Re: [RFC PATCH v7 28/28] KVM: arm64: Allow the creation of a SPE enabled VM

[Alexandru Elisei <alexandru.elisei@arm.com>]

Hi Sashiko,

On Thu, Sep 03, 2026 at 04:59:29PM +0000, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] The Kconfig dependency for `KVM_ARM_SPE` restricts it to 'n' when the `ARM_SPE_PMU` driver is built as a module, preventing users from enabling SPE virtualization.
> --
> 
> commit 9bb804f4572dd230ad3b5db909bd2001b3ee3186
> Author: Alexandru Elisei <alexandru.elisei@arm.com>
> 
> KVM: arm64: Allow the creation of a SPE enabled VM
> 
> This commit introduces the Kconfig option KVM_ARM_SPE to allow userspace
> to enable the Statistical Profiling Extension (SPE) for virtual machines.
> 
> [ ... ]
> 
> > diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> > --- a/arch/arm64/kvm/Kconfig
> > +++ b/arch/arm64/kvm/Kconfig
> > @@ -106,9 +106,9 @@ endif # NVHE_EL2_DEBUG
> >  
> >  
> >  config KVM_ARM_SPE
> > -	bool
> > +	bool "Support SPE in guest"
> >  	depends on KVM && ARM_SPE_PMU
> 
> [Severity: Medium]
> Does this Kconfig dependency unintentionally disable KVM_ARM_SPE when the
> host driver ARM_SPE_PMU is built as a module?

That contradicts my experience. Setting CONFIG_ARM_SPE_PMU=m makes
CONFIG_KVM_ARM_SPE selectable, and building Linux with CONFIG_ARM_SPE_PMU=m and
CONFIG_KVM_ARM_SPE=y enables the SPE KVM capability when the SPE module is
loaded, and disables the capability when the module is removed.

Thanks,
Alex

> 
> Because KVM_ARM_SPE is a boolean, if ARM_SPE_PMU is configured as a
> loadable module (=m), the Kconfig dependency evaluates to m. For a boolean
> config, this restricts its maximum value to n, effectively disabling the
> feature in the build configuration.
> 
> Since the implementation in arch/arm64/kvm/spe.c supports being built
> against a modular driver (using try_module_get()), should this dependency
> be relaxed or handled differently so the feature can still be selected?
> 
> > -	default n
> > +	default y
> >  	help
> >  	  Adds support for Statistical Profiling Extension (SPE) in virtual
> >  	  machines.
> 
> -- 
> Sashiko AI review · https://sashiko.dev/#/patchset/20260903160623.315525-1-alexandru.elisei@arm.com?part=28