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

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Message-ID: <ac9b16a7-f294-44d4-8243-488db97a009e@collabora.com>
Date: Sun, 7 Apr 2024 02:23:13 +0500
From: Muhammad Usama Anjum <usama.anjum@...labora.com>
To: Dev Jain <dev.jain@....com>, shuah@...nel.org,
 linux-arm-kernel@...ts.infradead.org
Cc: Muhammad Usama Anjum <usama.anjum@...labora.com>,
 linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
 Anshuman.Khandual@....com, suzuki.poulose@....com, ryan.roberts@....com,
 rob.herring@....com, Catalin.Marinas@....com, broonie@...nel.org,
 will@...nel.org, mark.rutland@....com
Subject: Re: [PATCH 1/4] selftests/arm: Add mm test

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@....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@....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.

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

-- 
BR,
Muhammad Usama Anjum