Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <7f27a51961d212c17933b39ea0b5b884c2939ff9.camel@intel.com>
Subject: Re: [PATCH v7 101/102] Documentation/virtual/kvm: Document on Trust
 Domain Extensions(TDX)
From:   Kai Huang <kai.huang@intel.com>
To:     isaku.yamahata@intel.com, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     isaku.yamahata@gmail.com, Paolo Bonzini <pbonzini@redhat.com>
Date:   Fri, 08 Jul 2022 13:34:20 +1200
In-Reply-To: <9e54fa1ac03df3cd2fb7a2e64d3cffc35d4f097e.1656366338.git.isaku.yamahata@intel.com>
References: <cover.1656366337.git.isaku.yamahata@intel.com>
         <9e54fa1ac03df3cd2fb7a2e64d3cffc35d4f097e.1656366338.git.isaku.yamahata@intel.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
User-Agent: Evolution 3.44.2 (3.44.2-1.fc36) 
MIME-Version: 1.0
Precedence: bulk


> +
> +- Wrapping kvm x86_ops: The current choice
> +  Introduce dedicated file for arch/x86/kvm/vmx/main.c (the name,
> +  main.c, is just chosen to show main entry points for callbacks.) and
> +  wrapper functions around all the callbacks with
> +  "if (is-tdx) tdx-callback() else vmx-callback()".
> +
> +  Pros:
> +  - No major change in common x86 KVM code. The change is (mostly)
> +    contained under arch/x86/kvm/vmx/.
> +  - When TDX is disabled(CONFIG_INTEL_TDX_HOST=3Dn), the overhead is
> +    optimized out.
> +  - Micro optimization by avoiding function pointer.
> +  Cons:
> +  - Many boiler plates in arch/x86/kvm/vmx/main.c.
> +
> +Alternative:
> +- Introduce another callback layer under arch/x86/kvm/vmx.
> +  Pros:
> +  - No major change in common x86 KVM code. The change is (mostly)
> +    contained under arch/x86/kvm/vmx/.
> +  - clear separation on callbacks.
> +  Cons:
> +  - overhead in VMX even when TDX is disabled(CONFIG_INTEL_TDX_HOST=3Dn)=
.
> +

Why putting "Alternative" in the documentation?  You may put it to the cove=
r
letter so people can judge whether the design is reasonable, but it should =
not
be in the documentation.

--=20
Thanks,
-Kai