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Peter Anvin" To: Xin Li , "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, Yian Chen Subject: Re: [PATCHv6 01/16] x86/cpu: Enumerate the LASS feature bits User-Agent: K-9 Mail for Android In-Reply-To: <73796800-819b-4433-b0ef-db852336d7a4@zytor.com> References: <20250620135325.3300848-1-kirill.shutemov@linux.intel.com> <20250620135325.3300848-2-kirill.shutemov@linux.intel.com> <73796800-819b-4433-b0ef-db852336d7a4@zytor.com> Message-ID: <0A71C898-B587-4292-AB05-6CA46BBD6F88@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 9AFF21C000B X-Stat-Signature: 9izkrwepmwd8f5shu31wmsfx8bfkra61 X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1750730686-164324 X-HE-Meta: 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 HEBfO9Iy Wqg8EQJSDK/2YDfRI5H8VdD6NB7DPJ/isirL3/BI1PVHr9OKogsABYfWgBszKYhySjFaF 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 June 23, 2025 10:40:59 AM PDT, Xin Li wrote: >On 6/20/2025 5:50 PM, H=2E Peter Anvin wrote: >> On 2025-06-20 17:45, H=2E Peter Anvin wrote: >>>>=20 >>>> 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 intentionall= y >>>> not enabled for 32-bit=2E >>>>=20 >>>> (X86_DISABLED_FEATURE_PCID is the only one before LASS) >>>=20 >>> More importantly, it is wrong=2E >>>=20 >>> The 32-bit build can depend on this feature not existing, therefore it= SHOULD be listed as a disabled feature=2E >>>=20 >>=20 >> Ok, that was word salad=2E What I meant was that the original patch is = correct, and we SHOULD have this as a disabled feature=2E > >Agreed! > >> The reason is that it reduces the need to explicitly test for 32/64 bit= s for features that don't exist on 32 bits=2E When they are flagged as disa= bled, they get filtered out *at compile time*=2E > >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=2E > >Wondering should we bother enforcing cpuid_deps[] on 32-bit? > >IOW, turn off the feature when its dependency isn=E2=80=99t satisfied on = 32b-it; >don=E2=80=99t just throw a warning and hope for the best=2E > >Thanks! > Xin > We should have the dependencies enforced; in fact, preferably we would enf= orce them at build time as well=2E