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 12:17:59 -0700
From:   Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.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 Tue, Jul 14, 2020 at 07:57:53AM -0700, Dave Hansen wrote:
> Let's stick to things which are at least static per reboot.  Checking
> for X86_FEATURE_VMX or even CONFIG_KVM_INTEL seems like a good stopping
> point.  "Could this kernel run a naughty guest?"  If so, report
> "Vulnerable".  It's the same as Meltdown: "Could this kernel run
> untrusted code?"  If so, report "Vulnerable".

Thanks, These are good inputs. So what I need to add is a boot time
check for VMX feature and report "Vulnerable" or "Not
affected(VMX disabled)".

Are you suggesting to not change the reporting when KVM deploys the
"Split huge pages" mitigation? Is this because VMX can still be used by
other VMMs?

The current mitigation reporting is very specific to KVM:

	- "KVM: Vulnerable"
	- "KVM: Mitigation: Split huge pages"

As the kernel doesn't know about the mitigation state of out-of-tree
VMMs can we add VMX reporting to always say vulnerable when VMX is
enabled:

	- "VMX: Vulnerable, KVM: Vulnerable"
	- "VMX: Vulnerable, KVM: Mitigation: Split huge pages"

And if VMX is disabled report:

	- "VMX: Not affected(VMX disabled)"

or something like that.

Thanks,
Pawan