linux-kernel - Re: [PATCH v5 5/5] selftests/resctrl: Add non-contiguous CBMs CAT test

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Date: Fri, 9 Feb 2024 09:21:16 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>,
	<shuah@...nel.org>, <fenghua.yu@...el.com>
CC: <linux-kselftest@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<ilpo.jarvinen@...ux.intel.com>
Subject: Re: [PATCH v5 5/5] selftests/resctrl: Add non-contiguous CBMs CAT
 test

Hi Maciej,

On 2/9/2024 6:02 AM, Maciej Wieczor-Retman wrote:

..

> diff --git a/tools/testing/selftests/resctrl/cat_test.c b/tools/testing/selftests/resctrl/cat_test.c
> index 39fc9303b8e8..d4b7bf8a6780 100644
> --- a/tools/testing/selftests/resctrl/cat_test.c
> +++ b/tools/testing/selftests/resctrl/cat_test.c
> @@ -294,6 +294,71 @@ static int cat_run_test(const struct resctrl_test *test, const struct user_param
>  	return ret;
>  }
>  
> +static int noncont_cat_run_test(const struct resctrl_test *test,
> +				const struct user_params *uparams)
> +{
> +	unsigned long full_cache_mask, cont_mask, noncont_mask;
> +	unsigned int eax, ebx, ecx, edx, ret, sparse_masks;

I missed that "ret" is "unsigned int" while the test expects it to
be signed ("if (ret < 0)") and it is used to have return value of functions
that return < 0 on error.


> +	char schemata[64];
> +	int bit_center;
> +
> +	/* Check to compare sparse_masks content to CPUID output. */
> +	ret = resource_info_unsigned_get(test->resource, "sparse_masks", &sparse_masks);
> +	if (ret)
> +		return ret;
> +
> +	if (!strcmp(test->resource, "L3"))
> +		__cpuid_count(0x10, 1, eax, ebx, ecx, edx);
> +	else if (!strcmp(test->resource, "L2"))
> +		__cpuid_count(0x10, 2, eax, ebx, ecx, edx);
> +	else
> +		return -EINVAL;
> +
> +	if (sparse_masks != ((ecx >> 3) & 1)) {
> +		ksft_print_msg("CPUID output doesn't match 'sparse_masks' file content!\n");
> +		return 1;
> +	}
> +
> +	/* Write checks initialization. */
> +	ret = get_full_cbm(test->resource, &full_cache_mask);
> +	if (ret < 0)
> +		return ret;
> +	bit_center = count_bits(full_cache_mask) / 2;

It would be nice if no new static check issues are introduced into the
resctrl selftests. I did a quick check and this is a problematic portion.
We know that the full_cache_mask cannot have zero bits but it is not
obvious to the checkers, thus thinking that bit_center may be zero
resulting in a bit shift of "-2" bits attempt later on. Could you please
add some error checking to ensure expected values to avoid extra noise from
checkers when this code lands upstream?

Thank you

Reinette