linux-kernel - Re: [PATCH v9 13/17] x86/split_lock: Disable split lock detection by kernel parameter "nosplit_lock

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Date:   Wed, 26 Jun 2019 22:34:52 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Fenghua Yu <fenghua.yu@...el.com>
cc:     Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krcmar <rkrcmar@...hat.com>,
        Christopherson Sean J <sean.j.christopherson@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        x86 <x86@...nel.org>, kvm@...r.kernel.org
Subject: Re: [PATCH v9 13/17] x86/split_lock: Disable split lock detection
 by kernel parameter "nosplit_lock_detect"

On Tue, 18 Jun 2019, Fenghua Yu wrote:
>  
>  static void split_lock_update_msr(void)
>  {
> -	/* Enable split lock detection */
> -	this_cpu_or(msr_test_ctl_cached, MSR_TEST_CTL_SPLIT_LOCK_DETECT);
> +	if (split_lock_detect_enabled) {
> +		/* Enable split lock detection */
> +		this_cpu_or(msr_test_ctl_cached, MSR_TEST_CTL_SPLIT_LOCK_DETECT);
> +	} else {
> +		/* Disable split lock detection */

Could you please comment the non obvious things and not the obvious ones?

> +		this_cpu_and(msr_test_ctl_cached, ~MSR_TEST_CTL_SPLIT_LOCK_DETECT);

It's entirely clear that the if (enabled) path enables it or am I missing
something?

Thanks,

	tglx