Re: [PATCH kvmtool v4 15/15] arm64: smccc: Start sending PSCI to userspace

[Marc Zyngier <maz@kernel.org>]

On Tue, 30 Sep 2025 11:31:30 +0100,
Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
> 
> From: Oliver Upton <oliver.upton@linux.dev>
> 
> kvmtool now has a PSCI implementation that complies with v1.0 of the
> specification. Use the SMCCC filter to start sending these calls out to
> userspace for further handling. While at it, shut the door on the
> legacy, KVM-specific v0.1 functions.
> 
> Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> ---
>  arm64/include/kvm/kvm-config-arch.h |  8 +++++--
>  arm64/smccc.c                       | 37 +++++++++++++++++++++++++++++
>  2 files changed, 43 insertions(+), 2 deletions(-)
> 
> diff --git a/arm64/include/kvm/kvm-config-arch.h b/arm64/include/kvm/kvm-config-arch.h
> index ee031f01..3158fadf 100644
> --- a/arm64/include/kvm/kvm-config-arch.h
> +++ b/arm64/include/kvm/kvm-config-arch.h
> @@ -15,6 +15,7 @@ struct kvm_config_arch {
>  	u64		fw_addr;
>  	unsigned int	sve_max_vq;
>  	bool		no_pvtime;
> +	bool		in_kernel_smccc;
>  };
>  
>  int irqchip_parser(const struct option *opt, const char *arg, int unset);
> @@ -52,11 +53,14 @@ int sve_vl_parser(const struct option *opt, const char *arg, int unset);
>  			   "Force virtio devices to use PCI as their default "	\
>  			   "transport (Deprecated: Use --virtio-transport "	\
>  			   "option instead)", virtio_transport_parser, kvm),	\
> -        OPT_CALLBACK('\0', "irqchip", &(cfg)->irqchip,				\
> +	OPT_CALLBACK('\0', "irqchip", &(cfg)->irqchip,				\
>  		     "[gicv2|gicv2m|gicv3|gicv3-its]",				\
>  		     "Type of interrupt controller to emulate in the guest",	\
>  		     irqchip_parser, NULL),					\
>  	OPT_U64('\0', "firmware-address", &(cfg)->fw_addr,			\
> -		"Address where firmware should be loaded"),
> +		"Address where firmware should be loaded"),			\
> +	OPT_BOOLEAN('\0', "in-kernel-smccc", &(cfg)->in_kernel_smccc,		\
> +			"Disable userspace handling of SMCCC, instead"		\
> +			" relying on the in-kernel implementation"),
>

nit: this really is about PSCI, not SMCCC. The fact that we use the
SMCCC interface to route PSCI calls is an implementation detail,
really. The other thing is that this is a change in default behaviour,
and I'd rather keep in-kernel PSCI to be the default, specially given
that this otherwise silently fails on old kernels.

To that effect, I'd suggest the following instead:

+	OPT_BOOLEAN('\0', "psci", &(cfg)->userspace_psci,		\
+			"Request userspace handling of PSCI, instead"		\
+			" relying on the in-kernel implementation"),

and the code modified accordingly.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.