Re: [PATCH v6 00/29] Add AMD Secure Nested Paging (SEV-SNP) support

["Brijesh Singh" <brijesh.singh@amd.com>]

Hi Min,

On 9/8/21 7:31 PM, Xu, Min M wrote:
> On September 9, 2021 3:46 AM, Brijesh Singh wrote:
>> Thank you so much Yao for reviewing the patches. Based on some comments
>> from Gerd I may update code around the reset vector area (mainly use the
>> metadata format etc). For your comments regarding the introducing a new
>> PcdConfidentialComputingCategory I will look to see what I can come up with
>> and in UefiCpuPkg I will try to move all the SEV specific functions in new files
>> (where applicable).
>>
> Hi, Brijesh
> if you are considering to introduce a new PcdConfidentialComputingCategory
> as Jiewen suggested below:
>>> 0008-UefiCpuPkg-Define-the-SEV-SNP-specific-dynamic-PCDs
>>> I really don't like the idea to use BOOL PcdSevEsIsEnabled and
>> PcdSevSnpIsEnabled.
>>> Can we define *one* PCD - such as PcdConfidentialComputingCategory?
>>> We can assign range 0x0000~0xFFFF to AMD SEV, 0x10000~0x1FFFF to Intel
>> TDX.
>>> Then SEV=0x0000, SEV-ES=0x0001, SEV-SNP=0x0002, and TDX=0x10000
>> later.
>>> I really don't want to keep adding PCD endlessly in the future, like
>> PcdSevXXXIsEnabled, PcdSevYYYIsEnabled, PcdTdxIsEnabled,
>> PcdTdx20Enabled, PcdTdx30Enabled, ......
> I also have some suggestions.
>
> As we have below definition in WorkArea.h
>   typedef struct _CONFIDENTIAL_COMPUTING_WORK_AREA_HEADER {
>     UINT8                   GuestType;
>     UINT8                   Reserved1[3];
>   } CONFIDENTIAL_COMPUTING_WORK_AREA_HEADER;
>
> Can we update above CONFIDENTIAL_COMPUTING_WORK_AREA_HEADER to below:
>   typedef struct _CONFIDENTIAL_COMPUTING_WORK_AREA_HEADER {
>     UINT8                   GuestType;
>     UINT8                   SubType;               // subtype which indicates SEV-ES, SEV-NP, or TDX 1.0, TDX 2.0 etc.
>     UINT8                   Reserved1[2];
>   } CONFIDENTIAL_COMPUTING_WORK_AREA_HEADER;
>
> The PcdConfidentialComputingCategory can be defined as UINT32, like below:
>   ## This dynamic PCD indicates the Confidential Computing Category
>   #  [7:0]   Confidential Computing Category  (0 - Non-Cc, 1 - AmdSev, 2 - IntelTdx)
>   #  [15:8]  Sub-Category (defined by each vendor, SEV-ES, SEV-SNP, or TDX-1.0, TDX-2.0, etc)
>   #  [31:16] Reserved
>   # @Prompt Confidential Computing Category
>   gUefiCpuPkgTokenSpaceGuid.PcdConfidentialComputingCategory|0|UINT32|0x60000018
>
> So that we simply copy the CONFIDENTIAL_COMPUTING_WORK_AREA_HEADER to PcdConfidentialComputingCategory.
> What's your thought?

I am not sure if its a good idea to pack a header like above in a 32-bit
PCD. The caller need to unpack the 32-bit number and perform a bitshit
etc. Additionally we also need to check for reserved bits being set to
zero etc. I am more inclined toward something like this:

enum {

   /* The guest is running with memory encryption disabled. */

    CC_ATTR_UNDEF,

  /* The guest is running with active AMD SEV memory encryption. */

   CC_ATTR_AMD_SEV,

  /* The guest is running with active AMD SEV-ES memory encryption. */

  CC_ATTR_AMD_SEV_ES,

  /* The guest is running with active AMD SEV-SNP memory encryption. */

  CC_ATTR_AMD_SEV_SNP,

 /* The guest is running with active Intel TDX memory encryption. */

 CC_ATTR_INTEL_TDX,

 /* The guest is running with active Intel SGX memory encryption. */

 CC_ATTR_INTEL_SGX,

} ConfidentialComputingAttr;

The PcdConfidentialComputingAttr will be set to zero. The OVMF will set
this dynamic PCD in PEI phase. The UefiCpuPkg will provide a new
function that can be used by anyone to check the CC guest type.

BOOLEAN

CcPlatformHas(enum ConfidentialComputingAttr attr)

{

    UINT32 Val;

    Val = PcdGet32 (PcdConfidentialComputingAttr);

    return val == attr;

}


> Thanks!
> Min