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Message-ID: <9004ac7b-2df5-42c3-b3af-729ef5107822@arm.com>
Date: Thu, 1 May 2025 14:44:52 +0100
From: Steven Price <steven.price@....com>
To: Gavin Shan <gshan@...hat.com>, kvm@...r.kernel.org, kvmarm@...ts.linux.dev
Cc: Catalin Marinas <catalin.marinas@....com>, Marc Zyngier <maz@...nel.org>,
Will Deacon <will@...nel.org>, James Morse <james.morse@....com>,
Oliver Upton <oliver.upton@...ux.dev>,
Suzuki K Poulose <suzuki.poulose@....com>, Zenghui Yu
<yuzenghui@...wei.com>, linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org, Joey Gouly <joey.gouly@....com>,
Alexandru Elisei <alexandru.elisei@....com>,
Christoffer Dall <christoffer.dall@....com>, Fuad Tabba <tabba@...gle.com>,
linux-coco@...ts.linux.dev,
Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>,
Shanker Donthineni <sdonthineni@...dia.com>, Alper Gun
<alpergun@...gle.com>, "Aneesh Kumar K . V" <aneesh.kumar@...nel.org>
Subject: Re: [PATCH v8 06/43] arm64: RME: Define the user ABI
Hi Gavin,
On 30/04/2025 05:25, Gavin Shan wrote:
> On 4/16/25 11:41 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@....com>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
>> Signed-off-by: Steven Price <steven.price@....com>
>> ---
>> 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 | 70 +++++++++++++++++++++++++++++++
>> arch/arm64/include/uapi/asm/kvm.h | 49 ++++++++++++++++++++++
>> include/uapi/linux/kvm.h | 10 +++++
>> 3 files changed, 129 insertions(+)
>>
>
> With below comment addressed:
>
> Reviewed-by: Gavin Shan <gshan@...hat.com>
>
>> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/
>> api.rst
>> index 1f8625b7646a..99ba6c82cf37 100644
>> --- a/Documentation/virt/kvm/api.rst
>> +++ b/Documentation/virt/kvm/api.rst
>> @@ -3527,6 +3527,11 @@ Possible features:
>> - the KVM_REG_ARM64_SVE_VLS pseudo-register is immutable,
>> and can
>> no longer be written using KVM_SET_ONE_REG.
>> + - 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
>> -----------------------------
>> @@ -5098,6 +5103,7 @@ 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.
>> @@ -6452,6 +6458,30 @@ 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:
>> @@ -8280,6 +8310,46 @@ aforementioned registers before the first
>> KVM_RUN. These registers are VM
>> scoped, meaning that the same set of values are presented on all
>> vCPUs in a
>> given VM.
>> +7.38 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.
>> +: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 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_init_ripas 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 activate the realm. No
>> + further changes can be made to the
>> realm's
>> + configuration, and VCPUs are not
>> permitted to
>> + enter the realm until it has been
>> activated.
>
> ^^^^^^^^^^^^^^^^^^
> s/has been activated/is deactivated
I think I worded it badly before (as Susuki has already pointed out) and
you haven't understood what I intended.
VCPUs can be added to a Realm guest up until the ACTIVATE_REALM call.
There is no "deactivate" - you would need to destroy the guest and start
again.
What I intended was to say that a VCPU must not be executed (KVM_RUN)
until the ACTIVE_REALM call.
> I don't see where the guard is applied to prevent vCPU is added after realm
> has been activated. I may missed that. Otherwise, it's something to be
> improved
> n the subsequent patch where a vCPU is created and added to the realm.
This is handled in kvm_create_rec() where there's a check that
kvm_realm_state() != REALM_STATE_NEW. This prevents finalization of a
VCPU unless the realm is still in "new" state.
Admittedly this doesn't technically stop the user creating a VCPU. I
could add a check in kvm_arch_vcpu_create(), however this wouldn't stop
a VMM creating a VCPU and not finalising it before activating the realm.
So we'd end up with the same situation. I'm not sure whether it's worth
trying to stop the VMM or if I should just reword to say that the VMM
shouldn't do this.
I don't believe anything bad will happen to the host in these situations
- you will just end up with a useless VCPU which cannot be run.
Thanks,
Steve
>> +=================================
>> =============================================
>> +
>> 8. Other capabilities.
>> ======================
>> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/
>> uapi/asm/kvm.h
>> index af9d9acaf997..b57712880605 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_MEASUREMENT_ALGO_SHA256 0
>> +#define ARM_RME_CONFIG_MEASUREMENT_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 b6ae8ad8934b..0b8479985581 100644
>> --- a/include/uapi/linux/kvm.h
>> +++ b/include/uapi/linux/kvm.h
>> @@ -930,6 +930,7 @@ struct kvm_enable_cap {
>> #define KVM_CAP_X86_APIC_BUS_CYCLES_NS 237
>> #define KVM_CAP_X86_GUEST_MODE 238
>> #define KVM_CAP_ARM_WRITABLE_IMP_ID_REGS 239
>> +#define KVM_CAP_ARM_RME 240
>> struct kvm_irq_routing_irqchip {
>> __u32 irqchip;
>> @@ -1582,4 +1583,13 @@ 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
>
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