Subject: Re: [PATCH v5 15/36] KVM: arm64: gic-v5: Implement GICv5 load/put and save/restore

From: Marc Zyngier <[email-masked]>
Date: Wed, 04 Mar 2026 09:26:52 +0000

On Thu, 26 Feb 2026 15:59:18 +0000,
Sascha Bischoff <[email-masked]> wrote:
> 
> This change introduces GICv5 load/put. Additionally, it plumbs in
> save/restore for:
> 
> * PPIs (ICH_PPI_x_EL2 regs)
> * ICH_VMCR_EL2
> * ICH_APR_EL2
> * ICC_ICSR_EL1
> 
> A GICv5-specific enable bit is added to struct vgic_vmcr as this
> differs from previous GICs. On GICv5-native systems, the VMCR only
> contains the enable bit (driven by the guest via ICC_CR0_EL1.EN) and
> the priority mask (PCR).
> 
> A struct gicv5_vpe is also introduced. This currently only contains a
> single field - bool resident - which is used to track if a VPE is
> currently running or not, and is used to avoid a case of double load
> or double put on the WFI path for a vCPU. This struct will be extended
> as additional GICv5 support is merged, specifically for VPE doorbells.
> 
> Co-authored-by: Timothy Hayes <[email-masked]>
> Signed-off-by: Timothy Hayes <[email-masked]>
> Signed-off-by: Sascha Bischoff <[email-masked]>
> Reviewed-by: Jonathan Cameron <[email-masked]>
> ---
>  arch/arm64/kvm/hyp/nvhe/switch.c   | 12 +++++
>  arch/arm64/kvm/vgic/vgic-mmio.c    | 28 +++++++----
>  arch/arm64/kvm/vgic/vgic-v5.c      | 74 ++++++++++++++++++++++++++++++
>  arch/arm64/kvm/vgic/vgic.c         | 32 ++++++++-----
>  arch/arm64/kvm/vgic/vgic.h         |  7 +++
>  include/kvm/arm_vgic.h             |  2 +
>  include/linux/irqchip/arm-gic-v5.h |  5 ++
>  7 files changed, 141 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c
> index b41485ce295ab..a88da302b6d08 100644
> --- a/arch/arm64/kvm/hyp/nvhe/switch.c
> +++ b/arch/arm64/kvm/hyp/nvhe/switch.c
> @@ -113,6 +113,12 @@ static void __deactivate_traps(struct kvm_vcpu *vcpu)
>  /* Save VGICv3 state on non-VHE systems */
>  static void __hyp_vgic_save_state(struct kvm_vcpu *vcpu)
>  {
> +	if (vgic_is_v5(kern_hyp_va(vcpu->kvm))) {
> +		__vgic_v5_save_state(&vcpu->arch.vgic_cpu.vgic_v5);
> +		__vgic_v5_save_ppi_state(&vcpu->arch.vgic_cpu.vgic_v5);
> +		return;
> +	}
> +
>  	if (static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif)) {
>  		__vgic_v3_save_state(&vcpu->arch.vgic_cpu.vgic_v3);
>  		__vgic_v3_deactivate_traps(&vcpu->arch.vgic_cpu.vgic_v3);
> @@ -122,6 +128,12 @@ static void __hyp_vgic_save_state(struct kvm_vcpu *vcpu)
>  /* Restore VGICv3 state on non-VHE systems */
>  static void __hyp_vgic_restore_state(struct kvm_vcpu *vcpu)
>  {
> +	if (vgic_is_v5(kern_hyp_va(vcpu->kvm))) {
> +		__vgic_v5_restore_state(&vcpu->arch.vgic_cpu.vgic_v5);
> +		__vgic_v5_restore_ppi_state(&vcpu->arch.vgic_cpu.vgic_v5);
> +		return;
> +	}
> +
>  	if (static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif)) {
>  		__vgic_v3_activate_traps(&vcpu->arch.vgic_cpu.vgic_v3);
>  		__vgic_v3_restore_state(&vcpu->arch.vgic_cpu.vgic_v3);
> diff --git a/arch/arm64/kvm/vgic/vgic-mmio.c b/arch/arm64/kvm/vgic/vgic-mmio.c
> index a573b1f0c6cbe..675c2844f5e5c 100644
> --- a/arch/arm64/kvm/vgic/vgic-mmio.c
> +++ b/arch/arm64/kvm/vgic/vgic-mmio.c
> @@ -842,18 +842,30 @@ vgic_find_mmio_region(const struct vgic_register_region *regions,
>  
>  void vgic_set_vmcr(struct kvm_vcpu *vcpu, struct vgic_vmcr *vmcr)
>  {
> -	if (kvm_vgic_global_state.type == VGIC_V2)
> -		vgic_v2_set_vmcr(vcpu, vmcr);
> -	else
> -		vgic_v3_set_vmcr(vcpu, vmcr);
> +	const struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
> +
> +	if (dist->vgic_model == KVM_DEV_TYPE_ARM_VGIC_V5) {
> +		vgic_v5_set_vmcr(vcpu, vmcr);
> +	} else {
> +		if (kvm_vgic_global_state.type == VGIC_V2)
> +			vgic_v2_set_vmcr(vcpu, vmcr);
> +		else
> +			vgic_v3_set_vmcr(vcpu, vmcr);
> +	}

This looks rather ugly, and doesn't make use of the helpers you
introduced in patch #1. How about:

	switch (dist->vgic_model) {
	case KVM_DEV_TYPE_ARM_VGIC_V5:
		vgic_v5_set_vmcr(vcpu, vmcr);
		break;
	case KVM_DEV_TYPE_ARM_VGIC_V3:
		vgic_v3_set_vmcr(vcpu, vmcr);
		break;
	case KVM_DEV_TYPE_ARM_VGIC_V2:
		if (static_branch_likely(&kvm_vgic_global_state.gicv3_cpuif))
			vgic_v3_set_vmcr(vcpu, vmcr);
		else
			vgic_v2_set_vmcr(vcpu, vmcr);
		break;
	default:
		BUG();
	}

Yes, the handling of v3 is a bit redundant, but I find it overall more
readable.

>  }
>  
>  void vgic_get_vmcr(struct kvm_vcpu *vcpu, struct vgic_vmcr *vmcr)
>  {
> -	if (kvm_vgic_global_state.type == VGIC_V2)
> -		vgic_v2_get_vmcr(vcpu, vmcr);
> -	else
> -		vgic_v3_get_vmcr(vcpu, vmcr);
> +	const struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
> +
> +	if (dist->vgic_model == KVM_DEV_TYPE_ARM_VGIC_V5) {
> +		vgic_v5_get_vmcr(vcpu, vmcr);
> +	} else {
> +		if (kvm_vgic_global_state.type == VGIC_V2)
> +			vgic_v2_get_vmcr(vcpu, vmcr);
> +		else
> +			vgic_v3_get_vmcr(vcpu, vmcr);
> +	}
>  }
>  
>  /*
> diff --git a/arch/arm64/kvm/vgic/vgic-v5.c b/arch/arm64/kvm/vgic/vgic-v5.c
> index 2c51b9ba4f118..5b35c756887a9 100644
> --- a/arch/arm64/kvm/vgic/vgic-v5.c
> +++ b/arch/arm64/kvm/vgic/vgic-v5.c
> @@ -85,3 +85,77 @@ int vgic_v5_probe(const struct gic_kvm_info *info)
>  
>  	return 0;
>  }
> +
> +void vgic_v5_load(struct kvm_vcpu *vcpu)
> +{
> +	struct vgic_v5_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v5;
> +
> +	/*
> +	 * On the WFI path, vgic_load is called a second time. The first is when
> +	 * scheduling in the vcpu thread again, and the second is when leaving
> +	 * WFI. Skip the second instance as it serves no purpose and just
> +	 * restores the same state again.
> +	 */
> +	if (READ_ONCE(cpu_if->gicv5_vpe.resident))
> +		return;

I'm perplex. What is READ_ONCE()/WRITE_ONCE() guaranteeing?

> +
> +	kvm_call_hyp(__vgic_v5_restore_vmcr_apr, cpu_if);
> +
> +	WRITE_ONCE(cpu_if->gicv5_vpe.resident, true);
> +}
> +
> +void vgic_v5_put(struct kvm_vcpu *vcpu)
> +{
> +	struct vgic_v5_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v5;
> +
> +	/*
> +	 * Do nothing if we're not resident. This can happen in the WFI path
> +	 * where we do a vgic_put in the WFI path and again later when
> +	 * descheduling the thread. We risk losing VMCR state if we sync it
> +	 * twice, so instead return early in this case.
> +	 */
> +	if (!READ_ONCE(cpu_if->gicv5_vpe.resident))
> +		return;
> +
> +	kvm_call_hyp(__vgic_v5_save_apr, cpu_if);
> +
> +	WRITE_ONCE(cpu_if->gicv5_vpe.resident, false);
> +}
> +
> +void vgic_v5_get_vmcr(struct kvm_vcpu *vcpu, struct vgic_vmcr *vmcrp)
> +{
> +	struct vgic_v5_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v5;
> +	u64 vmcr = cpu_if->vgic_vmcr;
> +
> +	vmcrp->en = FIELD_GET(FEAT_GCIE_ICH_VMCR_EL2_EN, vmcr);
> +	vmcrp->pmr = FIELD_GET(FEAT_GCIE_ICH_VMCR_EL2_VPMR, vmcr);
> +}
> +
> +void vgic_v5_set_vmcr(struct kvm_vcpu *vcpu, struct vgic_vmcr *vmcrp)
> +{
> +	struct vgic_v5_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v5;
> +	u64 vmcr;
> +
> +	vmcr = FIELD_PREP(FEAT_GCIE_ICH_VMCR_EL2_VPMR, vmcrp->pmr) |
> +	       FIELD_PREP(FEAT_GCIE_ICH_VMCR_EL2_EN, vmcrp->en);
> +
> +	cpu_if->vgic_vmcr = vmcr;
> +}
> +
> +void vgic_v5_restore_state(struct kvm_vcpu *vcpu)
> +{
> +	struct vgic_v5_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v5;
> +
> +	__vgic_v5_restore_state(cpu_if);
> +	kvm_call_hyp(__vgic_v5_restore_ppi_state, cpu_if);
> +	dsb(sy);
> +}
> +
> +void vgic_v5_save_state(struct kvm_vcpu *vcpu)
> +{
> +	struct vgic_v5_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v5;
> +
> +	__vgic_v5_save_state(cpu_if);
> +	kvm_call_hyp(__vgic_v5_save_ppi_state, cpu_if);
> +	dsb(sy);
> +}
> diff --git a/arch/arm64/kvm/vgic/vgic.c b/arch/arm64/kvm/vgic/vgic.c
> index 2c0e8803342e2..1005ff5f36235 100644
> --- a/arch/arm64/kvm/vgic/vgic.c
> +++ b/arch/arm64/kvm/vgic/vgic.c
> @@ -996,7 +996,9 @@ static inline bool can_access_vgic_from_kernel(void)
>  
>  static inline void vgic_save_state(struct kvm_vcpu *vcpu)
>  {
> -	if (!static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif))
> +	if (vgic_is_v5(vcpu->kvm))
> +		vgic_v5_save_state(vcpu);
> +	else if (!static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif))
>  		vgic_v2_save_state(vcpu);
>  	else
>  		__vgic_v3_save_state(&vcpu->arch.vgic_cpu.vgic_v3);
> @@ -1005,14 +1007,16 @@ static inline void vgic_save_state(struct kvm_vcpu *vcpu)
>  /* Sync back the hardware VGIC state into our emulation after a guest's run. */
>  void kvm_vgic_sync_hwstate(struct kvm_vcpu *vcpu)
>  {
> -	/* If nesting, emulate the HW effect from L0 to L1 */
> -	if (vgic_state_is_nested(vcpu)) {
> -		vgic_v3_sync_nested(vcpu);
> -		return;
> -	}
> +	if (!vgic_is_v5(vcpu->kvm)) {

This should directly check for v3. Even once we add v5 support to NV,
I don't expect the code to be common at all.

> +		/* If nesting, emulate the HW effect from L0 to L1 */
> +		if (vgic_state_is_nested(vcpu)) {
> +			vgic_v3_sync_nested(vcpu);
> +			return;
> +		}
>  
> -	if (vcpu_has_nv(vcpu))
> -		vgic_v3_nested_update_mi(vcpu);
> +		if (vcpu_has_nv(vcpu))
> +			vgic_v3_nested_update_mi(vcpu);
> +	}
>  
>  	if (can_access_vgic_from_kernel())
>  		vgic_save_state(vcpu);
> @@ -1034,7 +1038,9 @@ void kvm_vgic_process_async_update(struct kvm_vcpu *vcpu)
>  
>  static inline void vgic_restore_state(struct kvm_vcpu *vcpu)
>  {
> -	if (!static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif))
> +	if (vgic_is_v5(vcpu->kvm))
> +		vgic_v5_restore_state(vcpu);
> +	else if (!static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif))
>  		vgic_v2_restore_state(vcpu);
>  	else
>  		__vgic_v3_restore_state(&vcpu->arch.vgic_cpu.vgic_v3);

I have similar comments as some the previous hunks. Using switch/case
statements would be more readable IMO.

Thanks,

	M.

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