Re: [PATCH 1/4] selftests/arm: Add mm test

[Dev Jain <dev.jain@arm.com>]

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.

>
>> +
>> +	/* 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;
>> +		}
>> +	}
>> +
>> +	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");
>> +
>> +	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();
>> +}