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

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Message-ID: <87tv2fovag.fsf@nanos.tec.linutronix.de>
Date:   Mon, 23 Mar 2020 18:06:31 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Luck\, Tony" <tony.luck@...el.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     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

"Luck, Tony" <tony.luck@...el.com> writes:

> 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?

Only if they are broken ....