linux-kernel - Re: [PATCH v10 005/108] KVM: TDX: Initialize the TDX module when loading the KVM intel kernel module

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Date:   Tue, 8 Nov 2022 18:48:46 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     "Huang, Kai" <kai.huang@...el.com>
Cc:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "Aktas, Erdem" <erdemaktas@...gle.com>,
        "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
        "dmatlack@...gle.com" <dmatlack@...gle.com>
Subject: Re: [PATCH v10 005/108] KVM: TDX: Initialize the TDX module when
 loading the KVM intel kernel module

On Tue, Nov 08, 2022, Huang, Kai wrote:
> > +int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops)
> > +{
> > +	int r;
> > +
> > +	if (!enable_ept) {
> > +		pr_warn("Cannot enable TDX with EPT disabled\n");
> > +		return -EINVAL;
> > +	}
> > +
> > +	/* MOVDIR64B instruction is needed. */
> > +	if (!static_cpu_has(X86_FEATURE_MOVDIR64B)) {

Nit unrelated to Kai's comments: use boot_cpu_has(), not static_cpu_has().  This
is run-once code that's not a hot path so there's zero reason to trigger patching.

> > +		pr_warn("Cannot enable TDX with MOVDIR64B supported ");
> 					   ^
> 					   without
> > +		return -ENODEV;
> > +	}
> 
> I think you should explain why MOVDIR64B is required, otherwise this just comes
> out of blue.
> 
> Btw, is this absolutely required?  TDX also supports Li-mode, which doesn't have
> integrity check.  So theoretically with Li-mode, normal zeroing is also OK but
> doesn't need to use MOVDIR64B.
> 
> That being said, do we have a way to tell whether TDX works in Ci or Li mode?
> 
> 
>