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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; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: E1FDD16000D X-Stat-Signature: xgpmdssn1isrif6ux11qops5d5dyaec9 X-HE-Tag: 1750741921-542843 X-HE-Meta: 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 EF7P4kPW Rl52kfrX9+cmviyrDPKDAxbDPo12QwaftlgmNQ+I6PqdKV4Ttiu/ey2gxsgPU0RIWubfcTZph6ssKr0+Ush5hmVrCuqDW4Wx+uscQasay4Kp/ZB2Ql8To8ZFl7ieWfisGMRuDyQ6rQaoI1ad3iGk++bxJswCkqtPwgxzJh4efpXXrLr9OmaEG0UZ4juUJ8GkU6zS9mFstY3PGKmn8440saYrDU8hgBinMZamAMU7t5FYu/Ql4GBnBmvmzsd5qsN1ZecFL1cwrJNt64kOcHVQ0dI/n/SjtEKR3Kze1lwh1Gzl53Z+R5rccmSqVsDA47yQEfDCrs39Gpb8gD5T1T4AbOoM4z9RP1OIa/vSRq4E5fFjIzsTRQg/TwXX49S5rGiRC/EVVg4YMfvcK1Vif1r8kmDZG301IOGYJ+qr0SjDtjitsjKxgjgq/PTdU5h5WOicofWY0 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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.