Re: [PATCH v19 086/130] KVM: TDX: restore debug store when TD exit

Chao Gao
2024-04-17T04:03:29Z

On Tue, Apr 16, 2024 at 11:24:16AM -0700, Reinette Chatre wrote:
>Hi Isaku,
>
>On 2/26/2024 12:26 AM, isaku.yamahata@intel.com wrote:
>> From: Isaku Yamahata <isaku.yamahata@intel.com>
>>
>> Because debug store is clobbered, restore it on TD exit.
>>
>
>I am trying to understand why this is needed and finding a few
>places that seem to indicate that this is not needed.
>
>For example, in the TX base spec, section 15.2 "On-TD Performance
>Monitoring", subsection "15.2.1 Overview":
> * IA32_DS_AREA MSR is context-switched across TD entry and exit transitions.
>
>To confirm I peeked at the TDX module code and found (if I understand this
>correctly) that IA32_DS_AREA is saved on TD entry (see [1]) and restored on
>TD exit (see [2]).

Hi Reinette,

You are right. I asked TDX module to preserve IA32_DS_AREA across TD transitions
and they made this change. So, this patch can be dropped now.