From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 19FB81A3172; Mon, 19 Jan 2026 15:34:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768836855; cv=none; b=f0qqTFRpZWSiLa7vv8Id3DdetFygQk9i2rPSZj6Y/o4kbVwB0WZwE3w2C4eRXIJnx4t4ZjGrD5FLN6jc0IRUIHd/dj12C/GPo9S6Z0a8IQcB6qcC4BplTd8Wm/DPHG1kS1GT+ixIdqpCkAWhmuCJd9LNm0w5EitUECqYJzLYZpo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768836855; c=relaxed/simple; bh=EV9T2myKyHW3Va2uCiNnqCvAhEhltNmAw8tpzkkdAzE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=j0b89vzcTsc0LtnG1/6tXNJKLcbqt3wH2DvX2zHQ67yLTjrzhhB67KohcItqTzdJhsXKQXnRD2pctSIGyANls2drpe/76xnh/6KPFZviSZePZzXMFGJBwPTy7MzwFqqUpgNscTcGTZ31JL/K5fVLp72FCXT4ZEtcqmChFwPfCn0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=hnTPBamt; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="hnTPBamt" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6981CC116C6; Mon, 19 Jan 2026 15:34:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768836854; bh=EV9T2myKyHW3Va2uCiNnqCvAhEhltNmAw8tpzkkdAzE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=hnTPBamtcpdz1LcA6KzmSTKkAZ+TFdl7qyRNKWE3Akp48IOYXqvoOqmcFIyjLmtcA j8slHUynBdR7vCN2o5vdKzJJ+AJPt2faLJ7NDN9kmc9vEUgolojkGLCFHaiaM8DGuy ayds765ZMJhLuH/0dSdeAPclWKXpdn/ehgC1SI3hNTv5WrpcA59Shg2UVKLtjNiadm 3dnm61SJHT4FfTqP/Z6CuaT9OqoAvL95U62K2ZA0FlZNfEPAR9iEkfm1YIoieddOeO r6fBFs3NruE+FS+bG+MFkqIqDe47vIrXlGpGOlIKd9ZSmW1mpyAJPmYXEWOH+1RsVQ g96pudsYi2RCQ== Date: Mon, 19 Jan 2026 15:34:07 +0000 From: Will Deacon To: Yeoreum Yun Cc: Marc Zyngier , catalin.marinas@arm.com, broonie@kernel.org, oliver.upton@linux.dev, miko.lenczewski@arm.com, kevin.brodsky@arm.com, ardb@kernel.org, suzuki.poulose@arm.com, lpieralisi@kernel.org, yangyicong@hisilicon.com, scott@os.amperecomputing.com, joey.gouly@arm.com, yuzenghui@huawei.com, pbonzini@redhat.com, shuah@kernel.org, mark.rutland@arm.com, arnd@arndb.de, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v11 RESEND 9/9] arm64: armv8_deprecated: apply FEAT_LSUI for swpX emulation. Message-ID: References: <20251214112248.901769-1-yeoreum.yun@arm.com> <20251214112248.901769-10-yeoreum.yun@arm.com> <86ms3knl6s.wl-maz@kernel.org> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Dec 15, 2025 at 09:56:04AM +0000, Yeoreum Yun wrote: > Hi, > > > On Sun, 14 Dec 2025 11:22:48 +0000, > > Yeoreum Yun wrote: > > > > > > Apply the FEAT_LSUI instruction to emulate the deprecated swpX > > > instruction, so that toggling of the PSTATE.PAN bit can be removed when > > > LSUI-related instructions are used. > > > > > > Signed-off-by: Yeoreum Yun > > > > It really begs the question: what are the odds of ever seeing a CPU > > that implements both LSUI and AArch32? > > > > This seems extremely unlikely to me. > > Well, I'm not sure how many CPU will have > both ID_AA64PFR0_EL1.EL0 bit as 0b0010 and FEAT_LSUI > (except FVP currently) -- at least the CPU what I saw, > most of them set ID_AA64PFR0_EL1.EL0 as 0b0010. Just to make sure I understand you, you're saying that you have seen a real CPU that implements both 32-bit EL0 *and* FEAT_LSUI? > If you this seems useless, I don't have any strong comments > whether drop patches related to deprecated swp instruction parts > (patch 8-9 only) or not. > (But, I hope to pass this decision to maintaining perspective...) I think it depends on whether or not the hardware exists. Marc thinks that it's extremely unlikely whereas you appear to have seen some (but please confirm). Will