linux-kernel - Re: [PATCH v5 1/3] x86/cpufeatures: Enumerate #DB for bus lock detection

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Message-ID: <877dm26fvo.fsf@nanos.tec.linutronix.de>
Date:   Fri, 19 Mar 2021 21:35:39 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Fenghua Yu <fenghua.yu@...el.com>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Tony Luck <tony.luck@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>,
        Fenghua Yu <fenghua.yu@...el.com>
Subject: Re: [PATCH v5 1/3] x86/cpufeatures: Enumerate #DB for bus lock detection

On Sat, Mar 13 2021 at 05:49, Fenghua Yu wrote:
> A bus lock is acquired though either split locked access to

s/though/through/
either a 

> writeback (WB) memory or any locked access to non-WB memory. This is
> typically >1000 cycles slower than an atomic operation within a cache
> line. It also disrupts performance on other cores.
>
> Some CPUs have ability to notify the kernel by an #DB trap after a user

the ability

> instruction acquires a bus lock and is executed. This allows the kernel
> to enforce user application throttling or mitigations. Both breakpoint
> and bus lock can trigger the #DB trap in the same instruction and the
> ordering of handling them is the kernel #DB handler's choice.

Thanks,

        tglx