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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8B43FCA0EE6 for ; Fri, 15 Aug 2025 09:00:15 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 2F109900225; Fri, 15 Aug 2025 05:00:15 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2A2778E0002; Fri, 15 Aug 2025 05:00:15 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1BA3E900225; Fri, 15 Aug 2025 05:00:15 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 088078E0002 for ; Fri, 15 Aug 2025 05:00:15 -0400 (EDT) Received: from smtpin14.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id BC4FF83A12 for ; Fri, 15 Aug 2025 09:00:14 +0000 (UTC) X-FDA: 83778395148.14.ADD406D Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf11.hostedemail.com (Postfix) with ESMTP id 1B25040005 for ; Fri, 15 Aug 2025 09:00:12 +0000 (UTC) Authentication-Results: imf11.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf11.hostedemail.com: domain of kevin.brodsky@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=kevin.brodsky@arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1755248413; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=XU5bu+lKKeDLR9H4YP964In4FuB9GNE60ZYvTs3tXww=; b=hqyFkj8n/v/l/+Y6nb4epVeIGAY8j94qXs9ujOvg+5WffGRzS10icWDQvv6W8ThXUd1TX3 FhWb6o0rM0PE295tFToCpLIVcTTq9CfsaUDKBSR4XVFhG1jz4LGrwp61IXw6TV9007DgzL 9GK9wYW1AdTSsDgdOT+m0SLO4l8NfWA= ARC-Authentication-Results: i=1; imf11.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf11.hostedemail.com: domain of kevin.brodsky@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=kevin.brodsky@arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1755248413; a=rsa-sha256; cv=none; b=TqJO0+eQRzrlP78HE3QdkmcIk5wAkGCz3pydfYHL3zx3otyotgjAfv4kg8kBhUuBYPrbSZ 1BilSMSGJH5vMAZb+8OJDXoXLFh3in1eKiH01ikuQCUcK7gLqVw7sgtfdrI422zFtAz1rU kIBLyexu1+S+lVCBvMankNELmRvHjw0= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 18FDD1E32; Fri, 15 Aug 2025 02:00:04 -0700 (PDT) Received: from e123572-lin.arm.com (e123572-lin.cambridge.arm.com [10.1.194.54]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D38593F63F; Fri, 15 Aug 2025 02:00:07 -0700 (PDT) From: Kevin Brodsky To: linux-hardening@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Kevin Brodsky , Andrew Morton , Andy Lutomirski , Catalin Marinas , Dave Hansen , David Howells , "Eric W. Biederman" , Jann Horn , Jeff Xu , Joey Gouly , Kees Cook , Linus Walleij , Lorenzo Stoakes , Marc Zyngier , Mark Brown , Matthew Wilcox , Maxwell Bland , "Mike Rapoport (IBM)" , Peter Zijlstra , Pierre Langlois , Quentin Perret , Ryan Roberts , Thomas Gleixner , Vlastimil Babka , Will Deacon , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, x86@kernel.org Subject: [RFC PATCH v2 1/8] arm64: kpkeys: Avoid unnecessary writes to POR_EL1 Date: Fri, 15 Aug 2025 09:59:53 +0100 Message-ID: <20250815090000.2182450-2-kevin.brodsky@arm.com> X-Mailer: git-send-email 2.47.0 In-Reply-To: <20250815090000.2182450-1-kevin.brodsky@arm.com> References: <20250815090000.2182450-1-kevin.brodsky@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 1B25040005 X-Stat-Signature: 818ci65zbxqn18gnahizm73pt96gr8pj X-Rspam-User: X-HE-Tag: 1755248412-54517 X-HE-Meta: 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 gwSblAr4 IdhdalKkLYceCyfq6puKO/+E+v0sdlopPy8qOudDo0d4IXfFP+gdmZpldGsIea0EccfzwlrikhqHYQoRjYp5gcUqhPuJYJhY8zRAzFIOq/FvE35OKChYVU5B37DsXiPrFbpEeatcULVmFPbbdRT0Kx3KSVZKnvrlO6KU6W7ExSVhDuQpF7riN2pGZNJMyUWEj2PLpJABNxiHPlXU= 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: Nested uses of kpkeys guards are about to be introduced, which means that kpkeys_set_level() may not actually need to change the value of POR_EL1. Since updating POR_EL1 requires an expensive ISB, let's skip the write if the value is unchanged, by returning KPKEYS_PKEY_REG_INVAL. This will cause the matching kpkeys_restore_pkey_reg() call to bail out without calling arch_kpkeys_restore_pkey_reg(). Signed-off-by: Kevin Brodsky --- arch/arm64/include/asm/kpkeys.h | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/arm64/include/asm/kpkeys.h b/arch/arm64/include/asm/kpkeys.h index 64d6e22740ec..70e21df84252 100644 --- a/arch/arm64/include/asm/kpkeys.h +++ b/arch/arm64/include/asm/kpkeys.h @@ -43,6 +43,9 @@ static __always_inline int arch_kpkeys_set_level(int level) u64 prev_por = read_sysreg_s(SYS_POR_EL1); u64 new_por = por_set_kpkeys_level(prev_por, level); + if (new_por == prev_por) + return KPKEYS_PKEY_REG_INVAL; + __kpkeys_set_pkey_reg_nosync(new_por); isb(); -- 2.47.0