linux-kernel - Re: [PATCH 1/2] KVM: x86: leave kvm.ko out of the build if no vendor module is requested

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Message-ID: <Zv_0GzOkrPVCRfP1@google.com>
Date: Fri, 4 Oct 2024 07:27:49 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org, 
	torvalds@...ux-foundation.org
Subject: Re: [PATCH 1/2] KVM: x86: leave kvm.ko out of the build if no vendor
 module is requested

On Thu, Oct 03, 2024, Paolo Bonzini wrote:
> kvm.ko is nothing but library code shared by kvm-intel.ko and kvm-amd.ko.
> It provides no functionality on its own and it is unnecessary unless one
> of the vendor-specific module is compiled.  In particular, /dev/kvm is
> not created until one of kvm-intel.ko or kvm-amd.ko is loaded.
> 
> Use CONFIG_KVM to decide if it is built-in or a module, but use the
> vendor-specific modules for the actual decision on whether to build it.
> 
> This also fixes a build failure when CONFIG_KVM_INTEL and CONFIG_KVM_AMD
> are both disabled.  The cpu_emergency_register_virt_callback() function
> is called from kvm.ko, but it is only defined if at least one of
> CONFIG_KVM_INTEL and CONFIG_KVM_AMD is provided.
> 
> Fixes: 590b09b1d88e ("KVM: x86: Register "emergency disable" callbacks when virt is enabled")
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/Kconfig  | 7 +++++--
>  arch/x86/kvm/Makefile | 2 +-
>  2 files changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index 730c2f34d347..81bce9dd9331 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -17,8 +17,8 @@ menuconfig VIRTUALIZATION
>  
>  if VIRTUALIZATION
>  
> -config KVM
> -	tristate "Kernel-based Virtual Machine (KVM) support"
> +config KVM_X86_COMMON

Maybe just KVM_X86?  I doubt anyone in KVM will care too much, and for the rest
of the kernel, CONFIG_KVM_X86 is likely more intuitive than CONFIG_KVM_X86_COMMON.