Message-ID: <af65f499-8d31-96ed-3608-52225c879d8a@arm.com>
Date:   Fri, 10 Mar 2023 15:47:21 +0000
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Subject: Re: [RFC PATCH 06/28] arm64: RME: ioctls to create and configure
 realms
Content-Language: en-GB
To:     Zhi Wang <zhi.wang.linux@gmail.com>
Cc:     kvm@vger.kernel.org, kvmarm@lists.linux.dev,
        Catalin Marinas <catalin.marinas@arm.com>,
        Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>,
        James Morse <james.morse@arm.com>,
        Oliver Upton <oliver.upton@linux.dev>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Zenghui Yu <yuzenghui@huawei.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Joey Gouly <joey.gouly@arm.com>,
        Alexandru Elisei <alexandru.elisei@arm.com>,
        Christoffer Dall <christoffer.dall@arm.com>,
        Fuad Tabba <tabba@google.com>, linux-coco@lists.linux.dev
References: <20230127112248.136810-1-suzuki.poulose@arm.com>
 <20230127112932.38045-1-steven.price@arm.com>
 <20230127112932.38045-7-steven.price@arm.com>
 <20230306211015.0000129d@gmail.com>
From:   Steven Price <steven.price@arm.com>
In-Reply-To: <20230306211015.0000129d@gmail.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 06/03/2023 19:10, Zhi Wang wrote:
> On Fri, 27 Jan 2023 11:29:10 +0000
> Steven Price <steven.price@arm.com> wrote:
> 
>> Add the KVM_CAP_ARM_RME_CREATE_FD ioctl to create a realm. This involves
>> delegating pages to the RMM to hold the Realm Descriptor (RD) and for
>> the base level of the Realm Translation Tables (RTT). A VMID also need
>> to be picked, since the RMM has a separate VMID address space a
>> dedicated allocator is added for this purpose.
>>
>> KVM_CAP_ARM_RME_CONFIG_REALM is provided to allow configuring the realm
>> before it is created.
>>
>> Signed-off-by: Steven Price <steven.price@arm.com>
>> ---
>>  arch/arm64/include/asm/kvm_rme.h |  14 ++
>>  arch/arm64/kvm/arm.c             |  19 ++
>>  arch/arm64/kvm/mmu.c             |   6 +
>>  arch/arm64/kvm/reset.c           |  33 +++
>>  arch/arm64/kvm/rme.c             | 357 +++++++++++++++++++++++++++++++
>>  5 files changed, 429 insertions(+)
>>
>> diff --git a/arch/arm64/include/asm/kvm_rme.h b/arch/arm64/include/asm/kvm_rme.h
>> index c26bc2c6770d..055a22accc08 100644
>> --- a/arch/arm64/include/asm/kvm_rme.h
>> +++ b/arch/arm64/include/asm/kvm_rme.h
>> @@ -6,6 +6,8 @@
>>  #ifndef __ASM_KVM_RME_H
>>  #define __ASM_KVM_RME_H
>>  
>> +#include <uapi/linux/kvm.h>
>> +
>>  enum realm_state {
>>  	REALM_STATE_NONE,
>>  	REALM_STATE_NEW,
>> @@ -15,8 +17,20 @@ enum realm_state {
>>  
>>  struct realm {
>>  	enum realm_state state;
>> +
>> +	void *rd;
>> +	struct realm_params *params;
>> +
>> +	unsigned long num_aux;
>> +	unsigned int vmid;
>> +	unsigned int ia_bits;
>>  };
>>  
>>  int kvm_init_rme(void);
>> +u32 kvm_realm_ipa_limit(void);
>> +
>> +int kvm_realm_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap);
>> +int kvm_init_realm_vm(struct kvm *kvm);
>> +void kvm_destroy_realm(struct kvm *kvm);
>>  
>>  #endif
>> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
>> index d97b39d042ab..50f54a63732a 100644
>> --- a/arch/arm64/kvm/arm.c
>> +++ b/arch/arm64/kvm/arm.c
>> @@ -103,6 +103,13 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
>>  		r = 0;
>>  		set_bit(KVM_ARCH_FLAG_SYSTEM_SUSPEND_ENABLED, &kvm->arch.flags);
>>  		break;
>> +	case KVM_CAP_ARM_RME:
>> +		if (!static_branch_unlikely(&kvm_rme_is_available))
>> +			return -EINVAL;
>> +		mutex_lock(&kvm->lock);
>> +		r = kvm_realm_enable_cap(kvm, cap);
>> +		mutex_unlock(&kvm->lock);
>> +		break;
>>  	default:
>>  		r = -EINVAL;
>>  		break;
>> @@ -172,6 +179,13 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>>  	 */
>>  	kvm->arch.dfr0_pmuver.imp = kvm_arm_pmu_get_pmuver_limit();
>>  
>> +	/* Initialise the realm bits after the generic bits are enabled */
>> +	if (kvm_is_realm(kvm)) {
>> +		ret = kvm_init_realm_vm(kvm);
>> +		if (ret)
>> +			goto err_free_cpumask;
>> +	}
>> +
>>  	return 0;
>>  
>>  err_free_cpumask:
>> @@ -204,6 +218,8 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
>>  	kvm_destroy_vcpus(kvm);
>>  
>>  	kvm_unshare_hyp(kvm, kvm + 1);
>> +
>> +	kvm_destroy_realm(kvm);
>>  }
>>  
>>  int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>> @@ -300,6 +316,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>>  	case KVM_CAP_ARM_PTRAUTH_GENERIC:
>>  		r = system_has_full_ptr_auth();
>>  		break;
>> +	case KVM_CAP_ARM_RME:
>> +		r = static_key_enabled(&kvm_rme_is_available);
>> +		break;
>>  	default:
>>  		r = 0;
>>  	}
>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
>> index 31d7fa4c7c14..d0f707767d05 100644
>> --- a/arch/arm64/kvm/mmu.c
>> +++ b/arch/arm64/kvm/mmu.c
>> @@ -840,6 +840,12 @@ void kvm_free_stage2_pgd(struct kvm_s2_mmu *mmu)
>>  	struct kvm_pgtable *pgt = NULL;
>>  
>>  	write_lock(&kvm->mmu_lock);
>> +	if (kvm_is_realm(kvm) &&
>> +	    kvm_realm_state(kvm) != REALM_STATE_DYING) {
>> +		/* TODO: teardown rtts */
>> +		write_unlock(&kvm->mmu_lock);
>> +		return;
>> +	}
>>  	pgt = mmu->pgt;
>>  	if (pgt) {
>>  		mmu->pgd_phys = 0;
>> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
>> index e0267f672b8a..c165df174737 100644
>> --- a/arch/arm64/kvm/reset.c
>> +++ b/arch/arm64/kvm/reset.c
>> @@ -395,3 +395,36 @@ int kvm_set_ipa_limit(void)
>>  
>>  	return 0;
>>  }
>> +
> 
> The below function doesn't have an user in this patch. Also,
> it looks like a part of copy from kvm_init_stage2_mmu()
> in arch/arm64/kvm/mmu.c.

Good spot ;) Yes I discovered this, it should have been removed - it's
no longer used. I think this was an error when I was rebasing:
kvm_arm_setup-stage2() was removed in 315775ff7c6d ("KVM: arm64:
Consolidate stage-2 initialisation into a single function").

Steve

>> +int kvm_arm_setup_stage2(struct kvm *kvm, unsigned long type)
>> +{
>> +	u64 mmfr0, mmfr1;
>> +	u32 phys_shift;
>> +	u32 ipa_limit = kvm_ipa_limit;
>> +
>> +	if (kvm_is_realm(kvm))
>> +		ipa_limit = kvm_realm_ipa_limit();
>> +
>> +	if (type & ~KVM_VM_TYPE_ARM_IPA_SIZE_MASK)
>> +		return -EINVAL;
>> +
>> +	phys_shift = KVM_VM_TYPE_ARM_IPA_SIZE(type);
>> +	if (phys_shift) {
>> +		if (phys_shift > ipa_limit ||
>> +		    phys_shift < ARM64_MIN_PARANGE_BITS)
>> +			return -EINVAL;
>> +	} else {
>> +		phys_shift = KVM_PHYS_SHIFT;
>> +		if (phys_shift > ipa_limit) {
>> +			pr_warn_once("%s using unsupported default IPA limit, upgrade your VMM\n",
>> +				     current->comm);
>> +			return -EINVAL;
>> +		}
>> +	}
>> +
>> +	mmfr0 = read_sanitised_ftr_reg(SYS_ID_AA64MMFR0_EL1);
>> +	mmfr1 = read_sanitised_ftr_reg(SYS_ID_AA64MMFR1_EL1);
>> +	kvm->arch.vtcr = kvm_get_vtcr(mmfr0, mmfr1, phys_shift);
>> +
>> +	return 0;
>> +}
>> diff --git a/arch/arm64/kvm/rme.c b/arch/arm64/kvm/rme.c
>> index f6b587bc116e..9f8c5a91b8fc 100644
>> --- a/arch/arm64/kvm/rme.c
>> +++ b/arch/arm64/kvm/rme.c
>> @@ -5,9 +5,49 @@
>>  
>>  #include <linux/kvm_host.h>
>>  
>> +#include <asm/kvm_emulate.h>
>> +#include <asm/kvm_mmu.h>
>>  #include <asm/rmi_cmds.h>
>>  #include <asm/virt.h>
>>  
>> +/************ FIXME: Copied from kvm/hyp/pgtable.c **********/
>> +#include <asm/kvm_pgtable.h>
>> +
>> +struct kvm_pgtable_walk_data {
>> +	struct kvm_pgtable		*pgt;
>> +	struct kvm_pgtable_walker	*walker;
>> +
>> +	u64				addr;
>> +	u64				end;
>> +};
>> +
>> +static u32 __kvm_pgd_page_idx(struct kvm_pgtable *pgt, u64 addr)
>> +{
>> +	u64 shift = kvm_granule_shift(pgt->start_level - 1); /* May underflow */
>> +	u64 mask = BIT(pgt->ia_bits) - 1;
>> +
>> +	return (addr & mask) >> shift;
>> +}
>> +
>> +static u32 kvm_pgd_pages(u32 ia_bits, u32 start_level)
>> +{
>> +	struct kvm_pgtable pgt = {
>> +		.ia_bits	= ia_bits,
>> +		.start_level	= start_level,
>> +	};
>> +
>> +	return __kvm_pgd_page_idx(&pgt, -1ULL) + 1;
>> +}
>> +
>> +/******************/
>> +
>> +static unsigned long rmm_feat_reg0;
>> +
>> +static bool rme_supports(unsigned long feature)
>> +{
>> +	return !!u64_get_bits(rmm_feat_reg0, feature);
>> +}
>> +
>>  static int rmi_check_version(void)
>>  {
>>  	struct arm_smccc_res res;
>> @@ -33,8 +73,319 @@ static int rmi_check_version(void)
>>  	return 0;
>>  }
>>  
>> +static unsigned long create_realm_feat_reg0(struct kvm *kvm)
>> +{
>> +	unsigned long ia_bits = VTCR_EL2_IPA(kvm->arch.vtcr);
>> +	u64 feat_reg0 = 0;
>> +
>> +	int num_bps = u64_get_bits(rmm_feat_reg0,
>> +				   RMI_FEATURE_REGISTER_0_NUM_BPS);
>> +	int num_wps = u64_get_bits(rmm_feat_reg0,
>> +				   RMI_FEATURE_REGISTER_0_NUM_WPS);
>> +
>> +	feat_reg0 |= u64_encode_bits(ia_bits, RMI_FEATURE_REGISTER_0_S2SZ);
>> +	feat_reg0 |= u64_encode_bits(num_bps, RMI_FEATURE_REGISTER_0_NUM_BPS);
>> +	feat_reg0 |= u64_encode_bits(num_wps, RMI_FEATURE_REGISTER_0_NUM_WPS);
>> +
>> +	return feat_reg0;
>> +}
>> +
>> +u32 kvm_realm_ipa_limit(void)
>> +{
>> +	return u64_get_bits(rmm_feat_reg0, RMI_FEATURE_REGISTER_0_S2SZ);
>> +}
>> +
>> +static u32 get_start_level(struct kvm *kvm)
>> +{
>> +	long sl0 = FIELD_GET(VTCR_EL2_SL0_MASK, kvm->arch.vtcr);
>> +
>> +	return VTCR_EL2_TGRAN_SL0_BASE - sl0;
>> +}
>> +
>> +static int realm_create_rd(struct kvm *kvm)
>> +{
>> +	struct realm *realm = &kvm->arch.realm;
>> +	struct realm_params *params = realm->params;
>> +	void *rd = NULL;
>> +	phys_addr_t rd_phys, params_phys;
>> +	struct kvm_pgtable *pgt = kvm->arch.mmu.pgt;
>> +	unsigned int pgd_sz;
>> +	int i, r;
>> +
>> +	if (WARN_ON(realm->rd) || WARN_ON(!realm->params))
>> +		return -EEXIST;
>> +
>> +	rd = (void *)__get_free_page(GFP_KERNEL);
>> +	if (!rd)
>> +		return -ENOMEM;
>> +
>> +	rd_phys = virt_to_phys(rd);
>> +	if (rmi_granule_delegate(rd_phys)) {
>> +		r = -ENXIO;
>> +		goto out;
>> +	}
>> +
>> +	pgd_sz = kvm_pgd_pages(pgt->ia_bits, pgt->start_level);
>> +	for (i = 0; i < pgd_sz; i++) {
>> +		phys_addr_t pgd_phys = kvm->arch.mmu.pgd_phys + i * PAGE_SIZE;
>> +
>> +		if (rmi_granule_delegate(pgd_phys)) {
>> +			r = -ENXIO;
>> +			goto out_undelegate_tables;
>> +		}
>> +	}
>> +
>> +	params->rtt_level_start = get_start_level(kvm);
>> +	params->rtt_num_start = pgd_sz;
>> +	params->rtt_base = kvm->arch.mmu.pgd_phys;
>> +	params->vmid = realm->vmid;
>> +
>> +	params_phys = virt_to_phys(params);
>> +
>> +	if (rmi_realm_create(rd_phys, params_phys)) {
>> +		r = -ENXIO;
>> +		goto out_undelegate_tables;
>> +	}
>> +
>> +	realm->rd = rd;
>> +	realm->ia_bits = VTCR_EL2_IPA(kvm->arch.vtcr);
>> +
>> +	if (WARN_ON(rmi_rec_aux_count(rd_phys, &realm->num_aux))) {
>> +		WARN_ON(rmi_realm_destroy(rd_phys));
>> +		goto out_undelegate_tables;
>> +	}
>> +
>> +	return 0;
>> +
>> +out_undelegate_tables:
>> +	while (--i >= 0) {
>> +		phys_addr_t pgd_phys = kvm->arch.mmu.pgd_phys + i * PAGE_SIZE;
>> +
>> +		WARN_ON(rmi_granule_undelegate(pgd_phys));
>> +	}
>> +	WARN_ON(rmi_granule_undelegate(rd_phys));
>> +out:
>> +	free_page((unsigned long)rd);
>> +	return r;
>> +}
>> +
>> +/* Protects access to rme_vmid_bitmap */
>> +static DEFINE_SPINLOCK(rme_vmid_lock);
>> +static unsigned long *rme_vmid_bitmap;
>> +
>> +static int rme_vmid_init(void)
>> +{
>> +	unsigned int vmid_count = 1 << kvm_get_vmid_bits();
>> +
>> +	rme_vmid_bitmap = bitmap_zalloc(vmid_count, GFP_KERNEL);
>> +	if (!rme_vmid_bitmap) {
>> +		kvm_err("%s: Couldn't allocate rme vmid bitmap\n", __func__);
>> +		return -ENOMEM;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +static int rme_vmid_reserve(void)
>> +{
>> +	int ret;
>> +	unsigned int vmid_count = 1 << kvm_get_vmid_bits();
>> +
>> +	spin_lock(&rme_vmid_lock);
>> +	ret = bitmap_find_free_region(rme_vmid_bitmap, vmid_count, 0);
>> +	spin_unlock(&rme_vmid_lock);
>> +
>> +	return ret;
>> +}
>> +
>> +static void rme_vmid_release(unsigned int vmid)
>> +{
>> +	spin_lock(&rme_vmid_lock);
>> +	bitmap_release_region(rme_vmid_bitmap, vmid, 0);
>> +	spin_unlock(&rme_vmid_lock);
>> +}
>> +
>> +static int kvm_create_realm(struct kvm *kvm)
>> +{
>> +	struct realm *realm = &kvm->arch.realm;
>> +	int ret;
>> +
>> +	if (!kvm_is_realm(kvm) || kvm_realm_state(kvm) != REALM_STATE_NONE)
>> +		return -EEXIST;
>> +
>> +	ret = rme_vmid_reserve();
>> +	if (ret < 0)
>> +		return ret;
>> +	realm->vmid = ret;
>> +
>> +	ret = realm_create_rd(kvm);
>> +	if (ret) {
>> +		rme_vmid_release(realm->vmid);
>> +		return ret;
>> +	}
>> +
>> +	WRITE_ONCE(realm->state, REALM_STATE_NEW);
>> +
>> +	/* The realm is up, free the parameters.  */
>> +	free_page((unsigned long)realm->params);
>> +	realm->params = NULL;
>> +
>> +	return 0;
>> +}
>> +
>> +static int config_realm_hash_algo(struct realm *realm,
>> +				  struct kvm_cap_arm_rme_config_item *cfg)
>> +{
>> +	switch (cfg->hash_algo) {
>> +	case KVM_CAP_ARM_RME_MEASUREMENT_ALGO_SHA256:
>> +		if (!rme_supports(RMI_FEATURE_REGISTER_0_HASH_SHA_256))
>> +			return -EINVAL;
>> +		break;
>> +	case KVM_CAP_ARM_RME_MEASUREMENT_ALGO_SHA512:
>> +		if (!rme_supports(RMI_FEATURE_REGISTER_0_HASH_SHA_512))
>> +			return -EINVAL;
>> +		break;
>> +	default:
>> +		return -EINVAL;
>> +	}
>> +	realm->params->measurement_algo = cfg->hash_algo;
>> +	return 0;
>> +}
>> +
>> +static int config_realm_sve(struct realm *realm,
>> +			    struct kvm_cap_arm_rme_config_item *cfg)
>> +{
>> +	u64 features_0 = realm->params->features_0;
>> +	int max_sve_vq = u64_get_bits(rmm_feat_reg0,
>> +				      RMI_FEATURE_REGISTER_0_SVE_VL);
>> +
>> +	if (!rme_supports(RMI_FEATURE_REGISTER_0_SVE_EN))
>> +		return -EINVAL;
>> +
>> +	if (cfg->sve_vq > max_sve_vq)
>> +		return -EINVAL;
>> +
>> +	features_0 &= ~(RMI_FEATURE_REGISTER_0_SVE_EN |
>> +			RMI_FEATURE_REGISTER_0_SVE_VL);
>> +	features_0 |= u64_encode_bits(1, RMI_FEATURE_REGISTER_0_SVE_EN);
>> +	features_0 |= u64_encode_bits(cfg->sve_vq,
>> +				      RMI_FEATURE_REGISTER_0_SVE_VL);
>> +
>> +	realm->params->features_0 = features_0;
>> +	return 0;
>> +}
>> +
>> +static int kvm_rme_config_realm(struct kvm *kvm, struct kvm_enable_cap *cap)
>> +{
>> +	struct kvm_cap_arm_rme_config_item cfg;
>> +	struct realm *realm = &kvm->arch.realm;
>> +	int r = 0;
>> +
>> +	if (kvm_realm_state(kvm) != REALM_STATE_NONE)
>> +		return -EBUSY;
>> +
>> +	if (copy_from_user(&cfg, (void __user *)cap->args[1], sizeof(cfg)))
>> +		return -EFAULT;
>> +
>> +	switch (cfg.cfg) {
>> +	case KVM_CAP_ARM_RME_CFG_RPV:
>> +		memcpy(&realm->params->rpv, &cfg.rpv, sizeof(cfg.rpv));
>> +		break;
>> +	case KVM_CAP_ARM_RME_CFG_HASH_ALGO:
>> +		r = config_realm_hash_algo(realm, &cfg);
>> +		break;
>> +	case KVM_CAP_ARM_RME_CFG_SVE:
>> +		r = config_realm_sve(realm, &cfg);
>> +		break;
>> +	default:
>> +		r = -EINVAL;
>> +	}
>> +
>> +	return r;
>> +}
>> +
>> +int kvm_realm_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
>> +{
>> +	int r = 0;
>> +
>> +	switch (cap->args[0]) {
>> +	case KVM_CAP_ARM_RME_CONFIG_REALM:
>> +		r = kvm_rme_config_realm(kvm, cap);
>> +		break;
>> +	case KVM_CAP_ARM_RME_CREATE_RD:
>> +		if (kvm->created_vcpus) {
>> +			r = -EBUSY;
>> +			break;
>> +		}
>> +
>> +		r = kvm_create_realm(kvm);
>> +		break;
>> +	default:
>> +		r = -EINVAL;
>> +		break;
>> +	}
>> +
>> +	return r;
>> +}
>> +
>> +void kvm_destroy_realm(struct kvm *kvm)
>> +{
>> +	struct realm *realm = &kvm->arch.realm;
>> +	struct kvm_pgtable *pgt = kvm->arch.mmu.pgt;
>> +	unsigned int pgd_sz;
>> +	int i;
>> +
>> +	if (realm->params) {
>> +		free_page((unsigned long)realm->params);
>> +		realm->params = NULL;
>> +	}
>> +
>> +	if (kvm_realm_state(kvm) == REALM_STATE_NONE)
>> +		return;
>> +
>> +	WRITE_ONCE(realm->state, REALM_STATE_DYING);
>> +
>> +	rme_vmid_release(realm->vmid);
>> +
>> +	if (realm->rd) {
>> +		phys_addr_t rd_phys = virt_to_phys(realm->rd);
>> +
>> +		if (WARN_ON(rmi_realm_destroy(rd_phys)))
>> +			return;
>> +		if (WARN_ON(rmi_granule_undelegate(rd_phys)))
>> +			return;
>> +		free_page((unsigned long)realm->rd);
>> +		realm->rd = NULL;
>> +	}
>> +
>> +	pgd_sz = kvm_pgd_pages(pgt->ia_bits, pgt->start_level);
>> +	for (i = 0; i < pgd_sz; i++) {
>> +		phys_addr_t pgd_phys = kvm->arch.mmu.pgd_phys + i * PAGE_SIZE;
>> +
>> +		if (WARN_ON(rmi_granule_undelegate(pgd_phys)))
>> +			return;
>> +	}
>> +
>> +	kvm_free_stage2_pgd(&kvm->arch.mmu);
>> +}
>> +
>> +int kvm_init_realm_vm(struct kvm *kvm)
>> +{
>> +	struct realm_params *params;
>> +
>> +	params = (struct realm_params *)get_zeroed_page(GFP_KERNEL);
>> +	if (!params)
>> +		return -ENOMEM;
>> +
>> +	params->features_0 = create_realm_feat_reg0(kvm);
>> +	kvm->arch.realm.params = params;
>> +	return 0;
>> +}
>> +
>>  int kvm_init_rme(void)
>>  {
>> +	int ret;
>> +
>>  	if (PAGE_SIZE != SZ_4K)
>>  		/* Only 4k page size on the host is supported */
>>  		return 0;
>> @@ -43,6 +394,12 @@ int kvm_init_rme(void)
>>  		/* Continue without realm support */
>>  		return 0;
>>  
>> +	ret = rme_vmid_init();
>> +	if (ret)
>> +		return ret;
>> +
>> +	WARN_ON(rmi_features(0, &rmm_feat_reg0));
>> +
>>  	/* Future patch will enable static branch kvm_rme_is_available */
>>  
>>  	return 0;
>