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Date: Thu, 28 Mar 2024 14:03:42 -0700
From: Isaku Yamahata <isaku.yamahata@intel.com>
To: Binbin Wu <binbin.wu@linux.intel.com>
Cc: isaku.yamahata@intel.com, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org, isaku.yamahata@gmail.com,
	Paolo Bonzini <pbonzini@redhat.com>, erdemaktas@google.com,
	Sean Christopherson <seanjc@google.com>,
	Sagi Shahar <sagis@google.com>, Kai Huang <kai.huang@intel.com>,
	chen.bo@intel.com, hang.yuan@intel.com, tina.zhang@intel.com,
	isaku.yamahata@linux.intel.com
Subject: Re: [PATCH v19 069/130] KVM: TDX: Require TDP MMU and mmio caching
 for TDX
Message-ID: <20240328210342.GR2444378@ls.amr.corp.intel.com>
References: <cover.1708933498.git.isaku.yamahata@intel.com>
 <f6a80dd212e8c3fd14b40049eed33187008cf35a.1708933498.git.isaku.yamahata@intel.com>
 <94fb2094-d8ee-4bcc-a65d-489dc777b024@linux.intel.com>
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On Thu, Mar 28, 2024 at 01:24:27PM +0800,
Binbin Wu <binbin.wu@linux.intel.com> wrote:

> 
> 
> On 2/26/2024 4:26 PM, isaku.yamahata@intel.com wrote:
> > From: Isaku Yamahata <isaku.yamahata@intel.com>
> > 
> > As TDP MMU is becoming main stream than the legacy MMU, the legacy MMU
> > support for TDX isn't implemented.  TDX requires KVM mmio caching.
> 
> Can you add some description about why TDX requires mmio caching in the
> changelog?

Sure, will update the commit log.

As the TDX guest is protected, the guest has to issue TDG.VP.VMCALL<MMIO> on
VE.  The VMM has to setup Shared-EPT entry to inject VE by setting the entry
value with VE suppress bit cleared.

KVM mmio caching is a feature to set the EPT entry to special value for MMIO GFN
instead of the default value with suppress VE bit set.  So TDX KVM wants to
utilize it.

Thanks,
-- 
Isaku Yamahata <isaku.yamahata@intel.com>