Re: [PATCH v2 3/3] selftests/resctrl: Recognise aarch64 as a vendor for L3_NONCONT_CAT

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

On Thu, 28 May 2026, Richard Cheng wrote:

> aarch64 has no vendor_id in /proc/cpuinfo, so detect_vendor() returns 0
> and arch_supports_noncont_cat() falls through to "return false".
> L3_NONCONT_CAT therefore spuriously fails on every ARM MPAM platform.
> 
> Define ARCH_ARM, short-circuit detect_vendor() to it on aarch64, and
> add it to the AMD/Hygon always-supports early-out in
> arch_supports_noncont_cat().
> 
> aarch64 has many implementers (ARM 0x41, NVIDIA 0x43, etc.), but MPAM
> mandates non-contiguous CPBM uniformly, so per-implementer handling is
> not needed here.
> 
> Signed-off-by: Richard Cheng <icheng@nvidia.com>
> ---
>  tools/testing/selftests/resctrl/cat_test.c      |  9 +++++++--
>  tools/testing/selftests/resctrl/resctrl.h       |  1 +
>  tools/testing/selftests/resctrl/resctrl_tests.c | 11 +++++++++++
>  3 files changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/resctrl/cat_test.c b/tools/testing/selftests/resctrl/cat_test.c
> index dc414e55ae94..ce66016dbd88 100644
> --- a/tools/testing/selftests/resctrl/cat_test.c
> +++ b/tools/testing/selftests/resctrl/cat_test.c
> @@ -292,8 +292,13 @@ static bool arch_supports_noncont_cat(const struct resctrl_test *test)
>  {
>  	unsigned int vendor_id = get_vendor();
>  
> -	/* AMD and Hygon always support non-contiguous CBM. */
> -	if (vendor_id == ARCH_AMD || vendor_id == ARCH_HYGON)
> +	/*
> +	 * AMD and Hygon always support non-contiguous CBM. ARM/MPAM defines
> +	 * MPAMCFG_CPBM as a bitmap with no contiguity constraint per ARM
> +	 * DDI 0598.
> +	 */
> +	if (vendor_id == ARCH_AMD || vendor_id == ARCH_HYGON ||
> +	    vendor_id == ARCH_ARM)
>  		return true;
>  
>  #if defined(__i386__) || defined(__x86_64__) /* arch */
> diff --git a/tools/testing/selftests/resctrl/resctrl.h b/tools/testing/selftests/resctrl/resctrl.h
> index afe635b6e48d..670e5b128b4d 100644
> --- a/tools/testing/selftests/resctrl/resctrl.h
> +++ b/tools/testing/selftests/resctrl/resctrl.h
> @@ -40,6 +40,7 @@
>  #define ARCH_INTEL	BIT(0)
>  #define ARCH_AMD	BIT(1)
>  #define ARCH_HYGON	BIT(2)
> +#define ARCH_ARM	BIT(3)
>  
>  #define END_OF_TESTS	1
>  
> diff --git a/tools/testing/selftests/resctrl/resctrl_tests.c b/tools/testing/selftests/resctrl/resctrl_tests.c
> index dbcd5eea9fbc..b28dae83d0a4 100644
> --- a/tools/testing/selftests/resctrl/resctrl_tests.c
> +++ b/tools/testing/selftests/resctrl/resctrl_tests.c
> @@ -34,6 +34,17 @@ static unsigned int detect_vendor(void)
>  	if (initialized)
>  		return vendor_id;
>  
> +#if defined(__aarch64__)
> +	/*
> +	 * aarch64 has no userspace vendor_id in /proc/cpuinfo. MPAM-capable
> +	 * ARM implementations follow ARM DDI 0598; treat all aarch64 builds
> +	 * as a single vendor for the purposes of resctrl selftests.
> +	 */
> +	vendor_id = ARCH_ARM;
> +	initialized = true;
> +	return vendor_id;
> +#endif

It would be better to create a detect_aarch64() function and put 
the ifdeffery inside it so it returns either true or false here.

> +
>  	inf = fopen("/proc/cpuinfo", "r");
>  	if (!inf) {
>  		vendor_id = 0;
> 

-- 
 i.