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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 16C46C433EF for ; Fri, 27 May 2022 11:49:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1352025AbiE0Ltf (ORCPT ); Fri, 27 May 2022 07:49:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56538 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1352232AbiE0Lpf (ORCPT ); Fri, 27 May 2022 07:45:35 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C6CA814641E; Fri, 27 May 2022 04:42:15 -0700 (PDT) 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 14B8E61CDB; Fri, 27 May 2022 11:42:15 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 20321C385A9; Fri, 27 May 2022 11:42:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1653651734; bh=Af/mC/zq4tKhaB0LwhH5Vk0R8nnqO8wO9ms7HejQAZU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=pD7bvtrPlS8ERDSZdLnMF1C9HtNY1paDKTXP8kQC3kSr+1h23VSWODCAXYJ4VF2cn EqFqQXeQ5L5nOguwHk16ogaJW4k36bpEzqgXj4wVnX1uULGHmlTRms8Dlz1uEXxEix vjl0yabrZINAziZkVc3+W60xvhGOJmhe9rDWxB70= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Thomas Gleixner , Arnd Bergmann , "Maciej W. Rozycki" , Thomas Bogendoerfer , "Jason A. Donenfeld" Subject: [PATCH 5.17 077/111] mips: use fallback for random_get_entropy() instead of just c0 random Date: Fri, 27 May 2022 10:49:49 +0200 Message-Id: <20220527084830.372270403@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220527084819.133490171@linuxfoundation.org> References: <20220527084819.133490171@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Jason A. Donenfeld" commit 1c99c6a7c3c599a68321b01b9ec243215ede5a68 upstream. For situations in which we don't have a c0 counter register available, we've been falling back to reading the c0 "random" register, which is usually bounded by the amount of TLB entries and changes every other cycle or so. This means it wraps extremely often. We can do better by combining this fast-changing counter with a potentially slower-changing counter from random_get_entropy_fallback() in the more significant bits. This commit combines the two, taking into account that the changing bits are in a different bit position depending on the CPU model. In addition, we previously were falling back to 0 for ancient CPUs that Linux does not support anyway; remove that dead path entirely. Cc: Thomas Gleixner Cc: Arnd Bergmann Tested-by: Maciej W. Rozycki Acked-by: Thomas Bogendoerfer Signed-off-by: Jason A. Donenfeld Signed-off-by: Greg Kroah-Hartman --- arch/mips/include/asm/timex.h | 17 ++++++++--------- 1 file changed, 8 insertions(+), 9 deletions(-) --- a/arch/mips/include/asm/timex.h +++ b/arch/mips/include/asm/timex.h @@ -76,25 +76,24 @@ static inline cycles_t get_cycles(void) else return 0; /* no usable counter */ } +#define get_cycles get_cycles /* * Like get_cycles - but where c0_count is not available we desperately * use c0_random in an attempt to get at least a little bit of entropy. - * - * R6000 and R6000A neither have a count register nor a random register. - * That leaves no entropy source in the CPU itself. */ static inline unsigned long random_get_entropy(void) { - unsigned int prid = read_c0_prid(); - unsigned int imp = prid & PRID_IMP_MASK; + unsigned int c0_random; - if (can_use_mips_counter(prid)) + if (can_use_mips_counter(read_c0_prid())) return read_c0_count(); - else if (likely(imp != PRID_IMP_R6000 && imp != PRID_IMP_R6000A)) - return read_c0_random(); + + if (cpu_has_3kex) + c0_random = (read_c0_random() >> 8) & 0x3f; else - return 0; /* no usable register */ + c0_random = read_c0_random() & 0x3f; + return (random_get_entropy_fallback() << 6) | (0x3f - c0_random); } #define random_get_entropy random_get_entropy