Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932652AbcCKPfJ (ORCPT ); Fri, 11 Mar 2016 10:35:09 -0500 Received: from g4t3427.houston.hp.com ([15.201.208.55]:42844 "EHLO g4t3427.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932105AbcCKPfH (ORCPT ); Fri, 11 Mar 2016 10:35:07 -0500 Message-ID: <1457713660.6393.55.camel@hpe.com> Subject: Re: [PATCH 1/2] x86/mm/pat: Change pat_disable() to emulate PAT table From: Toshi Kani To: Borislav Petkov Cc: "mingo@kernel.org" , "bp@suse.de" , "hpa@zytor.com" , "tglx@linutronix.de" , "mcgrof@suse.com" , "jgross@suse.com" , "paul.gortmaker@windriver.com" , "x86@kernel.org" , "linux-kernel@vger.kernel.org" Date: Fri, 11 Mar 2016 09:27:40 -0700 In-Reply-To: <20160311091229.GA4347@pd.tnic> References: <1457671546-13486-1-git-send-email-toshi.kani@hpe.com> <1457671546-13486-2-git-send-email-toshi.kani@hpe.com> <20160311091229.GA4347@pd.tnic> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.18.4 (3.18.4-1.fc23) Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2210 Lines: 64 On Fri, 2016-03-11 at 09:12 +0000, Borislav Petkov wrote: > On Thu, Mar 10, 2016 at 09:45:45PM -0700, Toshi Kani wrote:  : > >   > > -static inline void pat_disable(const char *reason) > > +void pat_disable(const char *reason) > >  { > > + if (boot_cpu_done) { > > + pr_info("x86/PAT: PAT cannot be disabled after > > initialized\n"); > > pr_err() Will do. > > > + return; > > + } > > + > >   __pat_enabled = 0; > >   pr_info("x86/PAT: %s\n", reason); > > + > > + pat_disable_init(); > > Why can't you call pat_init() here simply? It checks pat_enabled(). You > can call it pat_setup() or so if it looks confusing to call an init > function in a disable function... How about pat_disable_setup()?  It's only used for the disabled case, so I'd prefer to keep the word "disable". Yes, calling pat_init() from pat_disable() works too. I changed it in this way because:  - pat_bsp_init() calls pat_disabled() in an error case. It is simpler to avoid a recursive call to pat_init().  - pat_bsp_init() has two different error paths, 1) call pat_disable() and return, and 2) goto done and call pat_init_cache_modes(). We can remove case 2) to keep the error handling consistent in this way. > Then you don't have to add yet another static disable_init_done but rely > on boot_cpu_done which gets set in pat_init(). Right, but it will do 'boot_cpu_done = true' twice, and this implicit recursive call may cause an issue in future if someone makes change carelessly. > Also, I don't see the static_cpu_has() check I suggested yesterday - we > need to check the feature bits if PAT gets disabled early on some old > Intels. Sorry, I should have mentioned it. I ended up not needing this change. The table in patch 2/2 covers this case as:   MTRR   PAT    ACTION   ====================================================================   E      D      MTRR calls pat_init() -> PAT disabled per cpu_has_pat That is, the check with cpu_has_pat in pat_bsp_init() calls pat_disable() in this case. I preferred this way because it will continue to log a message "PAT not supported by CPU.", and keeps __pat_enabled as the single variable to manage the PAT state. Thanks, -Toshi