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 6071AC433FE for ; Fri, 8 Apr 2022 18:41:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=ZsUS50shuDl6UlfzXwVDRRD3sDUZVjECce6RD2EF+bc=; b=fcza48aIyNOZV7 MOibEQngloFz6MsMDVnpuaIXV5uzB+ir/YG9tZRaPdUCczAjFCWZ8qWv7LW1Koxe85Wd9HBO+qh31 CnAIgNOwWcL56LWLd8hDamM1GD8QT+rgZBBIjCg13XoVqTr5ZDgM4XGVvHVXiTPbaFGFL3EYsi9Ep v4IxLYKjFWEV8JKRghB0X2qYtj17PvXhYymCeaS7d0lGLe7RM3HBtC4ElQj3P0EVcjKzX0PunEFoC sKgmYkBq4/ibRW7NkpA1CRyD7ifDN00MoiKtYpT8zaaakd/PW414XyZvmnNl0EWm+/4zy5KYfGpR/ so1DQI2x8CTZqEl1gpVw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nctX0-000zD4-On; Fri, 08 Apr 2022 18:40:26 +0000 Received: from dfw.source.kernel.org ([139.178.84.217]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nctWx-000zC2-Ss; Fri, 08 Apr 2022 18:40:25 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 6810760B21; Fri, 8 Apr 2022 18:40:23 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 37DAEC385A3; Fri, 8 Apr 2022 18:40:19 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="hw7ZM3DK" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1649443217; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=5p8HbWxOv/2pCcrFRIk5uy5GvnZxVWWqGCXEJeAr/VI=; b=hw7ZM3DKXNV/PCbZ27tOsMmXRTiv/fRiwXtCpNB0Y95WzzR8bK+prKfASznhrt+sI6VYcP JgT9H5GtkoA+jROggAq+JYownqGfREZ8MSGOuZKcJzf+CHaADipObRJFEs60xwyHJ1+hny xsJ6FQ5svtLEpIhYOh3ZMRBXxb2C+BU= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 6baee431 (TLSv1.3:AEAD-AES256-GCM-SHA384:256:NO); Fri, 8 Apr 2022 18:40:17 +0000 (UTC) Date: Fri, 8 Apr 2022 20:40:08 +0200 From: "Jason A. Donenfeld" To: Mark Rutland Cc: linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, arnd@arndb.de, Theodore Ts'o , Dominik Brodowski , Russell King , Catalin Marinas , Will Deacon , Geert Uytterhoeven , Thomas Bogendoerfer , Paul Walmsley , Palmer Dabbelt , Albert Ou , "David S . Miller" , Richard Weinberger , Anton Ivanov , Johannes Berg , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H . Peter Anvin" , Chris Zankel , Max Filippov , John Stultz , Stephen Boyd , linux-arm-kernel@lists.infradead.org, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-riscv@lists.infradead.org, sparclinux@vger.kernel.org, linux-um@lists.infradead.org, x86@kernel.org, linux-xtensa@linux-xtensa.org Subject: Re: [PATCH RFC v1 07/10] arm64: use sched_clock() for random_get_entropy() instead of zero Message-ID: References: <20220408182145.142506-1-Jason@zx2c4.com> <20220408182145.142506-8-Jason@zx2c4.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220408_114024_045742_42DBD98A X-CRM114-Status: GOOD ( 23.30 ) 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: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Mark, On Fri, Apr 08, 2022 at 07:33:53PM +0100, Mark Rutland wrote: > On Fri, Apr 08, 2022 at 08:21:42PM +0200, Jason A. Donenfeld wrote: > > In the event that random_get_entropy() can't access a cycle counter or > > similar, falling back to returning 0 is really not the best we can do. > > Instead, at least calling sched_clock() would be preferable, because > > that always needs to return _something_, even falling back to jiffies > > eventually. It's not as though sched_clock() is super high precision or > > guaranteed to be entropic, but basically anything that's not zero all > > the time is better than returning zero all the time. > > > > If CONFIG_ARM_ARCH_TIMER=n, then get_cycles() will return 0, so we only > > need the fallback code for that case. > > In arch/arm64/Kconfig we unconditionally select CONFIG_ARM_ARCH_TIMER, > so that configuration shouldn't be possible, and I don't think this > patch is necessary. > > On arm64 we depend on the architected timer in a bunch of places, so > anyone hacking that out has bigger problems. Thanks for the tip. I'll drop this patch from the series. Jason _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel