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

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Message-ID: <e0dce529-0777-491d-aced-1e9ead31ac17@linux.microsoft.com>
Date: Mon, 10 Mar 2025 10:35:05 -0700
From: Roman Kisel <romank@...ux.microsoft.com>
To: Arnd Bergmann <arnd@...db.de>, Michael Kelley <mhklinux@...look.com>
Cc: apais@...rosoft.com, benhill@...rosoft.com, bperkins@...rosoft.com,
 sunilmut@...rosoft.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
Subject: Re: [PATCH hyperv-next v5 03/11] Drivers: hv: Enable VTL mode for
 arm64

On 3/8/2025 1:05 PM, Arnd Bergmann wrote:
> 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.
> 

I was implementing Michael's suggestion, and might've gone a bit
overboard, my bad. I'll fix this, thanks a lot for reviewing!

> Is OF_EARLY_FLATTREE actually needed on x86?
> 

No, it is not needed on x86. It is only needed when VTL mode is used.

>        Arnd

-- 
Thank you,
Roman