Re: [PATCH 1/4] x86/hyperv: Add missing ARCH_HAS_CC_PLATFORM dependency

[Tianyu Lan <ltykernel@gmail.com>]

On 2/23/2022 7:47 PM, Kirill A. Shutemov wrote:
> On Wed, Feb 23, 2022 at 07:02:49PM +0800, Tianyu Lan wrote:
>> On 2/23/2022 6:56 PM, Borislav Petkov wrote:
>>> On Wed, Feb 23, 2022 at 06:43:40PM +0800, Tianyu Lan wrote:
>>>> Hyper-V code check cpuid during runtime and there is no Hyper-V
>>>> isolation VM option.
>>>
>>> So how does "Current Hyper-V Isolation VM requires AMD_MEM_ENCRYPT" work
>>> exactly?
>>>
>>> Please explain in detail and not in piecemeal sentences.
>>>
>> The kernel in the image needs to select AMD_MEM_ENCRYPT option
>> otherwise the kernel can't boot up due to missing SEV support and
>> sev_es_ghcb_hv_call() always return error.
> 
> If kernel boots under SEV, doesn't it mean we have 'sme_me_mask'
> initialized? If it is non zero hv_is_isolation_supported() check in
> cc_platform_has() has zero effect as it checked after 'sme_me_mask'.
> 
> I still have no idea what is going on.
> 
> How SEV related to HyperV isolation? How detection happens? Could you
> give full picture?
> 

Hi Kriil:
      Current Hyper-V Isolation VM is unenlightened VM design. Hyper-V 
hides SEV capability from Linux guest and expose Hyper-V cpuid to show 
Hyper-V isolation VM capability. So sme_me_mask is zero in this case 
because SEV capability cpuid returns not-support.
      Hyper-V Isolation VM code uses some SEV API sev_es_ghcb_hv_call() 
to share code and so it's necessary to select AMD_MEM_ENCRYPT option for
Hyper-V Isolation VM.