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

[Dev Jain]

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@xxxxxxx>
> > ---
> >   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@xxxxxxx>
> > + *
> > + * 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();
> > +}