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Message-ID: <2dfae66f-1e34-40e5-a6a1-344ff4422028@arm.com>
Date: Wed, 10 Apr 2024 09:45:41 +0530
From: Dev Jain <dev.jain@....com>
To: Muhammad Usama Anjum <usama.anjum@...labora.com>, shuah@...nel.org,
linux-arm-kernel@...ts.infradead.org
Cc: 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 4/7/24 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@....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.
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();
>> +}
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