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[84.3.50.134]) by smtp.gmail.com with ESMTPSA id v184sm297255wme.31.2019.11.21.09.14.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 21 Nov 2019 09:14:03 -0800 (PST) Date: Thu, 21 Nov 2019 18:14:01 +0100 From: Ingo Molnar To: Fenghua Yu Cc: Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , H Peter Anvin , Tony Luck , Ashok Raj , Ravi V Shankar , linux-kernel , x86 Subject: Re: [PATCH v10 6/6] x86/split_lock: Enable split lock detection by kernel parameter Message-ID: <20191121171401.GE12042@gmail.com> References: <1574297603-198156-1-git-send-email-fenghua.yu@intel.com> <1574297603-198156-7-git-send-email-fenghua.yu@intel.com> <20191121060444.GA55272@gmail.com> <20191121130153.GS4097@hirez.programming.kicks-ass.net> <20191121161410.GA199273@romley-ivt3.sc.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191121161410.GA199273@romley-ivt3.sc.intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Fenghua Yu wrote: > > This feature MUST be default enabled, otherwise everything will > > be/remain broken and we'll end up in the situation where you can't > > use it even if you wanted to. > > The usage scope of this patch set is largely reduced to only real time. > The long split lock processing time (>1000 cycles) cannot be tolerated > by real time. > > Real time customers do want to use this feature to detect the fatal > split lock error. They don't want any split lock issue from BIOS/EFI/ > firmware/kerne/drivers/user apps. > > Real time can enable the feature (set bit 29 in TEST_CTRL MSR) in BIOS > and don't need OS to enable it. But, #AC handler cannot handle split > lock in the kernel and will return to the faulting instruction and > re-enter #AC. So current #AC handler doesn't provide useful information > for the customers. That's why we add the new #AC handler in this patch > set. Immaterial - for this feature to be useful it must be default-enabled, with reasonable quirk knobs offered to people who happen to be bitten by such bugs and cannot fix the software. But default-enabled is a must-have, as Peter said. Thanks, Ingo