linux-kernel - Re: [RFC PATCH v2 60/69] KVM: VMX: Add macro framework to read/write VMCS for VMs and TDs

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Date:   Tue, 13 Jul 2021 20:56:12 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     isaku.yamahata@...el.com, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, erdemaktas@...gle.com,
        Connor Kuehl <ckuehl@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        isaku.yamahata@...il.com,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [RFC PATCH v2 60/69] KVM: VMX: Add macro framework to read/write
 VMCS for VMs and TDs

On Tue, Jul 06, 2021, Paolo Bonzini wrote:
> On 03/07/21 00:05, isaku.yamahata@...el.com wrote:
> > From: Sean Christopherson <sean.j.christopherson@...el.com>
> > 
> > Add a macro framework to hide VMX vs. TDX details of VMREAD and VMWRITE
> > so the VMX and TDX can shared common flows, e.g. accessing DTs.
> > 
> > Note, the TDX paths are dead code at this time.  There is no great way
> > to deal with the chicken-and-egg scenario of having things in place for
> > TDX without first having TDX.
> > 
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> > ---
> >   arch/x86/kvm/vmx/common.h | 41 +++++++++++++++++++++++++++++++++++++++
> >   1 file changed, 41 insertions(+)
> > 
> > diff --git a/arch/x86/kvm/vmx/common.h b/arch/x86/kvm/vmx/common.h
> > index 9e5865b05d47..aa6a569b87d1 100644
> > --- a/arch/x86/kvm/vmx/common.h
> > +++ b/arch/x86/kvm/vmx/common.h
> > @@ -11,6 +11,47 @@
> >   #include "vmcs.h"
> >   #include "vmx.h"
> >   #include "x86.h"
> > +#include "tdx.h"
> > +
> > +#ifdef CONFIG_KVM_INTEL_TDX
> 
> Is this #ifdef needed at all if tdx.h properly stubs is_td_vcpu (to return
> false) and possibly declares a dummy version of td_vmcs_read/td_vmcs_write?

IIRC, it requires dummy versions of is_debug_td() and all the ##bits variants of
td_vmcs_read/write().  I'm not sure if I ever actually tried that, e.g. to see
if the compiler completely elided the TDX crud when CONFIG_KVM_INTEL_TDX=n.