On 4/10/24 09:45, Dev Jain wrote:
On 4/7/24 02:53, Muhammad Usama Anjum wrote:
On 4/5/24 1:44 PM, Dev Jain wrote:
This patch tests the 4GB VA restriction for 32-bit processes; it is required to test the compat layer, whether the kernel knows that it is running a 32-bit process or not. Chunks are allocated until the VA gets exhausted; mmap must fail beyond 4GB. This is asserted against the VA mappings found in /proc/self/maps.
Signed-off-by: Dev Jain dev.jain@arm.com
tools/testing/selftests/arm/mm/compat_va.c | 94 ++++++++++++++++++++++ 1 file changed, 94 insertions(+) create mode 100644 tools/testing/selftests/arm/mm/compat_va.c
diff --git a/tools/testing/selftests/arm/mm/compat_va.c b/tools/testing/selftests/arm/mm/compat_va.c new file mode 100644 index 000000000000..3a78f240bc87 --- /dev/null +++ b/tools/testing/selftests/arm/mm/compat_va.c @@ -0,0 +1,94 @@ +// SPDX-License-Identifier: GPL-2.0 +/*
- Copyright (C) 2024 ARM Limited
- Author : Dev Jain dev.jain@arm.com
- Tests 4GB VA restriction for 32 bit process
- */
+#define _GNU_SOURCE +#include <stdio.h> +#include <stdlib.h> +#include <unistd.h> +#include <sys/mman.h>
+#include <linux/sizes.h> +#include <kselftest.h>
+#define MAP_CHUNK_SIZE SZ_1M +#define NR_CHUNKS_4G (SZ_1G / MAP_CHUNK_SIZE) * 4 /* prevent overflow */
+static int validate_address_hint(void) +{ + char *ptr;
+ ptr = mmap((void *) (1UL << 29), MAP_CHUNK_SIZE, PROT_READ | + PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ if (ptr == MAP_FAILED) + return 0;
+ return 1;
Usually we return negative value instead of positive one which indicates error situation.
+}
+int main(int argc, char *argv[]) +{ + char *ptr[NR_CHUNKS_4G + 3]; + char line[1000]; + const char *file_name; + int chunks; + FILE *file; + int i;
+ ksft_print_header(); + ksft_set_plan(1);
There are multiple test cases. Instead of saying there is only 1 test. There should be multiple ksft_test_result{_pass,_fail} statements for each sub-tests.
My initial idea was to treat this as a single logical test, as I
am asserting the restriction on the number of chunks against
the VMAs. I guess your approach is cleaner; thanks.
Thinking again, using a lot of return statements is in fact making the code easier
to follow. If I just set a variable ret = 0/1 and use it to pass or fail, I'll have to
unnecessarily use a lot of if/else statements. Take a look at the examples below.
+ /* try allocation beyond 4 GB */ + for (i = 0; i < NR_CHUNKS_4G + 3; ++i) { + ptr[i] = mmap(NULL, MAP_CHUNK_SIZE, PROT_READ | PROT_WRITE, + MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ if (ptr[i] == MAP_FAILED) { + if (validate_address_hint()) + ksft_exit_fail_msg("VA exhaustion failed\n"); + break;
I will have to set ret value here, forcing two statements inside the if block.
+ } + }
+ chunks = i; + if (chunks >= NR_CHUNKS_4G) { + ksft_test_result_fail("mmapped chunks beyond 4GB\n"); + ksft_finished(); + }
+ /* parse /proc/self/maps, confirm 32 bit VA mappings */ + file_name = "/proc/self/maps"; + file = fopen(file_name, "r"); + if (file == NULL) + ksft_exit_fail_msg("/proc/self/maps cannot be opened\n");
I will have to set ret here, and enclose the below while statement inside
an else block. In short, saving the value of ret will require if/else blocks
if I were to use it in the end in ksft_test_result(). When I use ksft_exit
statements, it is clear that a problem was spotted here, and there is
no need to study the remaining code.
+ while (fgets(line, sizeof(line), file)) { + const char *whitespace_loc, *hyphen_loc;
+ hyphen_loc = strchr(line, '-'); + whitespace_loc = strchr(line, ' ');
+ if (!(hyphen_loc && whitespace_loc)) { + ksft_test_result_skip("Unexpected format"); + ksft_finished();
I'm unable to follow as there are too many return statements. If you divide the test into multiple sub-tests, you can skip/pass/fail each sub-test easily.
+ }
+ if ((hyphen_loc - line > 8) || + (whitespace_loc - hyphen_loc) > 9) { + ksft_test_result_fail("Memory map more than 32 bits\n"); + ksft_finished(); + } + }
+ for (int i = 0; i < chunks; ++i) + munmap(ptr[i], MAP_CHUNK_SIZE);
+ ksft_test_result_pass("Test\n"); + ksft_finished(); +}
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