Re: [PATCH v8 05/43] arm64: RME: Check for RME support at KVM init

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

On 16/04/2025 14:41, 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@arm.com>
> Reviewed-by: Gavin Shan <gshan@redhat.com>
> ---
> 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              |  3 +-
>   arch/arm64/kvm/arm.c                 |  6 +++
>   arch/arm64/kvm/rme.c                 | 56 ++++++++++++++++++++++++++++
>   7 files changed, 143 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 d7cf66573aca..1c43a4fc25dd 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -686,4 +686,22 @@ static inline void vcpu_set_hcrx(struct kvm_vcpu *vcpu)
>   			vcpu->arch.hcrx_el2 |= HCRX_EL2_EnFPM;
>   	}
>   }
> +
> +static inline bool kvm_is_realm(struct kvm *kvm)
> +{
> +	if (static_branch_unlikely(&kvm_rme_is_available) && kvm)
> +		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 e98cfe7855a6..7bd81b86eab0 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
> @@ -394,6 +395,9 @@ 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_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
> +
> +/**
> + * 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 ebf4a9f943ed..e45d47156dcf 100644
> --- a/arch/arm64/include/asm/virt.h
> +++ b/arch/arm64/include/asm/virt.h
> @@ -81,6 +81,7 @@ 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);
>   
>   static inline bool is_pkvm_initialized(void)
>   {
> diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
> index 209bc76263f1..2ebc66812d49 100644
> --- a/arch/arm64/kvm/Makefile
> +++ b/arch/arm64/kvm/Makefile
> @@ -23,7 +23,8 @@ kvm-y += arm.o mmu.o mmio.o psci.o hypercalls.o pvtime.o \
>   	 vgic/vgic-v3.o vgic/vgic-v4.o \
>   	 vgic/vgic-mmio.o vgic/vgic-mmio-v2.o \
>   	 vgic/vgic-mmio-v3.o vgic/vgic-kvm-device.o \
> -	 vgic/vgic-its.o vgic/vgic-debug.o vgic/vgic-v3-nested.o
> +	 vgic/vgic-its.o vgic/vgic-debug.o vgic/vgic-v3-nested.o \
> +	 rme.o
>   
>   kvm-$(CONFIG_HW_PERF_EVENTS)  += pmu-emul.o pmu.o
>   kvm-$(CONFIG_ARM64_PTR_AUTH)  += pauth.o
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 68fec8c95fee..856a721d41ac 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);
> @@ -2819,6 +2822,9 @@ static __init int kvm_arm_init(void)
>   
>   	in_hyp_mode = is_kernel_in_hyp_mode();
>   
> +	if (in_hyp_mode)
> +		kvm_init_rme();
> +

minor nit:

I wondering if this check is necessary. If the host is running under a
a hypervisor, it could relay the calls to the RMM. Nothing urgent, but
it is a possibility. It doesn't matter to the host as such. The
Realm Guest will do its own verification and the host can ignore
what lies beneath ?


Either ways,

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>