Re: [PATCH] selftests: x86: skip the tests if prerequisites aren't fulfilled

[Chang S. Bae]

On 3/12/2024 2:26 AM, Muhammad Usama Anjum wrote:
>
> How can we check if AMX is available or not?

After a successful check_cpuid_xsave(), examining CPUID(eax=0xd, ecx=0) 
EDX: EAX, which reports the support bits of XCR0, can give assurance of 
AMX availability. Perhaps, this change is considerable on top of your patch:

static int check_cpuid_xtiledata(void)
{
        uint32_t eax, ebx, ecx, edx;
+       uint64_t xfeatures;

        __cpuid_count(CPUID_LEAF_XSTATE, CPUID_SUBLEAF_XSTATE_USER,
                      eax, ebx, ecx, edx);

+       xfeatures = eax + ((uint64_t)edx << 32);
+       if ((xfeatures & XFEATURE_MASK_XTILE) != XFEATURE_MASK_XTILE) {
+               ksft_print_msg("no AMX support\n");
+               return -1;
+       }

Nevertheless, I still believe that using arch_prctl(ARCH_GET_XCOMP_SUPP, 
..) remains a simple and legitimate approach for directly checking 
dynamic feature support from the kernel: 
https://docs.kernel.org/arch/x86/xstate.html

Thanks,
Chang