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X-CSE-ConnectionGUID: m5kWUH8TQa6RQ9t9L0NLBA== X-CSE-MsgGUID: E5yKo1IlTb2TZx2O/GgD8Q== X-IronPort-AV: E=McAfee;i="6800,10657,11575"; a="84672481" X-IronPort-AV: E=Sophos;i="6.18,321,1751266800"; d="scan'208";a="84672481" Received: from fmviesa003.fm.intel.com ([10.60.135.143]) by orvoesa101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 07 Oct 2025 11:28:40 -0700 X-CSE-ConnectionGUID: SuKf2V8RQlqfzmERYVru0g== X-CSE-MsgGUID: 2M0/4sqsSBuh1xIVdrUQ3g== X-ExtLoop1: 1 Received: from cmdeoliv-mobl4.amr.corp.intel.com (HELO [10.125.110.162]) ([10.125.110.162]) by fmviesa003-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 07 Oct 2025 11:28:37 -0700 Message-ID: <5d95d421-1413-46de-a578-c2a0e44e3aa1@intel.com> Date: Tue, 7 Oct 2025 11:28:36 -0700 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 01/15] x86/cpu: Enumerate the LASS feature bits To: "Edgecombe, Rick P" , "Mehta, Sohil" , "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "x86@kernel.org" , "dave.hansen@linux.intel.com" Cc: "corbet@lwn.net" , "ardb@kernel.org" , "david.laight.linux@gmail.com" , "luto@kernel.org" , "jpoimboe@kernel.org" , "andrew.cooper3@citrix.com" , "Luck, Tony" , "alexander.shishkin@linux.intel.com" , "kas@kernel.org" , "seanjc@google.com" , "rdunlap@infradead.org" , "dwmw@amazon.co.uk" , "vegard.nossum@oracle.com" , "xin@zytor.com" , "linux-kernel@vger.kernel.org" , "linux-doc@vger.kernel.org" , "kees@kernel.org" , "hpa@zytor.com" , "peterz@infradead.org" , "linux-efi@vger.kernel.org" , "geert@linux-m68k.org" References: <20251007065119.148605-1-sohil.mehta@intel.com> <20251007065119.148605-2-sohil.mehta@intel.com> <47fb7efd89698f46a305ca446d0e4471d1f24fbb.camel@intel.com> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/7/25 11:19, Edgecombe, Rick P wrote: >> { X86_FEATURE_SPEC_CTRL_SSBD, X86_FEATURE_SPEC_CTRL }, >> + { X86_FEATURE_LASS, X86_FEATURE_SMAP }, > Aha! So SMAP is required for LASS. This makes the stac/clac patch make more > sense. Please those comments less seriously. Although I think a comment is still > not unwarranted. STAC/CLAC are also architected to: #UD - If CPUID.(EAX=07H, ECX=0H):EBX.SMAP[bit 20] = 0. So, even though LASS _technically_ doesn't require SMAP, it would be a real pain without SMAP and STAC/CLAC. Thus, this series relies on SMAP being present. Actually, it might be worth breaking this dependency hunk out into its own patch, just so there's a nice clean place to discuss this.