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 A1850D29C36 for ; Mon, 19 Jan 2026 15:34:29 +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:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From: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=/qYf/PHQFWJCnIpSyFGqKWYMu6hZ8FKioOYMYzGdZY0=; b=Q/Y1UZAUtbRuFxo5D0AWkn2ob0 RIxdDOIkaA/y83hlz8YmLX4oZimcT1p1GENfeNWID8jmaCyJUv8m+c+hX38PtfqL680PiTYRl/N5W NjoUBxu6ZBNWckRbkm4elNKf0mF686IJ1RNGdmsz61HAU0ycaWUcnGYtG7Jgik2LHYYlT2WBcZPLw kQzIobrhNLn6sExYQLWI4os8/yzNgK7S/FQIuBm7K8EDAuDecdcGxw4qsgHlyXTE08xTQp1BKVRgA BFsm1k5AObKJI45irB8LDLanctF+9DydmW+SYBLsyaIOqtLvk+n533UqVloVrp9NAIFhd22F5AwNT DknHosow==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vhrGj-00000002MUF-2QNo; Mon, 19 Jan 2026 15:34:17 +0000 Received: from tor.source.kernel.org ([172.105.4.254]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vhrGh-00000002MU4-3PBI for linux-arm-kernel@lists.infradead.org; Mon, 19 Jan 2026 15:34:15 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id E946C600C3; Mon, 19 Jan 2026 15:34:14 +0000 (UTC) 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 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