From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 83EAE2253E9; Tue, 24 Jun 2025 05:12:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750741938; cv=none; b=QfoSk5K72JsPq9eajE5mX4xIiUAimvSh5h1RJIvsEyoZ9SRFKZxmU2TqNpTlXnaakQBAfSCo5xNT+bjuoNp+QKiNlx7ftGcgczZjacrlFzubPoksGdwxXNMbMSFOP+iN1H+jCVwNPBsa9pyT/XqkHG15O9pwbgE/14IqwY2RA7w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750741938; c=relaxed/simple; bh=R9jolyBeToWMbGoUct/gN1lHCvix5RrQdEKK1lIPCbU=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=XdnGDUC0UhgLCggSLYhmYbR5eLIXWcG/MDYcJ5rhfQh6my28pavNCVZiy3tGM/W0Uz0qsRAIc7DCOVXNCdIgpRihw6HwpvL+LITtTa6D9vvrJmB91q9l6selmnO4g+0vqAEZ7a5xYym36ju36vifWjtYbHAo8nWgZDblIytQrj8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com; spf=pass smtp.mailfrom=zytor.com; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b=f6kUcw3d; arc=none smtp.client-ip=198.137.202.136 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=zytor.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b="f6kUcw3d" Received: from [192.168.7.202] ([71.202.166.45]) (authenticated bits=0) by mail.zytor.com (8.18.1/8.17.1) with ESMTPSA id 55O5B9EQ1214832 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Mon, 23 Jun 2025 22:11:09 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 55O5B9EQ1214832 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2025062101; t=1750741873; bh=hyBq9kZTajfYMQM3o1zuSl07WmRWLe3Uj8KJJs7+GtI=; h=Date:Subject:From:To:Cc:References:In-Reply-To:From; b=f6kUcw3dSL+EV9uGfmbKUBMJgwgWc6UN73DVS6weHEHIb0jsrrDw9NrtKF6AFJvCw JnoJ3nFKC04S9WVqdfOZtnvgnrHnj14GFYF7w3m7WUNICB3MYX+oquhZgnLJZ84smm uotpg9ZpzzrGlwPnbcPZRZZsqcKrc2gC+kExlQx4EzuSZ0almAaMM05OIMxosP3nBz bDQXKCgLUVij5bsKji1WRwegftu0ZhWSan+nwMKg3Xadf77LkyLX/T9LKI0PxQu7x3 PU6Fag4XBwD82PGoElGA4yGDKbYYsksS5xgVj6A1pF7+czgVchdaAw89AzXNm2/85C vSVZpF1aVJwqw== Message-ID: Date: Mon, 23 Jun 2025 22:11:08 -0700 Precedence: bulk X-Mailing-List: linux-efi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHv6 01/16] x86/cpu: Enumerate the LASS feature bits From: Xin Li To: "H. Peter Anvin" , "Kirill A. Shutemov" Cc: Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Peter Zijlstra , Ard Biesheuvel , "Paul E. McKenney" , Josh Poimboeuf , Xiongwei Song , Xin Li , "Mike Rapoport (IBM)" , Brijesh Singh , Michael Roth , Tony Luck , Alexey Kardashevskiy , Alexander Shishkin , Jonathan Corbet , Sohil Mehta , Ingo Molnar , Pawan Gupta , Daniel Sneddon , Kai Huang , Sandipan Das , Breno Leitao , Rick Edgecombe , Alexei Starovoitov , Hou Tao , Juergen Gross , Vegard Nossum , Kees Cook , Eric Biggers , Jason Gunthorpe , "Masami Hiramatsu (Google)" , Andrew Morton , Luis Chamberlain , Yuntao Wang , Rasmus Villemoes , Christophe Leroy , Tejun Heo , Changbin Du , Huang Shijie , Geert Uytterhoeven , Namhyung Kim , Arnaldo Carvalho de Melo , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-efi@vger.kernel.org, linux-mm@kvack.org References: <20250620135325.3300848-1-kirill.shutemov@linux.intel.com> <20250620135325.3300848-2-kirill.shutemov@linux.intel.com> <73796800-819b-4433-b0ef-db852336d7a4@zytor.com> <0A71C898-B587-4292-AB05-6CA46BBD6F88@zytor.com> <5529aa92-191d-4120-a005-28fe5c209a4f@zytor.com> Content-Language: en-US Autocrypt: addr=xin@zytor.com; keydata= xsDNBGUPz1cBDACS/9yOJGojBFPxFt0OfTWuMl0uSgpwk37uRrFPTTLw4BaxhlFL0bjs6q+0 2OfG34R+a0ZCuj5c9vggUMoOLdDyA7yPVAJU0OX6lqpg6z/kyQg3t4jvajG6aCgwSDx5Kzg5 Rj3AXl8k2wb0jdqRB4RvaOPFiHNGgXCs5Pkux/qr0laeFIpzMKMootGa4kfURgPhRzUaM1vy bsMsL8vpJtGUmitrSqe5dVNBH00whLtPFM7IbzKURPUOkRRiusFAsw0a1ztCgoFczq6VfAVu raTye0L/VXwZd+aGi401V2tLsAHxxckRi9p3mc0jExPc60joK+aZPy6amwSCy5kAJ/AboYtY VmKIGKx1yx8POy6m+1lZ8C0q9b8eJ8kWPAR78PgT37FQWKYS1uAroG2wLdK7FiIEpPhCD+zH wlslo2ETbdKjrLIPNehQCOWrT32k8vFNEMLP5G/mmjfNj5sEf3IOKgMTMVl9AFjsINLHcxEQ 6T8nGbX/n3msP6A36FDfdSEAEQEAAc0WWGluIExpIDx4aW5Aenl0b3IuY29tPsLBDQQTAQgA NxYhBIUq/WFSDTiOvUIqv2u9DlcdrjdRBQJlD89XBQkFo5qAAhsDBAsJCAcFFQgJCgsFFgID AQAACgkQa70OVx2uN1HUpgv/cM2fsFCQodLArMTX5nt9yqAWgA5t1srri6EgS8W3F+3Kitge tYTBKu6j5BXuXaX3vyfCm+zajDJN77JHuYnpcKKr13VcZi1Swv6Jx1u0II8DOmoDYLb1Q2ZW v83W55fOWJ2g72x/UjVJBQ0sVjAngazU3ckc0TeNQlkcpSVGa/qBIHLfZraWtdrNAQT4A1fa sWGuJrChBFhtKbYXbUCu9AoYmmbQnsx2EWoJy3h7OjtfFapJbPZql+no5AJ3Mk9eE5oWyLH+ QWqtOeJM7kKvn/dBudokFSNhDUw06e7EoVPSJyUIMbYtUO7g2+Atu44G/EPP0yV0J4lRO6EA wYRXff7+I1jIWEHpj5EFVYO6SmBg7zF2illHEW31JAPtdDLDHYcZDfS41caEKOQIPsdzQkaQ oW2hchcjcMPAfyhhRzUpVHLPxLCetP8vrVhTvnaZUo0xaVYb3+wjP+D5j/3+hwblu2agPsaE vgVbZ8Fx3TUxUPCAdr/p73DGg57oHjgezsDNBGUPz1gBDAD4Mg7hMFRQqlzotcNSxatlAQNL MadLfUTFz8wUUa21LPLrHBkUwm8RujehJrzcVbPYwPXIO0uyL/F///CogMNx7Iwo6by43KOy g89wVFhyy237EY76j1lVfLzcMYmjBoTH95fJC/lVb5Whxil6KjSN/R/y3jfG1dPXfwAuZ/4N cMoOslWkfZKJeEut5aZTRepKKF54T5r49H9F7OFLyxrC/uI9UDttWqMxcWyCkHh0v1Di8176 jjYRNTrGEfYfGxSp+3jYL3PoNceIMkqM9haXjjGl0W1B4BidK1LVYBNov0rTEzyr0a1riUrp Qk+6z/LHxCM9lFFXnqH7KWeToTOPQebD2B/Ah5CZlft41i8L6LOF/LCuDBuYlu/fI2nuCc8d m4wwtkou1Y/kIwbEsE/6RQwRXUZhzO6llfoN96Fczr/RwvPIK5SVMixqWq4QGFAyK0m/1ap4 bhIRrdCLVQcgU4glo17vqfEaRcTW5SgX+pGs4KIPPBE5J/ABD6pBnUUAEQEAAcLA/AQYAQgA JhYhBIUq/WFSDTiOvUIqv2u9DlcdrjdRBQJlD89ZBQkFo5qAAhsMAAoJEGu9DlcdrjdR4C0L /RcjolEjoZW8VsyxWtXazQPnaRvzZ4vhmGOsCPr2BPtMlSwDzTlri8BBG1/3t/DNK4JLuwEj OAIE3fkkm+UG4Kjud6aNeraDI52DRVCSx6xff3bjmJsJJMb12mWglN6LjdF6K+PE+OTJUh2F dOhslN5C2kgl0dvUuevwMgQF3IljLmi/6APKYJHjkJpu1E6luZec/lRbetHuNFtbh3xgFIJx 2RpgVDP4xB3f8r0I+y6ua+p7fgOjDLyoFjubRGed0Be45JJQEn7A3CSb6Xu7NYobnxfkwAGZ Q81a2XtvNS7Aj6NWVoOQB5KbM4yosO5+Me1V1SkX2jlnn26JPEvbV3KRFcwV5RnDxm4OQTSk PYbAkjBbm+tuJ/Sm+5Yp5T/BnKz21FoCS8uvTiziHj2H7Cuekn6F8EYhegONm+RVg3vikOpn gao85i4HwQTK9/D1wgJIQkdwWXVMZ6q/OALaBp82vQ2U9sjTyFXgDjglgh00VRAHP7u1Rcu4 l75w1xInsg== In-Reply-To: <5529aa92-191d-4120-a005-28fe5c209a4f@zytor.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 6/23/2025 9:57 PM, Xin Li wrote: > On 6/23/2025 7:04 PM, H. Peter Anvin wrote: >> On June 23, 2025 10:40:59 AM PDT, Xin Li wrote: >>> On 6/20/2025 5:50 PM, H. Peter Anvin wrote: >>>> On 2025-06-20 17:45, H. Peter Anvin wrote: >>>>>> >>>>>> But I simply hate adding a disabled feature that depends on !X86_64; >>>>>> x86_64 has a broad scope, and new CPU features are often >>>>>> intentionally >>>>>> not enabled for 32-bit. >>>>>> >>>>>> (X86_DISABLED_FEATURE_PCID is the only one before LASS) >>>>> >>>>> More importantly, it is wrong. >>>>> >>>>> The 32-bit build can depend on this feature not existing, therefore >>>>> it SHOULD be listed as a disabled feature. >>>>> >>>> >>>> Ok, that was word salad. What I meant was that the original patch is >>>> correct, and we SHOULD have this as a disabled feature. >>> >>> Agreed! >>> >>>> The reason is that it reduces the need to explicitly test for 32/64 >>>> bits for features that don't exist on 32 bits. When they are flagged >>>> as disabled, they get filtered out *at compile time*. >>> >>> It's better to make it depend on X86_32 directly rather than !X86_64: >>> >>> config X86_DISABLED_FEATURE_LASS >>>     def_bool y >>>     depends on X86_32 >>> >>> >>> But the disabled feature list due to lack of 32-bit enabling will keep >>> growing until we remove 32-bit kernel code. >>> >>> Wondering should we bother enforcing cpuid_deps[] on 32-bit? >>> >>> IOW, turn off the feature when its dependency isn’t satisfied on 32b-it; >>> don’t just throw a warning and hope for the best. >>> >>> Thanks! >>>     Xin >>> >> >> We should have the dependencies enforced; in fact, preferably we would >> enforce them at build time as well. >> >> > > Yeah, sounds something we can do later :) > We could introduce a new Kconfig file at arch/x86/Kconfig.cpufeatures.disabled_on_32bit to track all features disabled due to lack of 32-bit support.