[edk2-devel] [PATCH V3 06/10] OvmfPkg: Add AmdSev.asm in ResetVector

[Yao, Jiewen]

It does not necessary to be a working area.

We just need a common TEE flag to indicate if the system run in legacy, SEV, or TDX, right?

thank you!
Yao, Jiewen


> 在 2021年7月28日，下午1:07，Xu, Min M <min.m.xu at intel.com> 写道：
> 
> On July 27, 2021 8:46 PM, Yao, Jiewen wrote:
>> HI Min
>> I agree with Brijesh.
>> 
>> The basic rule is: SEV file shall never refer to TDX data structure. TDX file
>> shall never refer to SEV data structure.
>> These code should be isolated clearly.
>> 
>> Do we still need that logic if we follow the new pattern?
> I have replied to Brijesh's mail about the concern of the new pattern. 
> 
> I have some concern in the current pattern:
> ====================
>    OneTimeCall   PreMainFunctionHookSev
>    OneTimeCall   PreMainFunctionHookTdx
> MainFunction:
>    XXXXXX
>    OneTimeCall   PostMainFunctionHookSev
>    OneTimeCall   PostMainFunctionHookTdx
> ====================
> The TEE function need implement a TEE check function (such as IsSev, or IsTdx). 
> 
> Tdx call CPUID(0x21) to determine if it is tdx guest in the very beginning of ResetVector. Then 'TDXG' is set
> in TDX_WORK_AREA. SEV does the similar work which call CheckSevFeatures to set SEV_ES_WORK_AREA to 1.
> 
> After that both TDX and SEV read the above WORK_AREA to check if it is TDX or SEV or legacy guest.
> 
> In Tdx the access to SEV_ES_WORK_AREA will trigger error because SEV_ES_WORK_AREA is *NOT* initialized by host VMM.
> In SEV-SNP I am afraid the access to TDX_WORK_AREA will trigger error too.
> 
> I am wondering if TDX and SEV can use the same memory region (for example, TEE_WORK_AREA) as the work area?
> So that this work area is guaranteed to be initialized in both TDX and SEV. Structure of the TEE_WORK_AREA may
> look like this:
>  typedef struct {
>      UINT8  Flag[4];         'TDXG' or 'SEVG' or all-0
>      UINT8  Others[];
>  } TEE_WORK_AREA;
>> 


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