Re: [PATCH v3 12/27] KVM: arm64: Enable GICv3 Group-1 sysreg trapping via command-line

[Christoffer Dall <cdall@linaro.org>]

On Fri, Jun 09, 2017 at 12:49:41PM +0100, Marc Zyngier wrote:
> Now that we're able to safely handle Group-1 sysreg access, let's
> give the user the opportunity to enable it by passing a specific
> command-line option (vgic_v3.group1_trap).
> 
> Tested-by: Alexander Graf <agraf@suse.de>
> Acked-by: David Daney <david.daney@cavium.com>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

Acked-by: Christoffer Dall <cdall@linaro.org>

> ---
>  Documentation/admin-guide/kernel-parameters.txt |  4 ++++
>  virt/kvm/arm/vgic/vgic-v3.c                     | 11 +++++++++++
>  2 files changed, 15 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 15f79c27748d..42fe395be6c8 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1829,6 +1829,10 @@
>  			for all guests.
>  			Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
>  
> +	kvm-arm.vgic_v3_group1_trap=
> +			[KVM,ARM] Trap guest accesses to GICv3 group-1
> +			system registers
> +
>  	kvm-intel.ept=	[KVM,Intel] Disable extended page tables
>  			(virtualized MMU) support on capable Intel chips.
>  			Default is 1 (enabled)
> diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-v3.c
> index fbd678bc046d..df55818f095c 100644
> --- a/virt/kvm/arm/vgic/vgic-v3.c
> +++ b/virt/kvm/arm/vgic/vgic-v3.c
> @@ -416,6 +416,12 @@ int vgic_v3_map_resources(struct kvm *kvm)
>  
>  DEFINE_STATIC_KEY_FALSE(vgic_v3_cpuif_trap);
>  
> +static int __init early_group1_trap_cfg(char *buf)
> +{
> +	return strtobool(buf, &group1_trap);
> +}
> +early_param("kvm-arm.vgic_v3_group1_trap", early_group1_trap_cfg);
> +
>  /**
>   * vgic_v3_probe - probe for a GICv3 compatible interrupt controller in DT
>   * @node:	pointer to the DT node
> @@ -467,6 +473,11 @@ int vgic_v3_probe(const struct gic_kvm_info *info)
>  	if (kvm_vgic_global_state.vcpu_base == 0)
>  		kvm_info("disabling GICv2 emulation\n");
>  
> +	if (group1_trap) {
> +		kvm_info("GICv3 sysreg trapping enabled (reduced performance)\n");
> +		static_branch_enable(&vgic_v3_cpuif_trap);
> +	}
> +
>  	kvm_vgic_global_state.vctrl_base = NULL;
>  	kvm_vgic_global_state.type = VGIC_V3;
>  	kvm_vgic_global_state.max_gic_vcpus = VGIC_V3_MAX_CPUS;
> -- 
> 2.11.0
>