Message-ID: <3a230094-18ab-417a-8eba-adc86a6b2f00@arm.com>
Date: Thu, 1 May 2025 17:50:32 +0100
From: Suzuki K Poulose <suzuki.poulose@....com>
To: Steven Price <steven.price@....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>, 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>,
 Gavin Shan <gshan@...hat.com>, Shanker Donthineni <sdonthineni@...dia.com>,
 Alper Gun <alpergun@...gle.com>, "Aneesh Kumar K . V"
 <aneesh.kumar@...nel.org>
Subject: Re: [PATCH v8 11/43] arm64: RME: Allocate/free RECs to match vCPUs

On 16/04/2025 14:41, Steven Price wrote:
> The RMM maintains a data structure known as the Realm Execution Context
> (or REC). It is similar to struct kvm_vcpu and tracks the state of the
> virtual CPUs. KVM must delegate memory and request the structures are
> created when vCPUs are created, and suitably tear down on destruction.
> 
> RECs must also be supplied with addition pages - auxiliary (or AUX)
> granules - for storing the larger registers state (e.g. for SVE). The
> number of AUX granules for a REC depends on the parameters with which
> the Realm was created - the RMM makes this information available via the
> RMI_REC_AUX_COUNT call performed after creating the Realm Descriptor (RD).
> 
> Note that only some of register state for the REC can be set by KVM, the
> rest is defined by the RMM (zeroed). The register state then cannot be
> changed by KVM after the REC is created (except when the guest
> explicitly requests this e.g. by performing a PSCI call). The RMM also
> requires that the VMM creates RECs in ascending order of the MPIDR.
> 
> See Realm Management Monitor specification (DEN0137) for more information:
> https://developer.arm.com/documentation/den0137/
> 
> Signed-off-by: Steven Price <steven.price@....com>
> Reviewed-by: Gavin Shan <gshan@...hat.com>

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


> ---
> Changes since v7:
>   * Add comment explaining the aux_pages array.
>   * Rename "undeleted_failed" variable to "should_free" to avoid a
>     confusing double negative.
> Changes since v6:
>   * Avoid reporting the KVM_ARM_VCPU_REC feature if the guest isn't a
>     realm guest.
>   * Support host page size being larger than RMM's granule size when
>     allocating/freeing aux granules.
> Changes since v5:
>   * Separate the concept of vcpu_is_rec() and
>     kvm_arm_vcpu_rec_finalized() by using the KVM_ARM_VCPU_REC feature as
>     the indication that the VCPU is a REC.
> Changes since v2:
>   * Free rec->run earlier in kvm_destroy_realm() and adapt to previous patches.
> ---
>   arch/arm64/include/asm/kvm_emulate.h |   7 ++
>   arch/arm64/include/asm/kvm_host.h    |   3 +
>   arch/arm64/include/asm/kvm_rme.h     |  27 ++++
>   arch/arm64/kvm/arm.c                 |  13 +-
>   arch/arm64/kvm/reset.c               |  11 ++
>   arch/arm64/kvm/rme.c                 | 180 +++++++++++++++++++++++++++
>   6 files changed, 239 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index 4ee6c215da82..c803c8188d9c 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -706,7 +706,14 @@ static inline bool kvm_realm_is_created(struct kvm *kvm)
>   
>   static inline bool vcpu_is_rec(struct kvm_vcpu *vcpu)
>   {
> +	if (static_branch_unlikely(&kvm_rme_is_available))
> +		return vcpu_has_feature(vcpu, KVM_ARM_VCPU_REC);
>   	return false;
>   }
>   
> +static inline bool kvm_arm_rec_finalized(struct kvm_vcpu *vcpu)
> +{
> +	return vcpu->arch.rec.mpidr != INVALID_HWID;
> +}
> +
>   #endif /* __ARM64_KVM_EMULATE_H__ */
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 7bd81b86eab0..ceb5e60ae5ae 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -828,6 +828,9 @@ struct kvm_vcpu_arch {
>   
>   	/* Per-vcpu CCSIDR override or NULL */
>   	u32 *ccsidr;
> +
> +	/* Realm meta data */
> +	struct realm_rec rec;
>   };
>   
>   /*
> diff --git a/arch/arm64/include/asm/kvm_rme.h b/arch/arm64/include/asm/kvm_rme.h
> index 5f0de9a6d339..f716b890e484 100644
> --- a/arch/arm64/include/asm/kvm_rme.h
> +++ b/arch/arm64/include/asm/kvm_rme.h
> @@ -6,6 +6,7 @@
>   #ifndef __ASM_KVM_RME_H
>   #define __ASM_KVM_RME_H
>   
> +#include <asm/rmi_smc.h>
>   #include <uapi/linux/kvm.h>
>   
>   /**
> @@ -65,6 +66,30 @@ struct realm {
>   	unsigned int ia_bits;
>   };
>   
> +/**
> + * struct realm_rec - Additional per VCPU data for a Realm
> + *
> + * @mpidr: MPIDR (Multiprocessor Affinity Register) value to identify this VCPU
> + * @rec_page: Kernel VA of the RMM's private page for this REC
> + * @aux_pages: Additional pages private to the RMM for this REC
> + * @run: Kernel VA of the RmiRecRun structure shared with the RMM
> + */
> +struct realm_rec {
> +	unsigned long mpidr;
> +	void *rec_page;
> +	/*
> +	 * REC_PARAMS_AUX_GRANULES is the maximum number of granules that the
> +	 * RMM can require. By using that to size the array we know that it
> +	 * will be big enough as the page size is always at least as large as
> +	 * the granule size. In the case of a larger page size than 4k (or an
> +	 * RMM which requires fewer auxiliary granules), the array will be
> +	 * bigger than needed however the extra memory required is small and
> +	 * this keeps the code cleaner.
> +	 */
> +	struct page *aux_pages[REC_PARAMS_AUX_GRANULES];
> +	struct rec_run *run;
> +};
> +
>   void kvm_init_rme(void);
>   u32 kvm_realm_ipa_limit(void);
>   
> @@ -72,6 +97,8 @@ 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);
>   void kvm_realm_destroy_rtts(struct kvm *kvm, u32 ia_bits);
> +int kvm_create_rec(struct kvm_vcpu *vcpu);
> +void kvm_destroy_rec(struct kvm_vcpu *vcpu);
>   
>   static inline bool kvm_realm_is_private_address(struct realm *realm,
>   						unsigned long addr)
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index ba55950e6a6e..fd83efb667cc 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -489,6 +489,8 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
>   	/* Force users to call KVM_ARM_VCPU_INIT */
>   	vcpu_clear_flag(vcpu, VCPU_INITIALIZED);
>   
> +	vcpu->arch.rec.mpidr = INVALID_HWID;
> +
>   	vcpu->arch.mmu_page_cache.gfp_zero = __GFP_ZERO;
>   
>   	/* Set up the timer */
> @@ -1447,7 +1449,7 @@ int kvm_vm_ioctl_irq_line(struct kvm *kvm, struct kvm_irq_level *irq_level,
>   	return -EINVAL;
>   }
>   
> -static unsigned long system_supported_vcpu_features(void)
> +static unsigned long system_supported_vcpu_features(struct kvm *kvm)
>   {
>   	unsigned long features = KVM_VCPU_VALID_FEATURES;
>   
> @@ -1468,6 +1470,9 @@ static unsigned long system_supported_vcpu_features(void)
>   	if (!cpus_have_final_cap(ARM64_HAS_NESTED_VIRT))
>   		clear_bit(KVM_ARM_VCPU_HAS_EL2, &features);
>   
> +	if (!kvm_is_realm(kvm))
> +		clear_bit(KVM_ARM_VCPU_REC, &features);
> +
>   	return features;
>   }
>   
> @@ -1485,7 +1490,7 @@ static int kvm_vcpu_init_check_features(struct kvm_vcpu *vcpu,
>   			return -ENOENT;
>   	}
>   
> -	if (features & ~system_supported_vcpu_features())
> +	if (features & ~system_supported_vcpu_features(vcpu->kvm))
>   		return -EINVAL;
>   
>   	/*
> @@ -1507,6 +1512,10 @@ static int kvm_vcpu_init_check_features(struct kvm_vcpu *vcpu,
>   	if (test_bit(KVM_ARM_VCPU_HAS_EL2, &features))
>   		return -EINVAL;
>   
> +	/* RME is incompatible with AArch32 */
> +	if (test_bit(KVM_ARM_VCPU_REC, &features))
> +		return -EINVAL;
> +
>   	return 0;
>   }
>   
> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> index f82fcc614e13..7ba3c7918a0b 100644
> --- a/arch/arm64/kvm/reset.c
> +++ b/arch/arm64/kvm/reset.c
> @@ -137,6 +137,11 @@ int kvm_arm_vcpu_finalize(struct kvm_vcpu *vcpu, int feature)
>   			return -EPERM;
>   
>   		return kvm_vcpu_finalize_sve(vcpu);
> +	case KVM_ARM_VCPU_REC:
> +		if (!kvm_is_realm(vcpu->kvm) || !vcpu_is_rec(vcpu))
> +			return -EINVAL;
> +
> +		return kvm_create_rec(vcpu);
>   	}
>   
>   	return -EINVAL;
> @@ -147,6 +152,11 @@ bool kvm_arm_vcpu_is_finalized(struct kvm_vcpu *vcpu)
>   	if (vcpu_has_sve(vcpu) && !kvm_arm_vcpu_sve_finalized(vcpu))
>   		return false;
>   
> +	if (kvm_is_realm(vcpu->kvm) &&
> +	    !(vcpu_is_rec(vcpu) && kvm_arm_rec_finalized(vcpu) &&
> +	      READ_ONCE(vcpu->kvm->arch.realm.state) == REALM_STATE_ACTIVE))
> +		return false;
> +
>   	return true;
>   }
>   
> @@ -159,6 +169,7 @@ void kvm_arm_vcpu_destroy(struct kvm_vcpu *vcpu)
>   		kvm_unshare_hyp(sve_state, sve_state + vcpu_sve_state_size(vcpu));
>   	kfree(sve_state);
>   	kfree(vcpu->arch.ccsidr);
> +	kvm_destroy_rec(vcpu);
>   }
>   
>   static void kvm_vcpu_reset_sve(struct kvm_vcpu *vcpu)
> diff --git a/arch/arm64/kvm/rme.c b/arch/arm64/kvm/rme.c
> index 3053261c3b52..f4923fc3b34e 100644
> --- a/arch/arm64/kvm/rme.c
> +++ b/arch/arm64/kvm/rme.c
> @@ -474,6 +474,186 @@ void kvm_destroy_realm(struct kvm *kvm)
>   	kvm_free_stage2_pgd(&kvm->arch.mmu);
>   }
>   
> +static void free_rec_aux(struct page **aux_pages,
> +			 unsigned int num_aux)
> +{
> +	unsigned int i, j;
> +	unsigned int page_count = 0;
> +
> +	for (i = 0; i < num_aux;) {
> +		struct page *aux_page = aux_pages[page_count++];
> +		phys_addr_t aux_page_phys = page_to_phys(aux_page);

[ Coming back to the top after a full review, feel free to ignore
the comments on the naming with non-4K support code. ]

minor nit: aux_phys_granule ? or even aux_granule ? "page" is confusing.

> +		bool should_free = true;
> +
> +		for (j = 0; j < PAGE_SIZE && i < num_aux; j += RMM_PAGE_SIZE) {
> +			if (WARN_ON(rmi_granule_undelegate(aux_page_phys)))
> +				should_free = false;
> +			aux_page_phys += RMM_PAGE_SIZE;
> +			i++;
> +		}
> +		/* Only free if all the undelegate calls were successful */
> +		if (should_free)
> +			__free_page(aux_page);
> +	}
> +}
> +
> +static int alloc_rec_aux(struct page **aux_pages,
> +			 u64 *aux_phys_pages,

minor nit: aux_[phys_]?granules ? as we are storing the granules here.

> +			 unsigned int num_aux)
> +{
> +	struct page *aux_page;
> +	int page_count = 0;
> +	unsigned int i, j;
> +	int ret;
> +
> +	for (i = 0; i < num_aux;) {
> +		phys_addr_t aux_page_phys;

same here, aux_granule

> +
> +		aux_page = alloc_page(GFP_KERNEL);
> +		if (!aux_page) {
> +			ret = -ENOMEM;
> +			goto out_err;
> +		}
> +
> +		aux_page_phys = page_to_phys(aux_page);
> +		for (j = 0; j < PAGE_SIZE && i < num_aux; j += RMM_PAGE_SIZE) {
> +			if (rmi_granule_delegate(aux_page_phys)) {
> +				ret = -ENXIO;
> +				goto err_undelegate;
> +			}
> +			aux_phys_pages[i++] = aux_page_phys;
> +			aux_page_phys += RMM_PAGE_SIZE;
> +		}
> +		aux_pages[page_count++] = aux_page;
> +	}
> +
> +	return 0;
> +err_undelegate:
> +	while (j > 0) {
> +		j -= RMM_PAGE_SIZE;
> +		i--;
> +		if (WARN_ON(rmi_granule_undelegate(aux_phys_pages[i]))) {
> +			/* Leak the page if the undelegate fails */
> +			goto out_err;
> +		}
> +	}
> +	__free_page(aux_page);
> +out_err:
> +	free_rec_aux(aux_pages, i);
> +	return ret;
> +}
> +
> +int kvm_create_rec(struct kvm_vcpu *vcpu)
> +{
> +	struct user_pt_regs *vcpu_regs = vcpu_gp_regs(vcpu);
> +	unsigned long mpidr = kvm_vcpu_get_mpidr_aff(vcpu);
> +	struct realm *realm = &vcpu->kvm->arch.realm;
> +	struct realm_rec *rec = &vcpu->arch.rec;
> +	unsigned long rec_page_phys;
> +	struct rec_params *params;
> +	int r, i;
> +
> +	if (kvm_realm_state(vcpu->kvm) != REALM_STATE_NEW)
> +		return -ENOENT;
> +
> +	if (rec->run)
> +		return -EBUSY;
> +
> +	/*
> +	 * The RMM will report PSCI v1.0 to Realms and the KVM_ARM_VCPU_PSCI_0_2
> +	 * flag covers v0.2 and onwards.
> +	 */
> +	if (!vcpu_has_feature(vcpu, KVM_ARM_VCPU_PSCI_0_2))
> +		return -EINVAL;
> +
> +	BUILD_BUG_ON(sizeof(*params) > PAGE_SIZE);
> +	BUILD_BUG_ON(sizeof(*rec->run) > PAGE_SIZE);
> +
> +	params = (struct rec_params *)get_zeroed_page(GFP_KERNEL);
> +	rec->rec_page = (void *)__get_free_page(GFP_KERNEL);
> +	rec->run = (void *)get_zeroed_page(GFP_KERNEL);
> +	if (!params || !rec->rec_page || !rec->run) {
> +		r = -ENOMEM;
> +		goto out_free_pages;
> +	}
> +
> +	for (i = 0; i < ARRAY_SIZE(params->gprs); i++)
> +		params->gprs[i] = vcpu_regs->regs[i];
> +
> +	params->pc = vcpu_regs->pc;
> +
> +	if (vcpu->vcpu_id == 0)
> +		params->flags |= REC_PARAMS_FLAG_RUNNABLE;
> +
> +	rec_page_phys = virt_to_phys(rec->rec_page);
> +
> +	if (rmi_granule_delegate(rec_page_phys)) {
> +		r = -ENXIO;
> +		goto out_free_pages;
> +	}
> +
> +	r = alloc_rec_aux(rec->aux_pages, params->aux, realm->num_aux);
> +	if (r)
> +		goto out_undelegate_rmm_rec;
> +
> +	params->num_rec_aux = realm->num_aux;
> +	params->mpidr = mpidr;
> +
> +	if (rmi_rec_create(virt_to_phys(realm->rd),
> +			   rec_page_phys,
> +			   virt_to_phys(params))) {
> +		r = -ENXIO;
> +		goto out_free_rec_aux;
> +	}
> +
> +	rec->mpidr = mpidr;
> +
> +	free_page((unsigned long)params);
> +	return 0;
> +
> +out_free_rec_aux:
> +	free_rec_aux(rec->aux_pages, realm->num_aux);

This is problematic. Realm->num_aux is number of AUX granules, not
num_aux_pages and can easily trigger overflow with non-4K. The 
alloc_rec_aux() is only allocating as many Pages required to cover
the num_aux granules.

I would say, simply drop the non-4K page support change, we can come
back to fixing the non-4K properly later, when we enable it.


Suzuki


> +out_undelegate_rmm_rec:
> +	if (WARN_ON(rmi_granule_undelegate(rec_page_phys)))
> +		rec->rec_page = NULL;
> +out_free_pages:
> +	free_page((unsigned long)rec->run);
> +	free_page((unsigned long)rec->rec_page);
> +	free_page((unsigned long)params);
> +	return r;
> +}
> +
> +void kvm_destroy_rec(struct kvm_vcpu *vcpu)
> +{
> +	struct realm *realm = &vcpu->kvm->arch.realm;
> +	struct realm_rec *rec = &vcpu->arch.rec;
> +	unsigned long rec_page_phys;
> +
> +	if (!vcpu_is_rec(vcpu))
> +		return;
> +
> +	if (!rec->run) {
> +		/* Nothing to do if the VCPU hasn't been finalized */
> +		return;
> +	}
> +
> +	free_page((unsigned long)rec->run);
> +
> +	rec_page_phys = virt_to_phys(rec->rec_page);
> +
> +	/*
> +	 * The REC and any AUX pages cannot be reclaimed until the REC is
> +	 * destroyed. So if the REC destroy fails then the REC page and any AUX
> +	 * pages will be leaked.
> +	 */
> +	if (WARN_ON(rmi_rec_destroy(rec_page_phys)))
> +		return;
> +
> +	free_rec_aux(rec->aux_pages, realm->num_aux);
> +
> +	free_delegated_granule(rec_page_phys);
> +}
> +
>   int kvm_init_realm_vm(struct kvm *kvm)
>   {
>   	kvm->arch.realm.params = (void *)get_zeroed_page(GFP_KERNEL);

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