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X-CSE-ConnectionGUID: rTikGiDQQIS6KALBmrwrzg== X-CSE-MsgGUID: VTYdDhSmS5ONL+92zg+APw== X-IronPort-AV: E=McAfee;i="6700,10204,11263"; a="32514314" X-IronPort-AV: E=Sophos;i="6.12,173,1728975600"; d="scan'208";a="32514314" Received: from orviesa001.jf.intel.com ([10.64.159.141]) by orvoesa110.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Nov 2024 13:46:22 -0800 X-CSE-ConnectionGUID: fYOo4fxmRIK4ExmiCvqffA== X-CSE-MsgGUID: GOoWo6KRScyI6DSdi6zdnA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.12,173,1728975600"; d="scan'208";a="127899467" Received: from mdroper-mobl2.amr.corp.intel.com (HELO [10.124.220.45]) ([10.124.220.45]) by smtpauth.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Nov 2024 13:46:22 -0800 Message-ID: <49690bcc-e2ac-43f6-95da-3711801e195a@intel.com> Date: Thu, 21 Nov 2024 13:46:17 -0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: Dave Hansen Subject: Re: [PATCH 04/11] x86/acpi: Check MWAIT feature instead of CPUID level To: Sean Christopherson , Dave Hansen Cc: linux-kernel@vger.kernel.org, x86@kernel.org, tglx@linutronix.de, bp@alien8.de, rafael@kernel.org, lenb@kernel.org, dave.jiang@intel.com, irenic.rajneesh@gmail.com, david.e.box@intel.com References: <20241120195327.26E06A69@davehans-spike.ostc.intel.com> <20241120195332.929A7C44@davehans-spike.ostc.intel.com> Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/21/24 07:33, Sean Christopherson wrote: > On Wed, Nov 20, 2024, Dave Hansen wrote: >> From: Dave Hansen >> >> I think this code is possibly buggy. The CPU could have a high >> c->cpuid_level and not support MWAIT at all. > > Reading CPUID.0x5 is totally fine in that case though. Wasteful and pointless, > but functionally ok. If the CPU provides non-zero values when MWAIT is unsupported, > then that's a broken CPU. That's a good point. I was mostly worried about consuming *bad* data from CPUID.5, but the leaf check takes care of that now. >> diff -puN arch/x86/kernel/acpi/cstate.c~mwait-leaf-checks-3 arch/x86/kernel/acpi/cstate.c >> --- a/arch/x86/kernel/acpi/cstate.c~mwait-leaf-checks-3 2024-11-20 11:44:17.225650902 -0800 >> +++ b/arch/x86/kernel/acpi/cstate.c 2024-11-20 11:44:17.225650902 -0800 >> @@ -173,7 +173,7 @@ int acpi_processor_ffh_cstate_probe(unsi >> struct cpuinfo_x86 *c = &cpu_data(cpu); >> long retval; >> >> - if (!cpu_cstate_entry || c->cpuid_level < CPUID_MWAIT_LEAF) >> + if (!cpu_cstate_entry || cpu_has(c, X86_FEATURE_MWAIT)) > > Someone didn't test this :-) Guilty. I'll just drop this.