linux-kernel - Re: [PATCH v4 1/4] KVM: TDX: Synchronize user-return MSRs immediately after VP.ENTER

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Message-ID: <d1628f0e-bbe9-48b0-8881-ad451d4ce9c5@intel.com>
Date: Tue, 21 Oct 2025 16:37:48 +0300
From: Adrian Hunter <adrian.hunter@...el.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "kas@...nel.org" <kas@...nel.org>, "seanjc@...gle.com"
	<seanjc@...gle.com>
CC: "Li, Xiaoyao" <xiaoyao.li@...el.com>, "kvm@...r.kernel.org"
	<kvm@...r.kernel.org>, "linux-coco@...ts.linux.dev"
	<linux-coco@...ts.linux.dev>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Zhao, Yan Y" <yan.y.zhao@...el.com>,
	"x86@...nel.org" <x86@...nel.org>, "hou, wenlong"
	<houwenlong.hwl@...group.com>
Subject: Re: [PATCH v4 1/4] KVM: TDX: Synchronize user-return MSRs immediately
 after VP.ENTER

On 21/10/2025 01:55, Edgecombe, Rick P wrote:
>> +	 * Several of KVM's user-return MSRs are clobbered by the TDX-Module if
>> +	 * VP.ENTER succeeds, i.e. on TD-Exit.  Mark those MSRs as needing an
>> +	 * update to synchronize the "current" value in KVM's cache with the
>> +	 * value in hardware (loaded by the TDX-Module).
>> +	 */
> 
> I think we should be synchronizing only after a successful VP.ENTER with a real
> TD exit, but today instead we synchronize after any attempt to VP.ENTER.

If the MSR's do not get clobbered, does it matter whether or not they get
restored.