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AJvYcCVzXMf94bm8O8bGWICFRijrFK+bCyFY/i428q3l7eAV1mgCEm+l/aVr0qYmSlbwdkFXzBwistsurg==@kvack.org X-Gm-Message-State: AOJu0YzfB1N+LykOlFRGMl0jwRQor1Tb2cZ0MRGHWiTXR3GUzsF/gqs7 JcGgpZgbNx/TvZ6CrDggraszwcYm0Z3PEgrCCGs0IfoEwI5KZkmdS2npIaGVW+h4ZleJDTVoifZ aIVOex71HXz/toQ== X-Google-Smtp-Source: AGHT+IFsVkAJqDrA0QC1vNQvIugx9gGlCHC4/kl3pctZZHSVNpuIB2x8+7Vb8XbTb0E+0lyCnqY/M4AHDRthJA== X-Received: from wmee11.prod.google.com ([2002:a05:600c:218b:b0:477:63d9:f561]) (user=jackmanb job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:1c15:b0:477:7c45:87b1 with SMTP id 5b1f17b1804b1-4777c45885amr34406585e9.36.1762776946520; Mon, 10 Nov 2025 04:15:46 -0800 (PST) Date: Mon, 10 Nov 2025 12:15:45 +0000 In-Reply-To: <20251110112640.GVaRHL8GME4ODowica@fat_crate.local> Mime-Version: 1.0 References: <20250924-b4-asi-page-alloc-v1-0-2d861768041f@google.com> <20250924-b4-asi-page-alloc-v1-2-2d861768041f@google.com> <20251025100642.GVaPyhMp4CEmsYW3xy@fat_crate.local> <20251110112640.GVaRHL8GME4ODowica@fat_crate.local> X-Mailer: aerc 0.21.0 Message-ID: Subject: Re: [PATCH 02/21] x86/mm/asi: add X86_FEATURE_ASI and asi= From: Brendan Jackman To: Borislav Petkov , Brendan Jackman Cc: Andy Lutomirski , Lorenzo Stoakes , "Liam R. Howlett" , Suren Baghdasaryan , Michal Hocko , Johannes Weiner , Zi Yan , Axel Rasmussen , Yuanchu Xie , Roman Gushchin , , , , , , , , , , , , , , , , Yosry Ahmed Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam12 X-Rspam-User: X-Rspamd-Queue-Id: 319841C0005 X-Stat-Signature: bnu56kimyt37jbatenupn85xywck34z3 X-HE-Tag: 1762776947-668754 X-HE-Meta: U2FsdGVkX1/UZQ3IGfCn/Ii9eULgbe9/BhB9Ae6IlEXM2edmlla0daB/OR1G1ye+4pNS/siGu3Ybqxy8hnB12y+/+BwVfo8DkUzqm43JqzRMBJ74BPW8KFkDAprlaagQDvTU2s1HC3v/oSziCw4WYEHoQLfnsbIhAaKXlkFciVuRfJ2N8cjYMFebArE0vONHFXRmsrUfzA7XoNkCqntURH39oJ519gI/rC1xjDZKj8r5hKvihJRAlx6jfz49hCBFDD867DckegBFBQJCZbpeRZgoUDi9ybkKEodTcZuSYIXlFZKNMpfT5ONxAo/xoNhc1CAI+dK0T0uW/K4NXlQm/+gFUyaSUxsIAsKUmFepcX75djNO950PYG/fRVK5fC2obLUR6mihFfQ3crqhu6PdaDAGtioQaWe/7Fgf2inEE8pU7h0+fbwlDsjJacPVwOkmQQFusVw3NjPoDlE+Qc5hDX6FUGWmrGOwtJjjuB0f5anxtcqCmnITGK29MHMArTsByGYUXg3Fbzv6yXkOgXzcGrseRCXUfnI2W+fCNE8sf3vRIyKdYLrKvIsvMUNbnDz1IHcgjeIE/sBimZGLRgojTTWf27U5X5+sGS0yDrAYCI5INRAuivxbhPNBqUFDK8F/TNVxZFO6tjn7YpmRc7wN7Y9PjjaoTeQ7erupOlLJBNAM/7FeCVu2lwvkTp6p3dA42wmMQRStj2b3S0fnOMuNP+N+MBVXcBESn1PF9GPhG7BCt8sEiAErOAG2uVI1Dewe9aGU4/A03SmCe8ejCJbZprrnpcfbPmXCv3wLzD7M+UVcy9gM9B2akeyMQ6iiJmii2UnKNiTfl2b4LdsAXcq87a+Ah8eW4dPxwg9MVoD2SLAXs6rBqyqPbpKg9yKBY88vpR8fDhMdKa88cJioBSFKdmUOwMbNOJjEdkIhS+nUybBy1tc1npjm4frgWYOcfGqKG1lWhpzarURia6siifa pbi+NDb6 DEviRkjUjfu0hXoG5s0GiF27WCjqdgYK5Byb47N6ODwZ/GbaBEcjfmI/DWhVYFyDSS78wN1QGC6rMJGVcag6kZLmhrykMPXDycPn8OzmyhSOnB6IxuiduD8KJK871TJ50Y7OF+2hgmuc7taTk4MwT+mFdQ/+6js3sg+kRmgiaBEJppQ9slqzWbAerHN0j1sKh3O7A2Od23xk7zRW1XJNvS8PdqOi/RrC+6eq1ip0wnelxGC9OXCW0iNlA+iPkLmltcvCZ4O4R5LqtKJi1EB8HlNGnI49Ia/2RpXxDbBqLz5din/mEqk3K7o/RiM7DZ6PxolqQ7fxZjz4xpq9ATj4XzJL9Qx/cgLMSO4pcoE2BzYKVi+g3JKBmmBR81yyTvN/cXXJZ+pPWY5AMFnW0XIId2JVfvtYdrNfht5NxOBybHqpDYYUOBB/tVUD7Xg== 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 Mon Nov 10, 2025 at 11:26 AM UTC, Borislav Petkov wrote: > On Sun, Oct 26, 2025 at 10:24:35PM +0000, Brendan Jackman wrote: >> Hm yeah, I actually also thought I had some direct feedback from one of >> the x86 maintainers saying not to expose it here. I can no longer find >> that feedback on Lore so I think I must be misremembering, the flag >> was already hidden back in [0]. >> >> [0] https://lore.kernel.org/linux-mm/20240712-asi-rfc-24-v1-5-144b319a40d8@google.com/ >> >> If that feedback indeed doesn't exist > > Just ignore everything whoever might've told you or not - we override all > previous statements! :-P > > From Documentation/arch/x86/cpuinfo.rst > > "So, the current use of /proc/cpuinfo is to show features which the > kernel has *enabled* and *supports*. As in: the CPUID feature flag is > there, there's an additional setup which the kernel has done while > booting and the functionality is ready to use. A perfect example for > that is "user_shstk" where additional code enablement is present in the > kernel to support shadow stack for user programs." > > So it is all written down now and is the law! :-P > >> then personally I'd lean towards exposing it right away, I don't see that >> much downside in terms of ABI, since ASI kinda "doesn't do anything", from >> a SW point of view it's just a very weird and complicated NOP. It's hard for >> me to see how userspace could grow a functional dependency on this flag. >> Whereas for general monitoring it's handy. > > The point is: once all the ASI code lands, we should show it in cpuinfo. As > in: "this kernel supports ASI" and not "there's asi in cpuinfo but well, > that's not the whole deal." > > Makes sense? Sure, sounds good to me.