linux-kernel - RE: [PATCH hyperv-next v4 2/6] Drivers: hv: Enable VTL mode for arm64

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Date: Wed, 19 Feb 2025 23:14:42 +0000
From: Michael Kelley <mhklinux@...look.com>
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Subject: RE: [PATCH hyperv-next v4 2/6] Drivers: hv: Enable VTL mode for arm64

From: Roman Kisel <romank@...ux.microsoft.com> Sent: Tuesday, February 11, 2025 5:43 PM
> 
> Kconfig dependencies for arm64 guests on Hyper-V require that be
> ACPI enabled, and limit VTL mode to x86/x64. To enable VTL mode
> on arm64 as well, update the dependencies. Since VTL mode requires
> DeviceTree instead of ACPI, don't require arm64 guests on Hyper-V
> to have ACPI unconditionally.
> 
> Signed-off-by: Roman Kisel <romank@...ux.microsoft.com>
> ---
>  drivers/hv/Kconfig | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/hv/Kconfig b/drivers/hv/Kconfig
> index 862c47b191af..db9912ef96a8 100644
> --- a/drivers/hv/Kconfig
> +++ b/drivers/hv/Kconfig
> @@ -5,18 +5,20 @@ menu "Microsoft Hyper-V guest support" config HYPERV
>  	tristate "Microsoft Hyper-V client drivers"
>  	depends on (X86 && X86_LOCAL_APIC && HYPERVISOR_GUEST) \
> -		|| (ACPI && ARM64 && !CPU_BIG_ENDIAN)
> +		|| (ARM64 && !CPU_BIG_ENDIAN)
> +	depends on (ACPI || HYPERV_VTL_MODE)
>  	select PARAVIRT
>  	select X86_HV_CALLBACK_VECTOR if X86
> -	select OF_EARLY_FLATTREE if OF
>  	help
>  	  Select this option to run Linux as a Hyper-V client operating
>  	  system.
> 
>  config HYPERV_VTL_MODE
>  	bool "Enable Linux to boot in VTL context"
> -	depends on X86_64 && HYPERV
> +	depends on (X86 || ARM64)

Any reason to choose "X86" instead of "X86_64"? I can't
imagine VTL mode making any sense for 32-bit, but maybe
I'm wrong! :-)

>  	depends on SMP
> +	select OF_EARLY_FLATTREE
> +	select OF
>  	default n
>  	help
>  	  Virtual Secure Mode (VSM) is a set of hypervisor capabilities and
> @@ -31,7 +33,7 @@ config HYPERV_VTL_MODE
> 
>  	  Select this option to build a Linux kernel to run at a VTL other than
>  	  the normal VTL0, which currently is only VTL2.  This option
> -	  initializes the x86 platform for VTL2, and adds the ability to boot
> +	  initializes the kernel to run in VTL2, and adds the ability to boot
>  	  secondary CPUs directly into 64-bit context as required for VTLs other
>  	  than 0.  A kernel built with this option must run at VTL2, and will
>  	  not run as a normal guest.
> --
> 2.43.0
>