Re: [PATCH v13 07/48] arm64: RMI: Check for RMI support at KVM init

[Wei-Lin Chang]

On Wed, Mar 18, 2026 at 03:53:31PM +0000, Steven Price wrote:
> Query the RMI version number and check if it is a compatible version. A
> static key is also provided to signal that a supported RMM is available.
> 
> Functions are provided to query if a VM or VCPU is a realm (or rec)
> which currently will always return false.
> 
> Later patches make use of struct realm and the states as the ioctls
> interfaces are added to support realm and REC creation and destruction.
> 
> Signed-off-by: Steven Price <steven.price@xxxxxxx>
> ---
> Changes since v12:
>  * Drop check for 4k page size.
> Changes since v11:
>  * Reword slightly the comments on the realm states.
> Changes since v10:
>  * kvm_is_realm() no longer has a NULL check.
>  * Rename from "rme" to "rmi" when referring to the RMM interface.
>  * Check for RME (hardware) support before probing for RMI support.
> Changes since v8:
>  * No need to guard kvm_init_rme() behind 'in_hyp_mode'.
> Changes since v6:
>  * Improved message for an unsupported RMI ABI version.
> Changes since v5:
>  * Reword "unsupported" message from "host supports" to "we want" to
>    clarify that 'we' are the 'host'.
> Changes since v2:
>  * Drop return value from kvm_init_rme(), it was always 0.
>  * Rely on the RMM return value to identify whether the RSI ABI is
>    compatible.
> ---
>  arch/arm64/include/asm/kvm_emulate.h | 18 +++++++++
>  arch/arm64/include/asm/kvm_host.h    |  4 ++
>  arch/arm64/include/asm/kvm_rmi.h     | 56 +++++++++++++++++++++++++++
>  arch/arm64/include/asm/virt.h        |  1 +
>  arch/arm64/kernel/cpufeature.c       |  1 +
>  arch/arm64/kvm/Makefile              |  2 +-
>  arch/arm64/kvm/arm.c                 |  5 +++
>  arch/arm64/kvm/rmi.c                 | 57 ++++++++++++++++++++++++++++
>  8 files changed, 143 insertions(+), 1 deletion(-)
>  create mode 100644 arch/arm64/include/asm/kvm_rmi.h
>  create mode 100644 arch/arm64/kvm/rmi.c
> 
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index 5bf3d7e1d92c..f38b50151ce8 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -688,4 +688,22 @@ static inline void vcpu_set_hcrx(struct kvm_vcpu *vcpu)
>  			vcpu->arch.hcrx_el2 |= HCRX_EL2_EnASR;
>  	}
>  }
> +
> +static inline bool kvm_is_realm(struct kvm *kvm)
> +{
> +	if (static_branch_unlikely(&kvm_rmi_is_available))
> +		return kvm->arch.is_realm;
> +	return false;
> +}
> +
> +static inline enum realm_state kvm_realm_state(struct kvm *kvm)
> +{
> +	return READ_ONCE(kvm->arch.realm.state);
> +}
> +
> +static inline bool vcpu_is_rec(struct kvm_vcpu *vcpu)
> +{
> +	return false;
> +}
> +

Hi,

Both kvm_vm_is_protected() and vcpu_is_protected() are in kvm_host.h, do
you think that's a better place? Or is there a reason for this being in
kvm_emulate.h?

Thanks,
Wei-Lin Chang

>  #endif /* __ARM64_KVM_EMULATE_H__ */
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 5d5a3bbdb95e..9267a2f2d65b 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -27,6 +27,7 @@
>  #include <asm/fpsimd.h>
>  #include <asm/kvm.h>
>  #include <asm/kvm_asm.h>
> +#include <asm/kvm_rmi.h>
>  #include <asm/vncr_mapping.h>
>  
>  #define __KVM_HAVE_ARCH_INTC_INITIALIZED
> @@ -405,6 +406,9 @@ struct kvm_arch {
>  	 * the associated pKVM instance in the hypervisor.
>  	 */
>  	struct kvm_protected_vm pkvm;
> +
> +	bool is_realm;
> +	struct realm realm;
>  };
>  
>  struct kvm_vcpu_fault_info {
> diff --git a/arch/arm64/include/asm/kvm_rmi.h b/arch/arm64/include/asm/kvm_rmi.h
> new file mode 100644
> index 000000000000..3506f50b05cd
> --- /dev/null
> +++ b/arch/arm64/include/asm/kvm_rmi.h
> @@ -0,0 +1,56 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2023-2025 ARM Ltd.
> + */
> +
> +#ifndef __ASM_KVM_RMI_H
> +#define __ASM_KVM_RMI_H
> +
> +/**
> + * enum realm_state - State of a Realm
> + */
> +enum realm_state {
> +	/**
> +	 * @REALM_STATE_NONE:
> +	 *      Realm has not yet been created. rmi_realm_create() has not
> +	 *      yet been called.
> +	 */
> +	REALM_STATE_NONE,
> +	/**
> +	 * @REALM_STATE_NEW:
> +	 *      Realm is under construction, rmi_realm_create() has been
> +	 *      called, but it is not yet activated. Pages may be populated.
> +	 */
> +	REALM_STATE_NEW,
> +	/**
> +	 * @REALM_STATE_ACTIVE:
> +	 *      Realm has been created and is eligible for execution with
> +	 *      rmi_rec_enter(). Pages may no longer be populated with
> +	 *      rmi_data_create().
> +	 */
> +	REALM_STATE_ACTIVE,
> +	/**
> +	 * @REALM_STATE_DYING:
> +	 *      Realm is in the process of being destroyed or has already been
> +	 *      destroyed.
> +	 */
> +	REALM_STATE_DYING,
> +	/**
> +	 * @REALM_STATE_DEAD:
> +	 *      Realm has been destroyed.
> +	 */
> +	REALM_STATE_DEAD
> +};
> +
> +/**
> + * struct realm - Additional per VM data for a Realm
> + *
> + * @state: The lifetime state machine for the realm
> + */
> +struct realm {
> +	enum realm_state state;
> +};
> +
> +void kvm_init_rmi(void);
> +
> +#endif /* __ASM_KVM_RMI_H */
> diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
> index b51ab6840f9c..dc9b2899e0b2 100644
> --- a/arch/arm64/include/asm/virt.h
> +++ b/arch/arm64/include/asm/virt.h
> @@ -87,6 +87,7 @@ void __hyp_reset_vectors(void);
>  bool is_kvm_arm_initialised(void);
>  
>  DECLARE_STATIC_KEY_FALSE(kvm_protected_mode_initialized);
> +DECLARE_STATIC_KEY_FALSE(kvm_rmi_is_available);
>  
>  static inline bool is_pkvm_initialized(void)
>  {
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index c31f8e17732a..ddf7e57f23e8 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -289,6 +289,7 @@ static const struct arm64_ftr_bits ftr_id_aa64isar3[] = {
>  static const struct arm64_ftr_bits ftr_id_aa64pfr0[] = {
>  	ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_EL1_CSV3_SHIFT, 4, 0),
>  	ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_EL1_CSV2_SHIFT, 4, 0),
> +	ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_EL1_RME_SHIFT, 4, 0),
>  	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_EL1_DIT_SHIFT, 4, 0),
>  	ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_EL1_AMU_SHIFT, 4, 0),
>  	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_EL1_MPAM_SHIFT, 4, 0),
> diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
> index 3ebc0570345c..e17c4077d8e7 100644
> --- a/arch/arm64/kvm/Makefile
> +++ b/arch/arm64/kvm/Makefile
> @@ -16,7 +16,7 @@ CFLAGS_handle_exit.o += -Wno-override-init
>  kvm-y += arm.o mmu.o mmio.o psci.o hypercalls.o pvtime.o \
>  	 inject_fault.o va_layout.o handle_exit.o config.o \
>  	 guest.o debug.o reset.o sys_regs.o stacktrace.o \
> -	 vgic-sys-reg-v3.o fpsimd.o pkvm.o \
> +	 vgic-sys-reg-v3.o fpsimd.o pkvm.o rmi.o \
>  	 arch_timer.o trng.o vmid.o emulate-nested.o nested.o at.o \
>  	 vgic/vgic.o vgic/vgic-init.o \
>  	 vgic/vgic-irqfd.o vgic/vgic-v2.o \
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 29f0326f7e00..274d7866efdc 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -39,6 +39,7 @@
>  #include <asm/kvm_nested.h>
>  #include <asm/kvm_pkvm.h>
>  #include <asm/kvm_ptrauth.h>
> +#include <asm/kvm_rmi.h>
>  #include <asm/sections.h>
>  #include <asm/stacktrace/nvhe.h>
>  
> @@ -104,6 +105,8 @@ long kvm_get_cap_for_kvm_ioctl(unsigned int ioctl, long *ext)
>  	return -EINVAL;
>  }
>  
> +DEFINE_STATIC_KEY_FALSE(kvm_rmi_is_available);
> +
>  DECLARE_KVM_HYP_PER_CPU(unsigned long, kvm_hyp_vector);
>  
>  DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_base);
> @@ -2921,6 +2924,8 @@ static __init int kvm_arm_init(void)
>  
>  	in_hyp_mode = is_kernel_in_hyp_mode();
>  
> +	kvm_init_rmi();
> +
>  	if (cpus_have_final_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE) ||
>  	    cpus_have_final_cap(ARM64_WORKAROUND_1508412))
>  		kvm_info("Guests without required CPU erratum workarounds can deadlock system!\n" \
> diff --git a/arch/arm64/kvm/rmi.c b/arch/arm64/kvm/rmi.c
> new file mode 100644
> index 000000000000..fac151580c01
> --- /dev/null
> +++ b/arch/arm64/kvm/rmi.c
> @@ -0,0 +1,57 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2023-2025 ARM Ltd.
> + */
> +
> +#include <linux/kvm_host.h>
> +
> +#include <asm/rmi_cmds.h>
> +#include <asm/virt.h>
> +
> +static int rmi_check_version(void)
> +{
> +	struct arm_smccc_res res;
> +	unsigned short version_major, version_minor;
> +	unsigned long host_version = RMI_ABI_VERSION(RMI_ABI_MAJOR_VERSION,
> +						     RMI_ABI_MINOR_VERSION);
> +	unsigned long aa64pfr0 = read_sanitised_ftr_reg(SYS_ID_AA64PFR0_EL1);
> +
> +	/* If RME isn't supported, then RMI can't be */
> +	if (cpuid_feature_extract_unsigned_field(aa64pfr0, ID_AA64PFR0_EL1_RME_SHIFT) == 0)
> +		return -ENXIO;
> +
> +	arm_smccc_1_1_invoke(SMC_RMI_VERSION, host_version, &res);
> +
> +	if (res.a0 == SMCCC_RET_NOT_SUPPORTED)
> +		return -ENXIO;
> +
> +	version_major = RMI_ABI_VERSION_GET_MAJOR(res.a1);
> +	version_minor = RMI_ABI_VERSION_GET_MINOR(res.a1);
> +
> +	if (res.a0 != RMI_SUCCESS) {
> +		unsigned short high_version_major, high_version_minor;
> +
> +		high_version_major = RMI_ABI_VERSION_GET_MAJOR(res.a2);
> +		high_version_minor = RMI_ABI_VERSION_GET_MINOR(res.a2);
> +
> +		kvm_err("Unsupported RMI ABI (v%d.%d - v%d.%d) we want v%d.%d\n",
> +			version_major, version_minor,
> +			high_version_major, high_version_minor,
> +			RMI_ABI_MAJOR_VERSION,
> +			RMI_ABI_MINOR_VERSION);
> +		return -ENXIO;
> +	}
> +
> +	kvm_info("RMI ABI version %d.%d\n", version_major, version_minor);
> +
> +	return 0;
> +}
> +
> +void kvm_init_rmi(void)
> +{
> +	/* Continue without realm support if we can't agree on a version */
> +	if (rmi_check_version())
> +		return;
> +
> +	/* Future patch will enable static branch kvm_rmi_is_available */
> +}
> -- 
> 2.43.0
>