RE: [PATCH V6 2/5] x86/hyper-v: Add hyperv Isolation VM check in the cc_platform_has()

["Michael Kelley (LINUX)" <mikelley@microsoft.com>]

From: Tianyu Lan <ltykernel@gmail.com> Sent: Monday, December 6, 2021 11:56 PM
> 
> Hyper-V provides Isolation VM which has memory encrypt support. Add
> hyperv_cc_platform_has() and return true for check of GUEST_MEM_ENCRYPT
> attribute.
> 
> Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
> ---
> Change since v3:
> 	* Change code style of checking GUEST_MEM attribute in the
> 	  hyperv_cc_platform_has().
> ---
>  arch/x86/kernel/cc_platform.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/x86/kernel/cc_platform.c b/arch/x86/kernel/cc_platform.c
> index 03bb2f343ddb..47db88c275d5 100644
> --- a/arch/x86/kernel/cc_platform.c
> +++ b/arch/x86/kernel/cc_platform.c
> @@ -11,6 +11,7 @@
>  #include <linux/cc_platform.h>
>  #include <linux/mem_encrypt.h>
> 
> +#include <asm/mshyperv.h>
>  #include <asm/processor.h>
> 
>  static bool __maybe_unused intel_cc_platform_has(enum cc_attr attr)
> @@ -58,9 +59,16 @@ static bool amd_cc_platform_has(enum cc_attr attr)
>  #endif
>  }
> 
> +static bool hyperv_cc_platform_has(enum cc_attr attr)
> +{
> +	return attr == CC_ATTR_GUEST_MEM_ENCRYPT;
> +}
> 
>  bool cc_platform_has(enum cc_attr attr)
>  {
> +	if (hv_is_isolation_supported())
> +		return hyperv_cc_platform_has(attr);
> +
>  	if (sme_me_mask)
>  		return amd_cc_platform_has(attr);
> 

Throughout Linux kernel code, there are about 20 calls to cc_platform_has()
with CC_ATTR_GUEST_MEM_ENCRYPT as the argument.  The original code
(from v1 of this patch set) only dealt with the call in sev_setup_arch().   But
with this patch, all the other calls that previously returned "false" will now
return "true" in a Hyper-V Isolated VM.  I didn't try to analyze all these other
calls, so I think there's an open question about whether this is the behavior
we want.

Michael