From patchwork Fri Apr 4 17:44:35 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Rutland X-Patchwork-Id: 14038731 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 83911C369A1 for ; Fri, 4 Apr 2025 18:12:54 +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-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-Id:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=o/Cs8lYUGOH5SnjCmGX9zMXwzw+sPq2MDvbljJYlujY=; b=jaZntEwbrst2kux1RR7QfdFcVR +wg3FIvOt/Id8erEnHRqfuhFQCStLCEAcoXlZqIfWl/cBKZG1qrhnvkna0mcBf2I6wbq8kT7WRTrz jc+PaMFyvDV+GPTBfhv/laRc6mHnVMyixSTgXl59D6YPakgAHzKLCC8LnbbzBz6ASQIC0FE4w+0xz H9DkOgVzcMk9mUAes4mLwOn+JZ+xVO4i1dqxzw5OZRMuNsBZRGgvn7Q8D5mSSC3VjK6GuIqHQVEj3 V5WjXJc9WFwLbEGipjOfTci3WL3RxA3HNLnXvMHHPZhaA8hIGKQ+k0f6aXcozl0Oq5cbnPdjSf/MV pVEXnXKg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.1 #2 (Red Hat Linux)) id 1u0lX3-0000000CV8C-0Vg8; Fri, 04 Apr 2025 18:12:45 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.1 #2 (Red Hat Linux)) id 1u0l6O-0000000CRUR-1kCt for linux-arm-kernel@lists.infradead.org; Fri, 04 Apr 2025 17:45:13 +0000 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 2BD661515; Fri, 4 Apr 2025 10:45:14 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id AB3EA3F63F; Fri, 4 Apr 2025 10:45:10 -0700 (PDT) From: Mark Rutland To: linux-arm-kernel@lists.infradead.org Cc: ardb@kernel.org, broonie@kernel.org, catalin.marinas@arm.com, mark.rutland@arm.com, maz@kernel.org, will@kernel.org Subject: [PATCH 14/14] arm64/fpsimd: signal: Simplify preserve_tpidr2_context() Date: Fri, 4 Apr 2025 18:44:35 +0100 Message-Id: <20250404174435.3288106-15-mark.rutland@arm.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20250404174435.3288106-1-mark.rutland@arm.com> References: <20250404174435.3288106-1-mark.rutland@arm.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250404_104512_503290_49721E22 X-CRM114-Status: UNSURE ( 9.65 ) X-CRM114-Notice: Please train this message. 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 During a context-switch, tls_thread_switch() reads and writes a task's thread_struct::tpidr2_el0 field. Other code shouldn't access this field for an active task, as such accesses would form a data-race with a concurrent context-switch. The usage in preserve_tpidr2_context() is suspicious, but benign as any race with a context switch will write the same value back to current->thread.tpidr2_el0. Make this clearer and match restore_tpidr2_context() by using a temporary variable instead, avoiding the (benign) data-race. Signed-off-by: Mark Rutland Cc: Catalin Marinas Cc: Marc Zyngier Cc: Mark Brown Cc: Will Deacon Reviewed-by: Mark Brown --- arch/arm64/kernel/signal.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c index b27357aeba065..a4e3d4273a360 100644 --- a/arch/arm64/kernel/signal.c +++ b/arch/arm64/kernel/signal.c @@ -476,13 +476,12 @@ extern int preserve_sve_context(void __user *ctx); static int preserve_tpidr2_context(struct tpidr2_context __user *ctx) { + u64 tpidr2_el0 = read_sysreg_s(SYS_TPIDR2_EL0); int err = 0; - current->thread.tpidr2_el0 = read_sysreg_s(SYS_TPIDR2_EL0); - __put_user_error(TPIDR2_MAGIC, &ctx->head.magic, err); __put_user_error(sizeof(*ctx), &ctx->head.size, err); - __put_user_error(current->thread.tpidr2_el0, &ctx->tpidr2, err); + __put_user_error(tpidr2_el0, &ctx->tpidr2, err); return err; }