linux-kernel - Re: [PATCH v17 02/24] KVM: x86: Have all vendor neutral sub-configs depend on KVM

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Message-ID: <CA+EHjTx7OF2i4MvviAXQq0v6+a7T4SMU0PGsObDBo98Y6zvrBQ@mail.gmail.com>
Date: Thu, 31 Jul 2025 09:08:33 +0100
From: Fuad Tabba <tabba@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, Marc Zyngier <maz@...nel.org>, 
	Oliver Upton <oliver.upton@...ux.dev>, kvm@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, Ira Weiny <ira.weiny@...el.com>, 
	Gavin Shan <gshan@...hat.com>, Shivank Garg <shivankg@....com>, Vlastimil Babka <vbabka@...e.cz>, 
	Xiaoyao Li <xiaoyao.li@...el.com>, David Hildenbrand <david@...hat.com>, 
	Ackerley Tng <ackerleytng@...gle.com>, Tao Chan <chentao@...inos.cn>, 
	James Houghton <jthoughton@...gle.com>
Subject: Re: [PATCH v17 02/24] KVM: x86: Have all vendor neutral sub-configs
 depend on KVM_X86, not just KVM

On Tue, 29 Jul 2025 at 23:55, Sean Christopherson <seanjc@...gle.com> wrote:
>
> Make all vendor neutral KVM x86 configs depend on KVM_X86, not just KVM,
> i.e. gate them on at least one vendor module being enabled and thus on
> kvm.ko actually being built.  Depending on just KVM allows the user to
> select the configs even though they won't actually take effect, and more
> importantly, makes it all too easy to create unmet dependencies.  E.g.
> KVM_GENERIC_PRIVATE_MEM can't be selected by KVM_SW_PROTECTED_VM, because
> the KVM_GENERIC_MMU_NOTIFIER dependency is select by KVM_X86.
>
> Hiding all sub-configs when neither KVM_AMD nor KVM_INTEL is selected also
> helps communicate to the user that nothing "interesting" is going on, e.g.
>
>   --- Virtualization
>   <M>   Kernel-based Virtual Machine (KVM) support
>   < >   KVM for Intel (and compatible) processors support
>   < >   KVM for AMD processors support
>
> Fixes: ea4290d77bda ("KVM: x86: leave kvm.ko out of the build if no vendor module is requested")
> Reviewed-by: David Hildenbrand <david@...hat.com>
> Reviewed-by: Xiaoyao Li <xiaoyao.li@...el.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---


Reviewed-by: Fuad Tabba <tabba@...gle.com>

Cheers,
/fuad

>  arch/x86/kvm/Kconfig | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index 2c86673155c9..9895fc3cd901 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -74,7 +74,7 @@ config KVM_WERROR
>         # FRAME_WARN, i.e. KVM_WERROR=y with KASAN=y requires special tuning.
>         # Building KVM with -Werror and KASAN is still doable via enabling
>         # the kernel-wide WERROR=y.
> -       depends on KVM && ((EXPERT && !KASAN) || WERROR)
> +       depends on KVM_X86 && ((EXPERT && !KASAN) || WERROR)
>         help
>           Add -Werror to the build flags for KVM.
>
> @@ -83,7 +83,7 @@ config KVM_WERROR
>  config KVM_SW_PROTECTED_VM
>         bool "Enable support for KVM software-protected VMs"
>         depends on EXPERT
> -       depends on KVM && X86_64
> +       depends on KVM_X86 && X86_64
>         help
>           Enable support for KVM software-protected VMs.  Currently, software-
>           protected VMs are purely a development and testing vehicle for
> @@ -169,7 +169,7 @@ config KVM_AMD_SEV
>  config KVM_IOAPIC
>         bool "I/O APIC, PIC, and PIT emulation"
>         default y
> -       depends on KVM
> +       depends on KVM_X86
>         help
>           Provides support for KVM to emulate an I/O APIC, PIC, and PIT, i.e.
>           for full in-kernel APIC emulation.
> @@ -179,7 +179,7 @@ config KVM_IOAPIC
>  config KVM_SMM
>         bool "System Management Mode emulation"
>         default y
> -       depends on KVM
> +       depends on KVM_X86
>         help
>           Provides support for KVM to emulate System Management Mode (SMM)
>           in virtual machines.  This can be used by the virtual machine
> @@ -189,7 +189,7 @@ config KVM_SMM
>
>  config KVM_HYPERV
>         bool "Support for Microsoft Hyper-V emulation"
> -       depends on KVM
> +       depends on KVM_X86
>         default y
>         help
>           Provides KVM support for emulating Microsoft Hyper-V.  This allows KVM
> @@ -203,7 +203,7 @@ config KVM_HYPERV
>
>  config KVM_XEN
>         bool "Support for Xen hypercall interface"
> -       depends on KVM
> +       depends on KVM_X86
>         help
>           Provides KVM support for the hosting Xen HVM guests and
>           passing Xen hypercalls to userspace.
> @@ -213,7 +213,7 @@ config KVM_XEN
>  config KVM_PROVE_MMU
>         bool "Prove KVM MMU correctness"
>         depends on DEBUG_KERNEL
> -       depends on KVM
> +       depends on KVM_X86
>         depends on EXPERT
>         help
>           Enables runtime assertions in KVM's MMU that are too costly to enable
> @@ -228,7 +228,7 @@ config KVM_EXTERNAL_WRITE_TRACKING
>
>  config KVM_MAX_NR_VCPUS
>         int "Maximum number of vCPUs per KVM guest"
> -       depends on KVM
> +       depends on KVM_X86
>         range 1024 4096
>         default 4096 if MAXSMP
>         default 1024
> --
> 2.50.1.552.g942d659e1b-goog
>