From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f74.google.com (mail-wm1-f74.google.com [209.85.128.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 303D32AD13 for ; Mon, 10 Nov 2025 12:15:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.74 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762776950; cv=none; b=lfE0wyuFsepzNK3AgYtYX2aTnaeUj6HU7QTZnRZpaYn47sv9NY4uE4eOhX0IDNnoLeZYplnHBrk2ysLHJda66LlXEWnU5PNkuDbIM3vkQsBhcTEbzHjiqFUzHRfFN2ddkx+e5aJJpewXABjcklsO+ThjfxABe1dXVAWtBAgRTnY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762776950; c=relaxed/simple; bh=L8BGqbB9mXhb9QhA+8Y/ns6WcRXrqxhhNfU7v+/1kic=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=uYXbpw95l3Abg+6XCoP59OQNbyZ+Ca0CSVdxGIWmiEwfzFZNQzIVFjebsIAIneB7BAVzx8l+/vd3EuUGtNXNO8GgTCxsp+BX2xX5QwHg5pIO8BeyqcXc5k5Co64XOSW5acBzxNMg6Zve2bTIPqHghZeUPHg8ogR1wzz7ZMKAdoU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--jackmanb.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=PzPvevk7; arc=none smtp.client-ip=209.85.128.74 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--jackmanb.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="PzPvevk7" Received: by mail-wm1-f74.google.com with SMTP id 5b1f17b1804b1-4774836c376so15475235e9.2 for ; Mon, 10 Nov 2025 04:15:47 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1762776946; x=1763381746; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=r7u+CaWniXfNbRMSrnjLhAt9t/fpHXv3Sd1ZHtazOKg=; b=PzPvevk79S2oToraIX60BlNisqSaAiE/G92DQsq8e3Mu8BtBCLx5NEsTmGTBXBhRfb REd/B9sBMFmLhC5iLqyN/I/3/VQU0aWOWRoGE3iAzUGolPNeMF7A+x8XKN5DWd0Dl90g lFI17tLrFD9q4myYt10riVZEuDsrRv7LnmS0B56VF3ZpV4X+MPceGq9eU6OWQTCqdpoz GzlCuN8hDX7mIjA1xB6F8qYmqwT9Z2AaPpqNoakg6wUmQk4+ln/SzElJvQvrZ+Zd5D1Q VVeCScgpiQO0DtlMj3GzJbh0m56Q9v+1llGjtgrWBfcYtu1LzK6tldaxcpGL/+S9o6K/ JzvQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1762776946; x=1763381746; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=r7u+CaWniXfNbRMSrnjLhAt9t/fpHXv3Sd1ZHtazOKg=; b=vYC2E907H+8CWp5Qmb5y2uwoLdkMHxmb70zP8ZmdSfSeD2FWjAAt9WnOD5hwSit6vY wuQNyZqAC17/7XrazFNUovmVc/OEhB3HAdfugimGXZEtuYarXiGXTuyCn/03mYfMPlQT 0YRYX5jsxfVE7P2r/omFNUnjL5RDCeTdYiQTOnggJAUup13N5J6Ooaujf8dqi8VHnt9X vFJUPHQhiERVCX8vRPCEnEnkrja/IrLq0HrE/XX54JNAZaYk7wTd8nzpeIj9p3x+nOhk p7fXvbqbPoMdrUtzuJ6kFav9pDfsLDhc568d0Gnl0qGmjQJ589g37t6tXArMJfImAhr2 Rw0w== X-Forwarded-Encrypted: i=1; AJvYcCUPIXgPMMlnAjr/ytbok6vfVZKLYNWU61RC8zKxo6VFcJ/xDRuJM50XQWE0HfqlCNdSwXqaF7//DddloVY=@vger.kernel.org X-Gm-Message-State: AOJu0YypDxbbDevjD5CJqHfIyGzT/26Ch8qcDbLE+1C6xNG2Q+wpu6BQ vmKuUgimfqIDtdJ6UOpLPkyIe87RELenRQeORuqZLj6KF+NxrySjlcFw0992Gj+WOkh7BSNVV7T e9Stf5JPXJLdSfw== 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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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" 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.