmap_simple_fixed();
+ mremap_dontunmap_partial_mapping();
+ mremap_dontunmap_shrink_mapping();
+
+ BUG_ON(munmap(page_buffer, page_size) == -1,
+ "unable to unmap page buffer");
+
+ printf("OK\n");
+ return 0;
+}
diff --git a/tools/testing/selftests/vm/run_vmtests b/tools/testing/selftests/vm/run_vmtests
index 951c507a27f7..d380b95c5de5 100755
--- a/tools/testing/selftests/vm/run_vmtests
+++ b/tools/testing/selftests/vm/run_vmtests
@@ -227,4 +227,19 @@ else
exitcode=1
fi

+echo "------------------------------------"
+echo "running MREMAP_DONTUNMAP smoke test"
+echo "------------------------------------"
+./mremap_dontunmap
+ret_val=$?
+
+if [ $ret_val -eq 0 ]; then
+ echo "[PASS]"
+elif [ $ret_val -eq $ksft_skip ]; then
+ echo "[SKIP]"
+ exitcode=$ksft_skip
+else
+ echo "[FAIL]"
+ exitcode=1
+fi
exit $exitcode
--
2.25.0.265.gbab2e86ba0-goog