From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753576AbeDYVrD (ORCPT ); Wed, 25 Apr 2018 17:47:03 -0400 Received: from mail.kernel.org ([198.145.29.99]:36346 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751563AbeDYVq4 (ORCPT ); Wed, 25 Apr 2018 17:46:56 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E37D1214D5 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=jhogan@kernel.org Date: Wed, 25 Apr 2018 22:46:51 +0100 From: James Hogan To: NeilBrown Cc: Ralf Baechle , Paul Burton , linux-mips@linux-mips.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] MIPS: c-r4k: fix data corruption related to cache coherence. Message-ID: <20180425214650.GA25917@saruman> References: <87sh7klyhc.fsf@notabene.neil.brown.name> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="nFreZHaLTZJo0R7j" Content-Disposition: inline In-Reply-To: <87sh7klyhc.fsf@notabene.neil.brown.name> User-Agent: Mutt/1.7.2 (2016-11-26) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --nFreZHaLTZJo0R7j Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Hi NeilBrown, On Wed, Apr 25, 2018 at 02:08:15PM +1000, NeilBrown wrote: > Cc: stable@vger.kernel.org (v4.8) FYI my preferred form of this is: Cc: # 4.8+ > /* > * Either no secondary cache or the available caches don't have the > * subset property so we have to flush the primary caches > - * explicitly > + * explicitly. > + * As Index type operations are not globalized by CM, we must > + * use the HIT type when CM is present. I don't think Index type operations *can* be sensibly globalised to separate primary caches, since they directly index the lines in the cache rather than any particular physical or virtual address, so this fundamental issue doesn't sound specific to the CM. I'm not entirely clear OTOH whether there are any non-CM r4k-like SMP capable cores that don't have coherent IO or inclusive caches. - Octeon doesn't use c-r4k and has coherent IO - Netlogic appear to have coherent IO=20 - Loongson64 have inclusive caches - bmips, only bmips5000 appears to have multicore (not just multi-thread with I presume shared dcaches), and that has inclusive caches So I suppose that does just leave non-multicore and CM systems as potentially reaching these bits of code... > */ > - if (size >=3D dcache_size) { > + if (!mips_cm_present() && size >=3D dcache_size) { =2E.. but even for CM systems its only if there are foreign CPUs running (i.e. not just threads on the same core sharing the same dcache) that it actually matters. So I'm thinking "!mips_cm_present()" should probably be replaced with "!r4k_op_needs_ipi(R4K_INDEX)" (and the comment updated to mention that IPI calls aren't implemented here). That effectively means: !CONFIG_SMP || cpumask_empty(&cpu_foreign_map[0]) Otherwise the patch looks spot on. Thanks for spotting this! Cheers James --nFreZHaLTZJo0R7j Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- iHUEARYIAB0WIQS7lRNBWUYtqfDOVL41zuSGKxAj8gUCWuD3SgAKCRA1zuSGKxAj 8jxaAQCjN7fGjCbL9rA4R+BAfse5BLH8yfkHr3MGSlqlg1WdgAEAvcze6SBWRFlC LxHvEdBgz+wy9S+LYgU2ERRG62e6FQ0= =j2yT -----END PGP SIGNATURE----- --nFreZHaLTZJo0R7j--