linux-kernel - RE: [PATCH hyperv-next v8 06/11] arm64, x86: hyperv: Report the VTL the system boots in

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Date: Thu, 17 Apr 2025 15:28:14 +0000
From: Michael Kelley <mhklinux@...look.com>
To: Roman Kisel <romank@...ux.microsoft.com>, "arnd@...db.de" <arnd@...db.de>,
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Subject: RE: [PATCH hyperv-next v8 06/11] arm64, x86: hyperv: Report the VTL
 the system boots in

From: Roman Kisel <romank@...ux.microsoft.com> Sent: Monday, April 14, 2025 3:47 PM
> 
> The hyperv guest code might run in various Virtual Trust Levels.
> 
> Report the level when the kernel boots in the non-default (0)
> one.
> 
> Signed-off-by: Roman Kisel <romank@...ux.microsoft.com>
> ---
>  arch/arm64/hyperv/mshyperv.c | 2 ++
>  arch/x86/hyperv/hv_vtl.c     | 7 ++++++-
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
> index 43f422a7ef34..4fdc26ade1d7 100644
> --- a/arch/arm64/hyperv/mshyperv.c
> +++ b/arch/arm64/hyperv/mshyperv.c
> @@ -118,6 +118,8 @@ static int __init hyperv_init(void)
>  	if (ms_hyperv.priv_high & HV_ACCESS_PARTITION_ID)
>  		hv_get_partition_id();
>  	ms_hyperv.vtl = get_vtl();
> +	if (ms_hyperv.vtl > 0) /* non default VTL */
> +		pr_info("Linux runs in Hyper-V Virtual Trust Level %d\n", ms_hyperv.vtl);
> 
>  	ms_hyperv_late_init();
> 
> diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
> index 582fe820e29c..038c896fdd60 100644
> --- a/arch/x86/hyperv/hv_vtl.c
> +++ b/arch/x86/hyperv/hv_vtl.c
> @@ -55,7 +55,12 @@ static void  __noreturn hv_vtl_restart(char __maybe_unused *cmd)
> 
>  void __init hv_vtl_init_platform(void)
>  {
> -	pr_info("Linux runs in Hyper-V Virtual Trust Level\n");
> +	/*
> +	 * This function is a no-op if the VTL mode is not enabled.
> +	 * If it is, this function runs if and only the kernel boots in
> +	 * VTL2 which the x86 hv initialization path makes sure of.
> +	 */
> +	pr_info("Linux runs in Hyper-V Virtual Trust Level %d\n", ms_hyperv.vtl);
> 
>  	x86_platform.realmode_reserve = x86_init_noop;
>  	x86_platform.realmode_init = x86_init_noop;
> --
> 2.43.0
> 

Reviewed-by: Michael Kelley <mhklinux@...look.com>