linux-kernel - Re: [PATCH v10 6/6] x86/split_lock: Enable split lock detection by kernel parameter

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Message-Id: <B2612A75-BEC8-4FF7-9FDA-A7B55C2E0B4A@amacapital.net>
Date:   Thu, 21 Nov 2019 15:18:46 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v10 6/6] x86/split_lock: Enable split lock detection by kernel parameter



> On Nov 21, 2019, at 2:29 PM, Luck, Tony <tony.luck@...el.com> wrote:
> 
> 
>> 
>> It would be really, really nice if we could pass this feature through to a VM. Can we?
> 
> It's hard because the MSR is core scoped rather than thread scoped.  So on an HT
> enabled system a pair of logical processors gets enabled/disabled together.
> 
> 

Well that sucks.

Could we pass it through if the host has no HT?  Debugging is *so* much easier in a VM.  And HT is a bit dubious these days anyway.