// SPDX-License-Identifier: GPL-2.0
/*
* Tests for mremap w/ MREMAP_DONTUNMAP.
*
* Copyright 2020, Brian Geffon <[email protected]>
*/
#define _GNU_SOURCE
#include <sys/mman.h>
#include <linux/mman.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "../kselftest.h"
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) { \
dump_maps(); \
ksft_exit_fail_msg("[FAIL]\t%s:%d\t%s:%s\n", \
__func__, __LINE__, (description), \
strerror(errno)); \
} \
} 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");
ksft_test_result_pass("%s\n", __func__);
}
// This test validates that MREMAP_DONTUNMAP on a shared mapping works as expected.
static void mremap_dontunmap_simple_shmem()
{
unsigned long num_pages = 5;
int mem_fd = memfd_create("memfd", MFD_CLOEXEC);
BUG_ON(mem_fd < 0, "memfd_create");
BUG_ON(ftruncate(mem_fd, num_pages * page_size) < 0,
"ftruncate");
void *source_mapping =
mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
MAP_FILE | MAP_SHARED, mem_fd, 0);
BUG_ON(source_mapping == MAP_FAILED, "mmap");
BUG_ON(close(mem_fd) < 0, "close");
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);
if (dest_mapping == MAP_FAILED && errno == EINVAL) {
// Old kernel which doesn't support MREMAP_DONTUNMAP on shmem.
BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
"unable to unmap source mapping");
return;
}
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");
// Because the region is backed by shmem, we will actually see the same
// memory at the source location still.
BUG_ON(check_region_contains_byte
(source_mapping, num_pages * page_size, 'a') != 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");
ksft_test_result_pass("%s\n", __func__);
}
// 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");
ksft_test_result_pass("%s\n", __func__);
}
// 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");
ksft_test_result_pass("%s\n", __func__);
}
// This test validates that we can remap over only a portion of a mapping.
static void mremap_dontunmap_partial_mapping_overwrite(void)
{
/*
* source mapping:
* ---------
* |aaaaa|
* ---------
* dest mapping initially:
* -----------
* |XXXXXXXXXX|
* ------------
* Source to become:
* ---------
* |00000|
* ---------
* With the destination mapping containing 5 pages of As.
* ------------
* |aaaaaXXXXX|
* ------------
*/
void *source_mapping =
mmap(NULL, 5 * page_size, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
BUG_ON(source_mapping == MAP_FAILED, "mmap");
memset(source_mapping, 'a', 5 * page_size);
void *dest_mapping =
mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
BUG_ON(dest_mapping == MAP_FAILED, "mmap");
memset(dest_mapping, 'X', 10 * page_size);
// We will grab the last 5 pages of the source and move them.
void *remapped_mapping =
mremap(source_mapping, 5 * page_size,
5 * page_size,
MREMAP_DONTUNMAP | MREMAP_MAYMOVE | MREMAP_FIXED, dest_mapping);
BUG_ON(dest_mapping == MAP_FAILED, "mremap");
BUG_ON(dest_mapping != remapped_mapping, "expected to remap to dest_mapping");
BUG_ON(check_region_contains_byte(source_mapping, 5 * page_size, 0) !=
0, "first 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");
// Finally the last 5 pages shouldn't have been touched.
BUG_ON(check_region_contains_byte(dest_mapping + (5 * page_size),
5 * page_size, 'X') != 0,
"dest mapping should have retained the last 5 pages");
BUG_ON(munmap(dest_mapping, 10 * page_size) == -1,
"unable to unmap destination mapping");
BUG_ON(munmap(source_mapping, 5 * page_size) == -1,
"unable to unmap source mapping");
ksft_test_result_pass("%s\n", __func__);
}
int main(void)
{
ksft_print_header();
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) {
ksft_print_msg("No kernel support for MREMAP_DONTUNMAP\n");
ksft_finished();
}
ksft_set_plan(5);
// 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_shmem();
mremap_dontunmap_simple_fixed();
mremap_dontunmap_partial_mapping();
mremap_dontunmap_partial_mapping_overwrite();
BUG_ON(munmap(page_buffer, page_size) == -1,
"unable to unmap page buffer");
ksft_finished();
}
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