Re: [PATCH V3 03/13] x86/HV: Add new hvcall guest address host visibility support

[Dave Hansen <dave.hansen@intel.com>]

On 8/9/21 10:56 AM, Tianyu Lan wrote:
> From: Tianyu Lan <Tianyu.Lan@microsoft.com>
> 
> Add new hvcall guest address host visibility support to mark
> memory visible to host. Call it inside set_memory_decrypted
> /encrypted(). Add HYPERVISOR feature check in the
> hv_is_isolation_supported() to optimize in non-virtualization
> environment.

From an x86/mm perspective:

Acked-by: Dave Hansen <dave.hansen@intel.com>

A tiny nit:

> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index 0bb4d9ca7a55..b3683083208a 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -607,6 +607,12 @@ EXPORT_SYMBOL_GPL(hv_get_isolation_type);
>  
>  bool hv_is_isolation_supported(void)
>  {
> +	if (!cpu_feature_enabled(X86_FEATURE_HYPERVISOR))
> +		return 0;
> +
> +	if (!hypervisor_is_type(X86_HYPER_MS_HYPERV))
> +		return 0;
> +
>  	return hv_get_isolation_type() != HV_ISOLATION_TYPE_NONE;
>  }
This might be worthwhile to move to a header.  That ensures that
hv_is_isolation_supported() use can avoid even a function call.  But, I
see this is used in modules and its use here is also in a slow path, so
it's not a big deal