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 <[email protected]>
> ---
> 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.
