Re: [PATCH v9 06/43] arm64: RME: Define the user ABI

[Gavin Shan <gshan@redhat.com>]

On 6/11/25 8:48 PM, Steven Price wrote:
> There is one (multiplexed) CAP which can be used to create, populate and
> then activate the realm.
> 
> Co-developed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Signed-off-by: Steven Price <steven.price@arm.com>
> ---
> Changes since v8:
>   * Minor improvements to documentation following review.
>   * Bump the magic numbers to avoid conflicts.
> Changes since v7:
>   * Add documentation of new ioctls
>   * Bump the magic numbers to avoid conflicts
> Changes since v6:
>   * Rename some of the symbols to make their usage clearer and avoid
>     repetition.
> Changes from v5:
>   * Actually expose the new VCPU capability (KVM_ARM_VCPU_REC) by bumping
>     KVM_VCPU_MAX_FEATURES - note this also exposes KVM_ARM_VCPU_HAS_EL2!
> ---
>   Documentation/virt/kvm/api.rst    | 73 ++++++++++++++++++++++++++++++-
>   arch/arm64/include/uapi/asm/kvm.h | 49 +++++++++++++++++++++
>   include/uapi/linux/kvm.h          | 10 +++++
>   3 files changed, 131 insertions(+), 1 deletion(-)
> 

With below nitpicks addressed:

Reviewed-by: Gavin Shan <gshan@redhat.com>

> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 1bd2d42e6424..65543289f75c 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -3542,6 +3542,11 @@ Possible features:
>   	  Depends on KVM_CAP_ARM_EL2_E2H0.
>   	  KVM_ARM_VCPU_HAS_EL2 must also be set.
>   
> +	- KVM_ARM_VCPU_REC: Allocate a REC (Realm Execution Context) for this
> +	  VCPU. This must be specified on all VCPUs created in a Realm VM.
> +	  Depends on KVM_CAP_ARM_RME.
> +	  Requires KVM_ARM_VCPU_FINALIZE(KVM_ARM_VCPU_REC).
> +
>   4.83 KVM_ARM_PREFERRED_TARGET
>   -----------------------------
>   
> @@ -5115,6 +5120,7 @@ Recognised values for feature:
>   
>     =====      ===========================================
>     arm64      KVM_ARM_VCPU_SVE (requires KVM_CAP_ARM_SVE)
> +  arm64      KVM_ARM_VCPU_REC (requires KVM_CAP_ARM_RME)
>     =====      ===========================================
>   
>   Finalizes the configuration of the specified vcpu feature.
> @@ -6469,6 +6475,30 @@ the capability to be present.
>   
>   `flags` must currently be zero.
>   
> +4.144 KVM_ARM_VCPU_RMM_PSCI_COMPLETE
> +------------------------------------
> +
> +:Capability: KVM_CAP_ARM_RME
> +:Architectures: arm64
> +:Type: vcpu ioctl
> +:Parameters: struct kvm_arm_rmm_psci_complete (in)
> +:Returns: 0 if successful, < 0 on error
> +
> +::
> +
> +  struct kvm_arm_rmm_psci_complete {
> +	__u64 target_mpidr;
> +	__u32 psci_status;
> +	__u32 padding[3];
> +  };
> +
> +Where PSCI functions are handled by user space, the RMM needs to be informed of
> +the target of the operation using `target_mpidr`, along with the status
> +(`psci_status`). The RMM v1.0 specification defines two functions that require
> +this call: PSCI_CPU_ON and PSCI_AFFINITY_INFO.
> +
> +If the kernel is handling PSCI then this is done automatically and the VMM
> +doesn't need to call this ioctl.
>   
>   .. _kvm_run:
>   
> @@ -8528,7 +8558,7 @@ ENOSYS for the others.
>   When enabled, KVM will exit to userspace with KVM_EXIT_SYSTEM_EVENT of
>   type KVM_SYSTEM_EVENT_SUSPEND to process the guest suspend request.
>   
> -7.37 KVM_CAP_ARM_WRITABLE_IMP_ID_REGS
> +7.42 KVM_CAP_ARM_WRITABLE_IMP_ID_REGS
>   -------------------------------------
>   
>   :Architectures: arm64
> @@ -8557,6 +8587,47 @@ given VM.
>   When this capability is enabled, KVM resets the VCPU when setting
>   MP_STATE_INIT_RECEIVED through IOCTL.  The original MP_STATE is preserved.
>   
> +7.44 KVM_CAP_ARM_RME
> +--------------------
> +
> +:Architectures: arm64
> +:Target: VM
> +:Parameters: args[0] provides an action, args[1] points to a structure in
> +	     memory for some actions.
           ^^^
           Alignment

s/for some actions/for the action

> +:Returns: 0 on success, negative value on error
> +
> +Used to configure and set up the memory for a Realm. The available actions are:
> +
> +================================= =============================================
> + KVM_CAP_ARM_RME_CONFIG_REALM     Takes struct arm_rme_config as args[1] and
> +                                  configures realm parameters prior to it being
> +                                  created.
> +
> +                                  Options are ARM_RME_CONFIG_RPV to set the
> +                                  "Realm Personalization Value" and
> +                                  ARM_RME_CONFIG_HASH_ALGO to set the hash
> +                                  algorithm.
> +
> + KVM_CAP_ARM_RME_CREATE_REALM     Request the RMM to create the realm. The
> +                                  realm's configuration parameters must be set
> +                                  first.
> +
> + KVM_CAP_ARM_RME_INIT_RIPAS_REALM Takes struct arm_rme_init_ripas as args[1]
> +                                  and sets the RIPAS (Realm IPA State) to
> +                                  RIPAS_RAM of a specified area of the realm's
> +                                  IPA.
> +
> + KVM_CAP_ARM_RME_POPULATE_REALM   Takes struct arm_rme_populate_realm as
> +                                  args[1] and populates a region of protected
> +                                  address space by copying the data from the
> +                                  shared alias.
> +
> + KVM_CAP_ARM_RME_ACTIVATE_REALM   Request the RMM to activate the realm. No
> +                                  changes can be made to the Realm's memory,
> +                                  IPA state or configuration parameters.  No
> +                                  new VCPUs should be created after this step.
> +================================= =============================================
> +

The description about KVM_CAP_ARM_RME_ACTIVATE_REALM looks a bit confusing, maybe
something as below is more clear:

KVM_CAP_ARM_RME_ACTIVATE_REALM     Request the RMM to activate the realm. No changes
                                    can be made to the Realm's populated memory, IPA state,
                                    configuration parameters or vCPU addition after this
                                    step.

>   8. Other capabilities.
>   ======================
>   
> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
> index ed5f3892674c..9b5d67ecbc5e 100644
> --- a/arch/arm64/include/uapi/asm/kvm.h
> +++ b/arch/arm64/include/uapi/asm/kvm.h
> @@ -106,6 +106,7 @@ struct kvm_regs {
>   #define KVM_ARM_VCPU_PTRAUTH_GENERIC	6 /* VCPU uses generic authentication */
>   #define KVM_ARM_VCPU_HAS_EL2		7 /* Support nested virtualization */
>   #define KVM_ARM_VCPU_HAS_EL2_E2H0	8 /* Limit NV support to E2H RES0 */
> +#define KVM_ARM_VCPU_REC		9 /* VCPU REC state as part of Realm */
>   
>   struct kvm_vcpu_init {
>   	__u32 target;
> @@ -429,6 +430,54 @@ enum {
>   #define   KVM_DEV_ARM_VGIC_SAVE_PENDING_TABLES	3
>   #define   KVM_DEV_ARM_ITS_CTRL_RESET		4
>   
> +/* KVM_CAP_ARM_RME on VM fd */
> +#define KVM_CAP_ARM_RME_CONFIG_REALM		0
> +#define KVM_CAP_ARM_RME_CREATE_REALM		1
> +#define KVM_CAP_ARM_RME_INIT_RIPAS_REALM	2
> +#define KVM_CAP_ARM_RME_POPULATE_REALM		3
> +#define KVM_CAP_ARM_RME_ACTIVATE_REALM		4
> +
> +/* List of configuration items accepted for KVM_CAP_ARM_RME_CONFIG_REALM */
> +#define ARM_RME_CONFIG_RPV			0
> +#define ARM_RME_CONFIG_HASH_ALGO		1
> +
> +#define ARM_RME_CONFIG_HASH_ALGO_SHA256		0
> +#define ARM_RME_CONFIG_HASH_ALGO_SHA512		1
> +
> +#define ARM_RME_CONFIG_RPV_SIZE 64
> +
> +struct arm_rme_config {
> +	__u32 cfg;
> +	union {
> +		/* cfg == ARM_RME_CONFIG_RPV */
> +		struct {
> +			__u8	rpv[ARM_RME_CONFIG_RPV_SIZE];
> +		};
> +
> +		/* cfg == ARM_RME_CONFIG_HASH_ALGO */
> +		struct {
> +			__u32	hash_algo;
> +		};
> +
> +		/* Fix the size of the union */
> +		__u8	reserved[256];
> +	};
> +};
> +
> +#define KVM_ARM_RME_POPULATE_FLAGS_MEASURE	(1 << 0)
> +struct arm_rme_populate_realm {
> +	__u64 base;
> +	__u64 size;
> +	__u32 flags;
> +	__u32 reserved[3];
> +};
> +
> +struct arm_rme_init_ripas {
> +	__u64 base;
> +	__u64 size;
> +	__u64 reserved[2];
> +};
> +
>   /* Device Control API on vcpu fd */
>   #define KVM_ARM_VCPU_PMU_V3_CTRL	0
>   #define   KVM_ARM_VCPU_PMU_V3_IRQ		0
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index d00b85cb168c..3690664e272c 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -934,6 +934,7 @@ struct kvm_enable_cap {
>   #define KVM_CAP_ARM_EL2 240
>   #define KVM_CAP_ARM_EL2_E2H0 241
>   #define KVM_CAP_RISCV_MP_STATE_RESET 242
> +#define KVM_CAP_ARM_RME 243
>   
>   struct kvm_irq_routing_irqchip {
>   	__u32 irqchip;
> @@ -1586,4 +1587,13 @@ struct kvm_pre_fault_memory {
>   	__u64 padding[5];
>   };
>   
> +/* Available with KVM_CAP_ARM_RME, only for VMs with KVM_VM_TYPE_ARM_REALM  */
> +struct kvm_arm_rmm_psci_complete {
> +	__u64 target_mpidr;
> +	__u32 psci_status;
> +	__u32 padding[3];
> +};
> +
> +#define KVM_ARM_VCPU_RMM_PSCI_COMPLETE	_IOW(KVMIO, 0xd6, struct kvm_arm_rmm_psci_complete)
> +
>   #endif /* __LINUX_KVM_H */

Thanks,
Gavin