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Message-ID: <ad272dc1-1b85-41ef-8454-4888a5ab95ee@intel.com>
Date: Tue, 12 Mar 2024 09:07:15 -0700
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH] selftests: x86: skip the tests if prerequisites aren't
 fulfilled
Content-Language: en-US
To: Muhammad Usama Anjum <usama.anjum@collabora.com>, Shuah Khan
	<shuah@kernel.org>, Dave Hansen <dave.hansen@linux.intel.com>, "Kirill A.
 Shutemov" <kirill.shutemov@linux.intel.com>, "Peter Zijlstra (Intel)"
	<peterz@infradead.org>, Weihong Zhang <weihong.zhang@intel.com>, Binbin Wu
	<binbin.wu@linux.intel.com>, angquan yu <angquan21@gmail.com>
CC: <kernel@collabora.com>, <linux-kselftest@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>
References: <20240307183730.2858264-1-usama.anjum@collabora.com>
 <dc8d122a-22b7-4d17-abd9-66262af0b058@intel.com>
 <c3362840-365e-40cb-80fe-895aa2d979ec@collabora.com>
 <1cacbd08-1131-4be4-b318-58c05afda2de@intel.com>
 <21f8dbe3-9de2-41ad-a8bd-61d66cb38e90@collabora.com>
From: "Chang S. Bae" <chang.seok.bae@intel.com>
In-Reply-To: <21f8dbe3-9de2-41ad-a8bd-61d66cb38e90@collabora.com>
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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