From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 33B83E9A03B for ; Thu, 19 Feb 2026 08:52:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Type:MIME-Version: References:In-Reply-To:Subject:Cc:To:From:Message-ID:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=UZxkxblp6TixMEwIaGTDp7E9JHHMSqbD/Krw5trN9/E=; b=Zkgzhm7LFzsg1DMZDep2SII3BC AUxcDAl6ui24OUoBwx/uapmEmxXWxy8Ch3MEf7LqUdt7G18AEq9d0ttiIXepg4x+uohAyJK6mZJc7 8Ey6Jjv2uyUfLGqqExnq38ME+YntyR9JRSAHcCqa6ou32feJ/nucMz8fybI4K5lYXnjm9icmP05uK /sZImrEbj35DKU216j8PWaZ6wNPG+vr02y1iAohLo84lsfFFDv6fp7G4R6ijOFNPq31aXE+4g1F0i s4KmTQyT8NdPaL2L0AyxrjAl+kiS+bi6mA9k/wOprQuR4o5sq1roq2x1I/svEg5BHpk0csVZHM4PE +dgmEllA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vszm5-0000000B8md-45gN; Thu, 19 Feb 2026 08:52:41 +0000 Received: from sea.source.kernel.org ([172.234.252.31]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vszm4-0000000B8mI-0Cki for linux-arm-kernel@lists.infradead.org; Thu, 19 Feb 2026 08:52:41 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 76ABF44400; Thu, 19 Feb 2026 08:52:39 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 54C8FC4CEF7; Thu, 19 Feb 2026 08:52:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771491159; bh=v061NrNSwWbxE0RIDyv/Yxf/o9/3zvP9EnRFRZFcJkk=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=rOgVvqX/IVX2XkJmI3F9tVNkUwdwh/eJMer1pW3UfEG7QrOSbBoLPmF8p7su0ccOw wO21fzXI9523wzPDl9ZYOsuCv9ss2A4oc16n56DTn8LguNa7iF60tFUVv/WZAvEvfF WVXfZ8YYG8emiLgIXw5z8mGSeRW2vVkJ9orGMSubGNG2rpayaK6Q1IQGOWclQXo3gg VhWi9jPDuHiYI2p/ahHV0IbPghE3amBvOxPOXYHNw7tlKX9NGNhUx8gllU/Th4oo8L WnZdKs+bjRMfGKhP9b5N8cEzJg5QXRzxYSBQEmMIQFDZQzDJ8HyZySShJnvhnSinR6 KlHZoPcWBxK8Q== Received: from sofa.misterjones.org ([185.219.108.64] helo=goblin-girl.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.98.2) (envelope-from ) id 1vszm1-0000000C5gz-0I2B; Thu, 19 Feb 2026 08:52:37 +0000 Date: Thu, 19 Feb 2026 08:52:36 +0000 Message-ID: <86y0kp9ktn.wl-maz@kernel.org> From: Marc Zyngier To: Manoj Ekbote Cc: "linux-arm-kernel@lists.infradead.org" Subject: Re: FEAT_CMOW In-Reply-To: References: User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/30.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: mekbote@qti.qualcomm.com, linux-arm-kernel@lists.infradead.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260219_005240_110006_F523945F X-CRM114-Status: GOOD ( 20.25 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, 19 Feb 2026 05:21:02 +0000, Manoj Ekbote wrote: > > Hi, > > While looking at the mainline v6.18.6 sources, I noticed that > FEAT_CMOW does not appear in the arm64 CPU capability table > (arch/arm64/kernel/cpufeature.c). Since CMOW is a mandatory > architectural feature starting in Arm v8.8, I expected to see it in > the cpufeature framework. How is the cpu feature list typically > updated for architectural extensions like this? When we have a use for it. FEAT_CMOW has the potential to break the ABI we already expose to userspace, so I don't immediately see why we'd care about it. > Is it done only when the kernel needs to make use of the feature, or > is there a process to actively add all mandatory architecture > features? The Linux kernel is thankfully not a validation tool for the architecture, and is not aligned to any particular version of the architecture either. A "mandatory" feature is only a requirement for implementations, not for SW. Thanks, M. -- Without deviation from the norm, progress is not possible.