linux-kernel - Re: [PATCH v8 13/15] x86/split_lock: Enable split lock detection by default

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Date:   Thu, 25 Apr 2019 13:41:37 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     'Thomas Gleixner' <tglx@...utronix.de>,
        'Fenghua Yu' <fenghua.yu@...el.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Christopherson Sean J <sean.j.christopherson@...el.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        Michael Chan <michael.chan@...adcom.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        x86 <x86@...nel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>
Subject: Re: [PATCH v8 13/15] x86/split_lock: Enable split lock detection by
 default

On Thu, Apr 25, 2019 at 11:13:23AM +0000, David Laight wrote:
> I'm not at all sure that 'compare and exchange' operations
> are atomic on all cpus if the data is misaligned and crosses
> a page boundary and either (or both) pages need faulting in
> (or hit a TLB miss).

Most sane architectures already trap if you attempt that.