linux-kernel - Re: [PATCH v5 2/9] x86/split_lock: Avoid runtime reads of the TEST

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Message-ID: <20200321004315.GB6578@agluck-desk2.amr.corp.intel.com>
Date:   Fri, 20 Mar 2020 17:43:15 -0700
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        hpa@...or.com, Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        kvm@...r.kernel.org, x86@...nel.org, linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH v5 2/9] x86/split_lock: Avoid runtime reads of the
 TEST_CTRL MSR

On Sun, Mar 15, 2020 at 01:05:10PM +0800, Xiaoyao Li wrote:
> In a context switch from a task that is detecting split locks
> to one that is not (or vice versa) we need to update the TEST_CTRL
> MSR. Currently this is done with the common sequence:
> 	read the MSR
> 	flip the bit
> 	write the MSR
> in order to avoid changing the value of any reserved bits in the MSR.
> 
> Cache the value of the TEST_CTRL MSR when we read it during initialization
> so we can avoid an expensive RDMSR instruction during context switch.
> 
> Suggested-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Originally-by: Tony Luck <tony.luck@...el.com>
> Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>

Is it bad form to Ack/Review patches originally by oneself?

Whatever:

Acked-by: Tony Luck <tony.luck@...el.com>