linux-kernel - Re: [PATCH v2 05/16] KVM: VMX: Drop initialization of IA32_FEATURE

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Date:   Tue, 22 Oct 2019 12:51:01 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org
Cc:     "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        Radim Krčmář <rkrcmar@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>, kvm@...r.kernel.org
Subject: Re: [PATCH v2 05/16] KVM: VMX: Drop initialization of
 IA32_FEATURE_CONTROL MSR

On 22/10/19 02:08, Sean Christopherson wrote:
> Remove the code to initialize IA32_FEATURE_CONTROL MSR when KVM is
> loaded now that the MSR is initialized during boot on all CPUs that
> support VMX, i.e. can possibly load kvm_intel.
> 
> Reviewed-by: Jim Mattson <jmattson@...gle.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 48 +++++++++++++++++-------------------------
>  1 file changed, 19 insertions(+), 29 deletions(-)

I am still not sure about this...  Enabling VMX is adding a possible
attack vector for the kernel, we should not do it unless we plan to do a
VMXON.  Why is it so important to operate with locked
IA32_FEATURE_CONTROL (so that KVM can enable VMX and the kernel can
still enable SGX if desired).

Paolo