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 C3AD4C433EF for ; Mon, 11 Apr 2022 08:19:44 +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:MIME-Version:Message-ID:Date:References :In-Reply-To:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=nqXYQ/OHZpgSBMizwinYea3843S1Lw2elQ12U9+8Qxw=; b=KjGhOnvdFR+2Iw EF1vrgo+weuTl8z39Kqs+oGmN9+8r2Wz5Y/+KuOITbC370SPJDfzRRgbyYW9qaJQwflMU2t7WAWMb HFLHfb+PRrMzP3eC1jw16M4XDHtthQUi8nU53/KrAMH4mO7Gh4XRqpTvINCRo6mSIzwdpwzL15rVY mX96gC6GycP81ozWpg5Tc6CubLW2dyiIj8ShdGVp3n45PI3fg5DFNFiyZSWjVsElncoWNjWT8Yy+z 0hT8qRe/yADaCDODJBGre5oEw6CA+2XTHDgGx1fjYH2zYxYBjoiFWj/MaQawV58xlfbcl9QSyzqOP ED69uEn5rSvI96t3olHA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1ndpFr-007Ux3-Jt; Mon, 11 Apr 2022 08:18:35 +0000 Received: from galois.linutronix.de ([2a0a:51c0:0:12e:550::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1ndpFp-007Uvv-3s; Mon, 11 Apr 2022 08:18:34 +0000 From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1649665111; 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=xjhhzRNcm78JGgGtLG6mgwaGj8Cww0Tlt26NaB6GyE8=; b=bQRUSKc6DEfWq2JW4zBYVX9dk6BAlFAOz8ziZI1nuAr8ThUSn9e4Pp4TH0bz7ykDdAbytZ 7E1JFmxLLPSA9yL/pLdV+Narb8ojwoUuHfRpcDWF7RSs/XNw8NP/mtP12PhEDKsDgxWdwX vj1X7Tk9jubTJlEIAMDexIL70/zM+Ev13+w45xEIm/Pg10UwmbczcL33LQfaYjkFbjCAwR nWRv8uLzxf0uwY7wWrnhC9hKJv5hsVxGhFPLc//BILYIvle9sl9xbz+4/B2WaiAREmOlO7 QMeWCwYxU6fvIGepcveLrvpqjGJJ/UVr5H5Gu5FcUTDSJ2ZLo6XAuABFlQLZ3A== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1649665111; 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=xjhhzRNcm78JGgGtLG6mgwaGj8Cww0Tlt26NaB6GyE8=; b=dYt2Xa6X2UETGYKSaI3sFGG38t3wto/bY9ksZnmh+Jh5QgkWcPQfA5MzFrnWyF0a21HHlJ MeANaRegf0On2MDw== To: "Jason A. Donenfeld" , linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, arnd@arndb.de Cc: "Jason A. Donenfeld" , 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 , Ingo Molnar , Borislav Petkov , Dave Hansen , "H . Peter Anvin" , Chris Zankel , Max Filippov , John Stultz , Stephen Boyd , Dinh Nguyen , 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 v2 03/11] m68k: use ktime_read_raw_clock() for random_get_entropy() instead of zero In-Reply-To: <20220410214951.55294-4-Jason@zx2c4.com> References: <20220410214951.55294-1-Jason@zx2c4.com> <20220410214951.55294-4-Jason@zx2c4.com> Date: Mon, 11 Apr 2022 10:18:30 +0200 Message-ID: <87sfqkf2y1.ffs@tglx> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220411_011833_342042_B42B2C99 X-CRM114-Status: GOOD ( 22.20 ) 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 On Sun, Apr 10 2022 at 23:49, 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 ktime_read_raw_clock() would be preferable, > because that always needs to return _something_, even falling back to > jiffies eventually. It's not as though ktime_read_raw_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. > > Cc: Thomas Gleixner > Cc: Arnd Bergmann > Cc: Geert Uytterhoeven > Signed-off-by: Jason A. Donenfeld > --- > arch/m68k/include/asm/timex.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/m68k/include/asm/timex.h b/arch/m68k/include/asm/timex.h > index 6a21d9358280..5351b10e1b18 100644 > --- a/arch/m68k/include/asm/timex.h > +++ b/arch/m68k/include/asm/timex.h > @@ -35,7 +35,7 @@ static inline unsigned long random_get_entropy(void) > { > if (mach_random_get_entropy) > return mach_random_get_entropy(); > - return 0; > + return ktime_read_raw_clock(); I'd rather do something like this in a common header: unsigned long random_get_entropy_fallback(void); and use random_get_entropy_fallback() in the architecture specific files. That way you can encapsulate the fallback implementation in the random code and if it turns out that ktime_read_raw_clock() is a stupid idea or someone has a better idea then you have to change exactly one place and not patch the whole tree again. Thanks, tglx _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel