Messages in this thread | | | Date | Wed, 17 Apr 2024 10:23:58 +0530 | Subject | Re: [PATCH 1/4] selftests/arm: Add mm test | From | Dev Jain <> |
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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(); >>> +} > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
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