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Date:   Sat, 25 Jan 2020 23:17:38 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     "Luck, Tony" <tony.luck@intel.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Arvind Sankar <nivedita@alum.mit.edu>,
        "Christopherson, Sean J" <sean.j.christopherson@intel.com>,
        Ingo Molnar <mingo@kernel.org>,
        "Yu, Fenghua" <fenghua.yu@intel.com>,
        Ingo Molnar <mingo@redhat.com>, H Peter Anvin <hpa@zytor.com>,
        "Raj, Ashok" <ashok.raj@intel.com>,
        "Shankar, Ravi V" <ravi.v.shankar@intel.com>,
        linux-kernel <linux-kernel@vger.kernel.org>, x86 <x86@kernel.org>
Subject: Re: [PATCH v15] x86/split_lock: Enable split lock detection by kernel
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On Sat, Jan 25, 2020 at 01:42:32PM -0800, Luck, Tony wrote:
> On Sat, Jan 25, 2020 at 09:33:12PM +0100, Borislav Petkov wrote:
> > On Sat, Jan 25, 2020 at 09:12:21PM +0100, Peter Zijlstra wrote:
> > > My thinking was Virt, virt likes to mess up all msr expectations.
> > 
> > My only worry is to have it written down why we're doing this so that it
> > can be changed/removed later, when we've forgotten all about split lock.
> > Because pretty often we look at a comment-less chunk of code and wonder,
> > "why the hell did we add this in the first place."
> 
> Ok. I added a comment:
> 
>  * Use the "safe" versions of rdmsr/wrmsr here because although code
>  * checks CPUID and MSR bits to make sure the TEST_CTRL MSR should
>  * exist, there may be glitches in virtualization that leave a guest
>  * with an incorrect view of real h/w capabilities.

Yap, nice.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette