linux-kernel - Re: [PATCH v4 10/19] x86/cpu: Detect VMX features on Intel, Centaur and Zhaoxin CPUs

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Date:   Thu, 12 Dec 2019 19:24:55 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Tony Luck <tony.luck@...el.com>,
        Tony W Wang-oc <TonyWWang-oc@...oxin.com>,
        Len Brown <lenb@...nel.org>, Shuah Khan <shuah@...nel.org>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-edac@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Subject: Re: [PATCH v4 10/19] x86/cpu: Detect VMX features on Intel, Centaur
 and Zhaoxin CPUs

On Thu, Dec 12, 2019 at 09:55:11AM -0800, Sean Christopherson wrote:
> The reasoning behind using vanilla rdmsr() on PROC and PIN controls is that
> those MSRs should exist on any CPU that supports VMX, i.e. we want the WARN.
> 
> The alternative would be to use rdmsr_safe() for everything and then
> explicitly disable VMX if a fault on PROC or PIN occurs, but that circles
> us back to the handling a fault on rdmsr(MSR_IA32_FEAT_CTL), i.e. is it
> really worth gracefully handling a fault that should never occur?

No but pls put a comment above it explaining why we're doing rdmsr()
only with those two MSRs.

Thx.

-- 
Regards/Gruss,
    Boris.

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