Re: [PATCH Part1 RFC v3 20/22] x86/boot: Add Confidential Computing address to setup_header

[Brijesh Singh]

On 6/18/2021 1:08 AM, Borislav Petkov wrote:
> On Wed, Jun 02, 2021 at 09:04:14AM -0500, Brijesh Singh wrote:
>> While launching the encrypted guests, the hypervisor may need to provide
>> some additional information that will used during the guest boot. In the
>> case of AMD SEV-SNP the information includes the address of the secrets
>> and CPUID pages. The secrets page contains information such as a VM to
>> PSP communication key and CPUID page contain PSP filtered CPUID values.
>>
>> When booting under the EFI based BIOS, the EFI configuration table
>> contains an entry for the confidential computing blob. In order to support
>> booting encrypted guests on non EFI VM, the hypervisor to pass these
>> additional information to the kernel with different method.
>>
>> For this purpose expand the struct setup_header to hold the physical
>> address of the confidential computing blob location. Being zero means it
>> isn't passed.
>>
>> Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
>> ---
>>  Documentation/x86/boot.rst            | 27 +++++++++++++++++++++++++++
>>  arch/x86/boot/header.S                |  7 ++++++-
>>  arch/x86/include/uapi/asm/bootparam.h |  1 +
>>  3 files changed, 34 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/x86/boot.rst b/Documentation/x86/boot.rst
>> index fc844913dece..9b32805617bb 100644
>> --- a/Documentation/x86/boot.rst
>> +++ b/Documentation/x86/boot.rst
>> @@ -75,6 +75,8 @@ Protocol 2.14	BURNT BY INCORRECT COMMIT
>>  		DO NOT USE!!! ASSUME SAME AS 2.13.
>>  
>>  Protocol 2.15	(Kernel 5.5) Added the kernel_info and kernel_info.setup_type_max.
>> +
>> +Protocol 2.16	(Kernel 5.14) Added the confidential computing blob address
>>  =============	============================================================
>>  
>>  .. note::
>> @@ -226,6 +228,7 @@ Offset/Size	Proto		Name			Meaning
>>  0260/4		2.10+		init_size		Linear memory required during initialization
>>  0264/4		2.11+		handover_offset		Offset of handover entry point
>>  0268/4		2.15+		kernel_info_offset	Offset of the kernel_info
>> +026C/4		2.16+		cc_blob_address	        Physical address of the confidential computing blob
> 
> Why is this a separate thing instead of being passed as setup_data?
> 

Don't have any strong reason to keep it separate, I can define a new type and use the
setup_data to pass this information.

-Brijesh