Re: [PATCH v2 1/2] selftests/resctrl: Add L3_CBM_VALIDATE to check CBM writes

[Reinette Chatre <reinette.chatre@intel.com>]

Hi Richard,

On 8/10/26 2:51 AM, Richard Cheng wrote:
> Add L3_CBM_VALIDATE to verify that resctrl enforces the L3 CBM rules
> advertised by cbm_mask and min_cbm_bits.
> 
> Confirm that the full mask is accepted. Check the empty mask according
> to min_cbm_bits, and confirm that out-of-range and undersized masks are
> rejected.
> 
> This catches inconsistencies between the advertised capabilities and
> schemata validation.
> 
> Signed-off-by: Richard Cheng <icheng@nvidia.com>
> ---

....

> diff --git a/tools/testing/selftests/resctrl/cat_test.c b/tools/testing/selftests/resctrl/cat_test.c
> index 371a2f26dc47..a06c57954740 100644
> --- a/tools/testing/selftests/resctrl/cat_test.c
> +++ b/tools/testing/selftests/resctrl/cat_test.c
> @@ -357,6 +357,89 @@ static bool noncont_cat_feature_check(const struct resctrl_test *test)
>  	return resource_info_file_exists(test->resource, "sparse_masks");
>  }
>  
> +/*
> + * L3_CBM_VALIDATE - Verify L3 CBM write validation.
> + *
> + * A full CBM must be accepted. An empty CBM is valid only when min_cbm_bits
> + * is zero. Masks with bits outside cbm_mask or fewer than min_cbm_bits must
> + * be rejected.
> + */
> +static int cbm_validate_run_test(const struct resctrl_test *test,
> +				 const struct user_params *uparams)

Nothing about this function (except the hardcoded string in the final "Pass:"
message) is specific to L3. It looks to me as though an L2 variant of this test can
easily be added with just a new "struct resctrl_test l2_cbm_validate_test"? (more below)
The "Pass:" message can just use resctrl_test::resource instead of the hardcoded "L3".

> +{
> +	unsigned int min_cbm_bits, contiguous_bits;
> +	unsigned long long invalid_mask;
> +	unsigned int count_of_bits;
> +	unsigned long full_mask;
> +	unsigned int start;
> +	char schemata[64];
> +	int ret;
> +
> +	ret = get_full_cbm(test->resource, &full_mask);
> +	if (ret)
> +		return ret;
> +
> +	ret = resource_info_unsigned_get(test->resource, "min_cbm_bits",
> +					 &min_cbm_bits);
> +	if (ret)
> +		return ret;
> +
> +	count_of_bits = count_bits(full_mask);
> +
> +	/* A valid full CBM must be accepted. */
> +	snprintf(schemata, sizeof(schemata), "%lx", full_mask);
> +	if (write_schemata("", schemata, uparams->cpu, test->resource)) {
> +		ksft_print_msg("Valid CBM 0x%lx was rejected\n", full_mask);
> +		return KSFT_FAIL;
> +	}
> +
> +	ret = write_schemata("", "0", uparams->cpu, test->resource);
> +	if (min_cbm_bits && !ret) {
> +		ksft_print_msg("Empty CBM was accepted, must be rejected\n");
> +		return KSFT_FAIL;
> +	}
> +	if (!min_cbm_bits && ret) {
> +		ksft_print_msg("Empty CBM was rejected, must be accepted\n");
> +		return KSFT_FAIL;
> +	}
> +
> +	/* A mask with a bit outside cbm_mask must be rejected. */
> +	invalid_mask = (unsigned long long)full_mask | (1ULL << count_of_bits);
> +	snprintf(schemata, sizeof(schemata), "%llx", invalid_mask);
> +	if (!write_schemata("", schemata, uparams->cpu, test->resource)) {
> +		ksft_print_msg("Out-of-range CBM 0x%llx was accepted, must be rejected\n",
> +			       invalid_mask);
> +		return KSFT_FAIL;
> +	}
> +
> +	/*
> +	 * When min_cbm_bits is greater than one, a non-empty mask with fewer
> +	 * bits must be rejected.
> +	 */
> +	if (min_cbm_bits > 1) {
> +		contiguous_bits = count_contiguous_bits(full_mask, &start);
> +		if (contiguous_bits < min_cbm_bits) {
> +			ksft_print_msg("Full CBM has %u contiguous bits, fewer than "
> +				       "min_cbm_bits=%u\n",

Please do not split this message across two lines. If you want to appease checkpatch.pl you
can merge the two lines and drop "fewer than". For example,
			ksft_print_msg("Full CBM has %u contiguous bits, min_cbm_bits=%u\n",

Just merging them as-is is fine also. You will find this file to have messages with even
longer lines (see noncont_cat_run_test()).

> +				       contiguous_bits, min_cbm_bits);
> +			return KSFT_FAIL;
> +		}
> +
> +		invalid_mask = create_bit_mask(start, min_cbm_bits - 1);
> +		snprintf(schemata, sizeof(schemata), "%llx", invalid_mask);
> +		if (!write_schemata("", schemata, uparams->cpu,
> +				    test->resource)) {
> +			ksft_print_msg("CBM 0x%llx with too few bits was accepted\n",
> +				       invalid_mask);
> +			return KSFT_FAIL;
> +		}
> +	}
> +
> +	ksft_print_msg("Pass: L3 CBM writes were validated correctly\n");
> +
> +	return 0;
> +}
> +
>  struct resctrl_test l3_cat_test = {
>  	.name = "L3_CAT",
>  	.group = "CAT",
> @@ -366,6 +449,14 @@ struct resctrl_test l3_cat_test = {
>  	.cleanup = cat_test_cleanup,
>  };
>  
> +struct resctrl_test l3_cbm_validate_test = {
> +	.name = "L3_CBM_VALIDATE",
> +	.group = "CAT",
> +	.resource = "L3",
> +	.feature_check = test_resource_feature_check,
> +	.run_test = cbm_validate_run_test,
> +};

As hinted earlier, something like below (with supporting changes in resctrl.h and resctrl_tests.c)
should be all that is needed to expand coverage to L2:

struct resctrl_test l2_cbm_validate_test = {
	.name = "L2_CBM_VALIDATE",
	.group = "CAT",
	.resource = "L2",
	.feature_check = test_resource_feature_check,
	.run_test = cbm_validate_run_test,
};


> +
>  struct resctrl_test l3_noncont_cat_test = {
>  	.name = "L3_NONCONT_CAT",
>  	.group = "CAT",
> diff --git a/tools/testing/selftests/resctrl/resctrl.h b/tools/testing/selftests/resctrl/resctrl.h
> index 175101022bf3..a6fc688ed997 100644
> --- a/tools/testing/selftests/resctrl/resctrl.h
> +++ b/tools/testing/selftests/resctrl/resctrl.h
> @@ -240,6 +240,7 @@ extern struct resctrl_test mbm_test;
>  extern struct resctrl_test mba_test;
>  extern struct resctrl_test cmt_test;
>  extern struct resctrl_test l3_cat_test;
> +extern struct resctrl_test l3_cbm_validate_test;
>  extern struct resctrl_test l3_noncont_cat_test;
>  extern struct resctrl_test l2_noncont_cat_test;
>  
> diff --git a/tools/testing/selftests/resctrl/resctrl_tests.c b/tools/testing/selftests/resctrl/resctrl_tests.c
> index dbcd5eea9fbc..57a4d0815b67 100644
> --- a/tools/testing/selftests/resctrl/resctrl_tests.c
> +++ b/tools/testing/selftests/resctrl/resctrl_tests.c
> @@ -19,6 +19,7 @@ static struct resctrl_test *resctrl_tests[] = {
>  	&mba_test,
>  	&cmt_test,
>  	&l3_cat_test,
> +	&l3_cbm_validate_test,
>  	&l3_noncont_cat_test,
>  	&l2_noncont_cat_test,
>  };

Reinette