Subject: Re: [PATCH v10 05/43] arm64: RME: Check for RME support at KVM init

From: Marc Zyngier <[email-masked]>
Date: Wed, 01 Oct 2025 12:05:58 +0100

On Wed, 20 Aug 2025 15:55:25 +0100,
Steven Price <[email-masked]> 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.
> 
> Reviewed-by: Gavin Shan <[email-masked]>
> Reviewed-by: Suzuki K Poulose <[email-masked]>
> Signed-off-by: Steven Price <[email-masked]>
> ---
> 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_rme.h     | 56 ++++++++++++++++++++++++++++
>  arch/arm64/include/asm/virt.h        |  1 +
>  arch/arm64/kvm/Makefile              |  2 +-
>  arch/arm64/kvm/arm.c                 |  5 +++
>  arch/arm64/kvm/rme.c                 | 56 ++++++++++++++++++++++++++++
>  7 files changed, 141 insertions(+), 1 deletion(-)
>  create mode 100644 arch/arm64/include/asm/kvm_rme.h
>  create mode 100644 arch/arm64/kvm/rme.c
> 
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index fa8a08a1ccd5..ab4093e41c4b 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -674,4 +674,22 @@ static inline void vcpu_set_hcrx(struct kvm_vcpu *vcpu)
>  			vcpu->arch.hcrx_el2 |= HCRX_EL2_SCTLR2En;
>  	}
>  }
> +
> +static inline bool kvm_is_realm(struct kvm *kvm)
> +{
> +	if (static_branch_unlikely(&kvm_rme_is_available) && kvm)

Under what circumstances would you call this with a NULL pointer?

> +		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;
> +}
> +
>  #endif /* __ARM64_KVM_EMULATE_H__ */
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 2f2394cce24e..d1511ce26191 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_rme.h>
>  #include <asm/vncr_mapping.h>
>  
>  #define __KVM_HAVE_ARCH_INTC_INITIALIZED
> @@ -404,6 +405,9 @@ struct kvm_arch {
>  	 * the associated pKVM instance in the hypervisor.
>  	 */
>  	struct kvm_protected_vm pkvm;
> +
> +	bool is_realm;
> +	struct realm realm;

Given that pkvm and CCA are pretty much exclusive, I don't think we
need to store both states separately. Make those a union.

>  };
>  
>  struct kvm_vcpu_fault_info {
> diff --git a/arch/arm64/include/asm/kvm_rme.h b/arch/arm64/include/asm/kvm_rme.h
> new file mode 100644
> index 000000000000..9c8a0b23e0e4
> --- /dev/null
> +++ b/arch/arm64/include/asm/kvm_rme.h
> @@ -0,0 +1,56 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2023 ARM Ltd.
> + */
> +
> +#ifndef __ASM_KVM_RME_H
> +#define __ASM_KVM_RME_H

None of that is about RME. This is about CCA, which is purely a SW
construct, and not a CPU architecture feature.

So 's/rme/cca/' everywhere that describe something that is not a
direct effect of FEAT_RME being implemented on the CPU, but instead
something that is CCA-specific.

> +
> +/**
> + * enum realm_state - State of a Realm
> + */
> +enum realm_state {
> +	/**
> +	 * @REALM_STATE_NONE:
> +	 *      Realm has not yet been created. rmi_realm_create() may be
> +	 *      called to create the realm.
> +	 */
> +	REALM_STATE_NONE,
> +	/**
> +	 * @REALM_STATE_NEW:
> +	 *      Realm is under construction, not eligible for execution. Pages
> +	 *      may be populated with rmi_data_create().
> +	 */
> +	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_rme(void);
> +
> +#endif /* __ASM_KVM_RME_H */
> diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
> index aa280f356b96..db73c9bfd8c9 100644
> --- a/arch/arm64/include/asm/virt.h
> +++ b/arch/arm64/include/asm/virt.h
> @@ -82,6 +82,7 @@ void __hyp_reset_vectors(void);
>  bool is_kvm_arm_initialised(void);
>  
>  DECLARE_STATIC_KEY_FALSE(kvm_protected_mode_initialized);
> +DECLARE_STATIC_KEY_FALSE(kvm_rme_is_available);

Same thing about RME.

>  
>  static inline bool is_pkvm_initialized(void)
>  {
> diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
> index 3ebc0570345c..70fa017831b3 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 rme.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 888f7c7abf54..76177c56f1ef 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -40,6 +40,7 @@
>  #include <asm/kvm_nested.h>
>  #include <asm/kvm_pkvm.h>
>  #include <asm/kvm_ptrauth.h>
> +#include <asm/kvm_rme.h>
>  #include <asm/sections.h>
>  
>  #include <kvm/arm_hypercalls.h>
> @@ -59,6 +60,8 @@ enum kvm_wfx_trap_policy {
>  static enum kvm_wfx_trap_policy kvm_wfi_trap_policy __read_mostly = KVM_WFX_NOTRAP_SINGLE_TASK;
>  static enum kvm_wfx_trap_policy kvm_wfe_trap_policy __read_mostly = KVM_WFX_NOTRAP_SINGLE_TASK;
>  
> +DEFINE_STATIC_KEY_FALSE(kvm_rme_is_available);
> +
>  DECLARE_KVM_HYP_PER_CPU(unsigned long, kvm_hyp_vector);
>  
>  DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_base);
> @@ -2836,6 +2839,8 @@ static __init int kvm_arm_init(void)
>  
>  	in_hyp_mode = is_kernel_in_hyp_mode();
>  
> +	kvm_init_rme();
> +
>  	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/rme.c b/arch/arm64/kvm/rme.c
> new file mode 100644
> index 000000000000..67cf2d94cb2d
> --- /dev/null
> +++ b/arch/arm64/kvm/rme.c
> @@ -0,0 +1,56 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2023 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);
> +
> +	arm_smccc_1_1_invoke(SMC_RMI_VERSION, host_version, &res);

Shouldn't you first check that RME is actually available, by looking
at ID_AA64PFR0_EL1.RME?

> +
> +	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_rme(void)
> +{
> +	if (PAGE_SIZE != SZ_4K)
> +		/* Only 4k page size on the host is supported */
> +		return;

Move the comment above the check (same thing below).

	M.

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