Re: [PATCH V4 2/2] OvmfPkg: Update CcProbeLib to DxeCcProbeLib

["Lendacky, Thomas" <thomas.lendacky@amd.com>]

On 8/26/22 18:07, Min Xu wrote:
> From: Min M Xu <min.m.xu@intel.com>
> 
> 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 redesigned 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 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.
> 
> To gurantee the GuestType is cached, we read the value in both

s/gurantee/guarantee/

> constructor and CcProbe. Because in some corner case, the constructor
> may be called after CcProbe. For example in MdeModulePkg/Core/Dxe/DxeMain,
> BaseDebugLibSerialPortConstructor is called before
> DxeCcProbeLibConstructor. While CcProbe () is called in
> BaseDebugLibSerialPortConstructor.

Is there a way to put some kind of ordering in place so that CcProbe's 
constructor is called before BaseDebugLibSerialPortConstructor?

> 
> 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

s/varialbe/variable/

Thanks,
Tom

> very frequently.
> 
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Cc: Erdem Aktas <erdemaktas@google.com>
> Cc: James Bottomley <jejb@linux.ibm.com>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Signed-off-by: Min Xu <min.m.xu@intel.com>
> ---