Re: [PATCH v8 13/43] arm64: RME: Support for the VGIC in realms

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 16/04/2025 14:41, Steven Price wrote:
> The RMM provides emulation of a VGIC to the realm guest but delegates
> much of the handling to the host. Implement support in KVM for
> saving/restoring state to/from the REC structure.
> 
> Signed-off-by: Steven Price <steven.price@arm.com>
> ---
> Changes from v5:
>   * Handle RMM providing fewer GIC LRs than the hardware supports.
> ---
>   arch/arm64/include/asm/kvm_rme.h |  1 +
>   arch/arm64/kvm/arm.c             | 16 +++++++++---
>   arch/arm64/kvm/rme.c             |  5 ++++
>   arch/arm64/kvm/vgic/vgic-init.c  |  2 +-
>   arch/arm64/kvm/vgic/vgic-v3.c    |  6 ++++-
>   arch/arm64/kvm/vgic/vgic.c       | 43 ++++++++++++++++++++++++++++++--
>   6 files changed, 66 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_rme.h b/arch/arm64/include/asm/kvm_rme.h
> index f716b890e484..9bcad6ec5dbb 100644
> --- a/arch/arm64/include/asm/kvm_rme.h
> +++ b/arch/arm64/include/asm/kvm_rme.h
> @@ -92,6 +92,7 @@ struct realm_rec {
>   
>   void kvm_init_rme(void);
>   u32 kvm_realm_ipa_limit(void);
> +u32 kvm_realm_vgic_nr_lr(void);
>   
>   int kvm_realm_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap);
>   int kvm_init_realm_vm(struct kvm *kvm);
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index fd83efb667cc..808d7e479571 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -683,19 +683,24 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
>   		kvm_call_hyp_nvhe(__pkvm_vcpu_put);
>   	}
>   
> +	kvm_timer_vcpu_put(vcpu);
> +	kvm_vgic_put(vcpu);
> +
> +	vcpu->cpu = -1;
> +
> +	if (vcpu_is_rec(vcpu))
> +		return;
> +
>   	kvm_vcpu_put_debug(vcpu);
>   	kvm_arch_vcpu_put_fp(vcpu);
>   	if (has_vhe())
>   		kvm_vcpu_put_vhe(vcpu);
> -	kvm_timer_vcpu_put(vcpu);
> -	kvm_vgic_put(vcpu);
>   	kvm_vcpu_pmu_restore_host(vcpu);
>   	if (vcpu_has_nv(vcpu))
>   		kvm_vcpu_put_hw_mmu(vcpu);
>   	kvm_arm_vmid_clear_active();
>   
>   	vcpu_clear_on_unsupported_cpu(vcpu);
> -	vcpu->cpu = -1;
>   }
>   
>   static void __kvm_arm_vcpu_power_off(struct kvm_vcpu *vcpu)
> @@ -912,6 +917,11 @@ int kvm_arch_vcpu_run_pid_change(struct kvm_vcpu *vcpu)
>   			return ret;
>   	}
>   
> +	if (!irqchip_in_kernel(kvm) && kvm_is_realm(vcpu->kvm)) {
> +		/* Userspace irqchip not yet supported with Realms */
> +		return -EOPNOTSUPP;
> +	}
> +
>   	mutex_lock(&kvm->arch.config_lock);
>   	set_bit(KVM_ARCH_FLAG_HAS_RAN_ONCE, &kvm->arch.flags);
>   	mutex_unlock(&kvm->arch.config_lock);
> diff --git a/arch/arm64/kvm/rme.c b/arch/arm64/kvm/rme.c
> index f4923fc3b34e..1239eb07aca6 100644
> --- a/arch/arm64/kvm/rme.c
> +++ b/arch/arm64/kvm/rme.c
> @@ -77,6 +77,11 @@ u32 kvm_realm_ipa_limit(void)
>   	return u64_get_bits(rmm_feat_reg0, RMI_FEATURE_REGISTER_0_S2SZ);
>   }
>   
> +u32 kvm_realm_vgic_nr_lr(void)
> +{
> +	return u64_get_bits(rmm_feat_reg0, RMI_FEATURE_REGISTER_0_GICV3_NUM_LRS);
> +}
> +
>   static int get_start_level(struct realm *realm)
>   {
>   	return 4 - ((realm->ia_bits - 8) / (RMM_PAGE_SHIFT - 3));
> diff --git a/arch/arm64/kvm/vgic/vgic-init.c b/arch/arm64/kvm/vgic/vgic-init.c
> index 1f33e71c2a73..a81c7f3d1d42 100644
> --- a/arch/arm64/kvm/vgic/vgic-init.c
> +++ b/arch/arm64/kvm/vgic/vgic-init.c
> @@ -81,7 +81,7 @@ int kvm_vgic_create(struct kvm *kvm, u32 type)
>   	 * the proper checks already.
>   	 */
>   	if (type == KVM_DEV_TYPE_ARM_VGIC_V2 &&
> -		!kvm_vgic_global_state.can_emulate_gicv2)
> +	    (!kvm_vgic_global_state.can_emulate_gicv2 || kvm_is_realm(kvm)))
>   		return -ENODEV;
>   
>   	/* Must be held to avoid race with vCPU creation */
> diff --git a/arch/arm64/kvm/vgic/vgic-v3.c b/arch/arm64/kvm/vgic/vgic-v3.c
> index b9ad7c42c5b0..c10ad817030d 100644
> --- a/arch/arm64/kvm/vgic/vgic-v3.c
> +++ b/arch/arm64/kvm/vgic/vgic-v3.c
> @@ -8,9 +8,11 @@
>   #include <linux/kvm_host.h>
>   #include <linux/string_choices.h>
>   #include <kvm/arm_vgic.h>
> +#include <asm/kvm_emulate.h>
>   #include <asm/kvm_hyp.h>
>   #include <asm/kvm_mmu.h>
>   #include <asm/kvm_asm.h>
> +#include <asm/rmi_smc.h>
>   
>   #include "vgic.h"
>   
> @@ -758,7 +760,9 @@ void vgic_v3_put(struct kvm_vcpu *vcpu)
>   		return;
>   	}
>   
> -	if (likely(!is_protected_kvm_enabled()))
> +	if (vcpu_is_rec(vcpu))
> +		cpu_if->vgic_vmcr = vcpu->arch.rec.run->exit.gicv3_vmcr;
> +	else if (likely(!is_protected_kvm_enabled()))
>   		kvm_call_hyp(__vgic_v3_save_vmcr_aprs, cpu_if);
>   	WARN_ON(vgic_v4_put(vcpu));
>   
> diff --git a/arch/arm64/kvm/vgic/vgic.c b/arch/arm64/kvm/vgic/vgic.c
> index 8d189ce18ea0..c68a41a29917 100644
> --- a/arch/arm64/kvm/vgic/vgic.c
> +++ b/arch/arm64/kvm/vgic/vgic.c
> @@ -10,7 +10,9 @@
>   #include <linux/list_sort.h>
>   #include <linux/nospec.h>
>   
> +#include <asm/kvm_emulate.h>
>   #include <asm/kvm_hyp.h>
> +#include <asm/kvm_rme.h>
>   
>   #include "vgic.h"
>   
> @@ -23,6 +25,8 @@ struct vgic_global kvm_vgic_global_state __ro_after_init = {
>   
>   static inline int kvm_vcpu_vgic_nr_lr(struct kvm_vcpu *vcpu)
>   {
> +	if (unlikely(vcpu_is_rec(vcpu)))
> +		return kvm_realm_vgic_nr_lr();
>   	return kvm_vgic_global_state.nr_lr;
>   }
>   
> @@ -864,10 +868,23 @@ static inline bool can_access_vgic_from_kernel(void)
>   	return !static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif) || has_vhe();
>   }
>   
> +static inline void vgic_rmm_save_state(struct kvm_vcpu *vcpu)
> +{
> +	struct vgic_v3_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v3;
> +	int i;
> +
> +	for (i = 0; i < kvm_vcpu_vgic_nr_lr(vcpu); i++) {
> +		cpu_if->vgic_lr[i] = vcpu->arch.rec.run->exit.gicv3_lrs[i];
> +		vcpu->arch.rec.run->enter.gicv3_lrs[i] = 0;
> +	}
> +}

We also need to save/restore gicv3_hcr/cpuif->vgic_hcr.

> +
>   static inline void vgic_save_state(struct kvm_vcpu *vcpu)
>   {
>   	if (!static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif))
>   		vgic_v2_save_state(vcpu);
> +	else if (vcpu_is_rec(vcpu))
> +		vgic_rmm_save_state(vcpu);
>   	else
>   		__vgic_v3_save_state(&vcpu->arch.vgic_cpu.vgic_v3);
>   }
> @@ -903,10 +920,28 @@ void kvm_vgic_sync_hwstate(struct kvm_vcpu *vcpu)
>   	vgic_prune_ap_list(vcpu);
>   }
>   
> +static inline void vgic_rmm_restore_state(struct kvm_vcpu *vcpu)
> +{
> +	struct vgic_v3_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v3;
> +	int i;
> +
> +	for (i = 0; i < kvm_vcpu_vgic_nr_lr(vcpu); i++) {
> +		vcpu->arch.rec.run->enter.gicv3_lrs[i] = cpu_if->vgic_lr[i];
> +		/*
> +		 * Also populate the rec.run->exit copies so that a late
> +		 * decision to back out from entering the realm doesn't cause
> +		 * the state to be lost
> +		 */
> +		vcpu->arch.rec.run->exit.gicv3_lrs[i] = cpu_if->vgic_lr[i];
> +	}
> +}
> +
>   static inline void vgic_restore_state(struct kvm_vcpu *vcpu)
>   {
>   	if (!static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif))
>   		vgic_v2_restore_state(vcpu);
> +	else if (vcpu_is_rec(vcpu))
> +		vgic_rmm_restore_state(vcpu);
>   	else
>   		__vgic_v3_restore_state(&vcpu->arch.vgic_cpu.vgic_v3);
>   }
> @@ -976,7 +1011,9 @@ void kvm_vgic_flush_hwstate(struct kvm_vcpu *vcpu)
>   
>   void kvm_vgic_load(struct kvm_vcpu *vcpu)
>   {
> -	if (unlikely(!irqchip_in_kernel(vcpu->kvm) || !vgic_initialized(vcpu->kvm))) {
> +	if (unlikely(!irqchip_in_kernel(vcpu->kvm) ||
> +		     !vgic_initialized(vcpu->kvm) ||
> +		     vcpu_is_rec(vcpu))) {


>   		if (has_vhe() && static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif))
>   			__vgic_v3_activate_traps(&vcpu->arch.vgic_cpu.vgic_v3);
>   		return;
> @@ -990,7 +1027,9 @@ void kvm_vgic_load(struct kvm_vcpu *vcpu)
>   
>   void kvm_vgic_put(struct kvm_vcpu *vcpu)
>   {
> -	if (unlikely(!irqchip_in_kernel(vcpu->kvm) || !vgic_initialized(vcpu->kvm))) {
> +	if (unlikely(!irqchip_in_kernel(vcpu->kvm) ||
> +		     !vgic_initialized(vcpu->kvm) ||
> +		     vcpu_is_rec(vcpu))) {
>   		if (has_vhe() && static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif))
>   			__vgic_v3_deactivate_traps(&vcpu->arch.vgic_cpu.vgic_v3);

We could return early here for rec, and skip the unnecessary trap steps. 
Similar for the vgic_load case.

Rest looks good to me.

Suzuki


>   		return;