linux-kernel - Re: [PATCH hyperv-next v5 03/11] Drivers: hv: Enable VTL mode for arm64

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Message-Id: <e0f81049-688e-4f53-a002-5d246281bf8d@app.fastmail.com>
Date: Sat, 08 Mar 2025 22:05:24 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Roman Kisel" <romank@...ux.microsoft.com>, bhelgaas@...gle.com,
 "Borislav Petkov" <bp@...en8.de>,
 "Catalin Marinas" <catalin.marinas@....com>,
 "Conor Dooley" <conor+dt@...nel.org>,
 "Dave Hansen" <dave.hansen@...ux.intel.com>,
 "Dexuan Cui" <decui@...rosoft.com>,
 "Haiyang Zhang" <haiyangz@...rosoft.com>,
 "H. Peter Anvin" <hpa@...or.com>, "Joey Gouly" <joey.gouly@....com>,
 krzk+dt@...nel.org, Krzysztof Wilczyński <kw@...ux.com>,
 "K. Y. Srinivasan" <kys@...rosoft.com>, "Len Brown" <lenb@...nel.org>,
 "Lorenzo Pieralisi" <lpieralisi@...nel.org>,
 "Manivannan Sadhasivam" <manivannan.sadhasivam@...aro.org>,
 "Mark Rutland" <mark.rutland@....com>, "Marc Zyngier" <maz@...nel.org>,
 "Ingo Molnar" <mingo@...hat.com>,
 "Oliver Upton" <oliver.upton@...ux.dev>,
 "Rafael J . Wysocki" <rafael@...nel.org>,
 "Rob Herring" <robh@...nel.org>, ssengar@...ux.microsoft.com,
 "Sudeep Holla" <sudeep.holla@....com>,
 "Suzuki K Poulose" <suzuki.poulose@....com>,
 "Thomas Gleixner" <tglx@...utronix.de>, "Wei Liu" <wei.liu@...nel.org>,
 "Will Deacon" <will@...nel.org>, "Zenghui Yu" <yuzenghui@...wei.com>,
 devicetree@...r.kernel.org, kvmarm@...ts.linux.dev,
 linux-acpi@...r.kernel.org, Linux-Arch <linux-arch@...r.kernel.org>,
 linux-arm-kernel@...ts.infradead.org, linux-hyperv@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org, x86@...nel.org
Cc: apais@...rosoft.com, benhill@...rosoft.com, bperkins@...rosoft.com,
 sunilmut@...rosoft.com
Subject: Re: [PATCH hyperv-next v5 03/11] Drivers: hv: Enable VTL mode for arm64

On Fri, Mar 7, 2025, at 23:02, Roman Kisel wrote:
> @@ -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_64 || ARM64)
>  	depends on SMP
> +	select OF_EARLY_FLATTREE
> +	select OF
>  	default n
>  	help

Having the dependency below the top-level Kconfig entry feels a little
counterintuitive. You could flip that back as it was before by doing

      select HYPERV_VTL_MODE if !ACPI
      depends on ACPI || SMP

in the HYPERV option, leaving the dependency on HYPERV in
HYPERV_VTL_MODE.

Is OF_EARLY_FLATTREE actually needed on x86?

      Arnd