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

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Message-ID: <20200715180413.GB12349@linux.intel.com>
Date:   Wed, 15 Jul 2020 11:04:13 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc:     Dave Hansen <dave.hansen@...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 Wed, Jul 15, 2020 at 10:18:20AM -0700, Pawan Gupta wrote:
> On Tue, Jul 14, 2020 at 05:51:30PM -0700, Sean Christopherson wrote:
> > On Tue, Jul 14, 2020 at 02:20:59PM -0700, Dave Hansen wrote:
> > > 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
> > 
> > This line item is pointless, the relevant itlb_multihit_show_state()
> > implementation depends on CONFIG_KVM_INTEL.  The !KVM_INTEL version simply
> > prints ""Processor vulnerable".
> 
> While we are on it, for CONFIG_KVM_INTEL=n would it make sense to report "Not
> affected(No KVM)"? "Processor vulnerable" is not telling much about the
> mitigation.

I know we don't care too much about out-of-tree hypervisors, but IMO stating
"Not affected" is unnecessarily hostile and "Processor vulnerable" is an
accurate statement.