Re: [PATCH V4 0/2] Re-design CcProbeLib

["Gerd Hoffmann" <kraxel@redhat.com>]

On Sat, Aug 27, 2022 at 07:07:06AM +0800, Min Xu wrote:
> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3974
> 
> CcProbeLib once was designed to probe the Confidential Computing guest
> type by checking the PcdOvmfWorkArea. But this memory is allocated with
> either EfiACPIMemoryNVS or EfiBootServicesData. It cannot be accessed
> after ExitBootService. Please see the detailed analysis in BZ#3974.
> 
> To fix this issue, CcProbeLib is re-designed as 2 implementation:
>  - SecPeiCcProbeLib
>  - DxeCcProbeLib
> 
> In SecPeiCcProbeLib we check the CC guest type by reading the
> PcdOvmfWorkArea. Because it is used in SEC / PEI and we don't worry about
> the issues in BZ#3974.
> 
> In DxeCcProbeLib we cache the GuestType in Ovmf work area in a global
> variable. After that the Guest type is returned with the cached value.
> So that we don't need to worry about the access to Ovmf work area after
> ExitBootService.
> 
> The reason why we probe CC guest type in 2 different ways is the global
> varialbe. Global variable cannot be used in SEC/PEI and CcProbe is called
> very frequently.
> 
> Code: https://github.com/mxu9/edk2/tree/CcProbeLib.BZ3974.v4
> 
> v4 changes:
>  - Read Cc guest type in both DxeCcProbeLib's constructor and CcProbe. So
>    that we guarantee the Cc guest type is read early enough.

Acked-by: Gerd Hoffmann <kraxel@redhat.com>

take care,
  Gerd