linux-kernel - Re: [PATCH] x86/bugs/multihit: Fix mitigation reporting when KVM is not in use

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Date:   Tue, 14 Jul 2020 14:20:59 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...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>,
        "Gomez Iglesias, Antonio" <antonio.gomez.iglesias@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Anthony Steinhauser <asteinhauser@...gle.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Mark Gross <mgross@...ux.intel.com>,
        Waiman Long <longman@...hat.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH] x86/bugs/multihit: Fix mitigation reporting when KVM is
 not in use

On 7/14/20 2:04 PM, Pawan Gupta wrote:
>> I see three inputs and four possible states (sorry for the ugly table,
>> it was this or a spreadsheet :):
>>
>> X86_FEATURE_VMX	CONFIG_KVM_*	hpage split  Result	   Reason
>> 	N			x	    x	     Not Affected  No VMX
>> 	Y			N	    x	     Not affected  No KVM
>> 	Y			Y	    Y	     Mitigated	   hpage split
>> 	Y			Y	    N	     Vulnerable
> Thank you.
> 
> Just a note... for the last 2 cases kernel wont know about "hpage split"
> mitigation until KVM is loaded. So for these cases reporting at boot
> will be "Vulnerable" and would change to "Mitigated" once KVM is loaded
> and deploys the mitigation. This is the current behavior.

That's OK with me, because it's actually pretty closely tied to reality.
 You are literally "vulnerable" until you've committed to a mitigation
and that doesn't happen until KVM is loaded.

When are we going to force kvm to be built in, again? ;)