Re: [PATCH v7 12/45] arm64: RME: Allocate/free RECs to match vCPUs

Wei-Lin Chang
2025-04-07T15:04:43Z

Hi Steven,

On Thu, Feb 13, 2025 at 04:13:52PM +0000, 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@arm.com>
> ---
> 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 | 18 +++
> arch/arm64/kvm/arm.c | 13 +-
> arch/arm64/kvm/reset.c | 11 ++
> arch/arm64/kvm/rme.c | 179 +++++++++++++++++++++++++++
> 6 files changed, 229 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index 909c5c3b7632..f7b5a78f2e91 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -711,7 +711,14 @@ 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 992eb2a6f56f..016d0685958d 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -803,6 +803,9 @@ 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 698bb48a8ae1..5db377943db4 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 +66,21 @@ 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;
> + 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 +88,8 @@ 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 917ee7c674f5..a6a3034a2f50 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -496,6 +496,8 @@ 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 */
> @@ -1433,7 +1435,7 @@ 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;
>
> @@ -1454,6 +1456,9 @@ 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;
> }
>
> @@ -1471,7 +1476,7 @@ 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;
>
> /*
> @@ -1493,6 +1498,10 @@ 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 803e11b0dc8f..a6423ef20144 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 f5d79efee454..0aa1f29b0610 100644
> --- a/arch/arm64/kvm/rme.c
> +++ b/arch/arm64/kvm/rme.c
> @@ -474,6 +474,185 @@ 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);
> + bool undelegate_failed = false;
> +
> + for (j = 0; j < PAGE_SIZE && i < num_aux; j += RMM_PAGE_SIZE) {
> + if (WARN_ON(rmi_granule_undelegate(aux_page_phys)))
> + undelegate_failed = true;
> + aux_page_phys += RMM_PAGE_SIZE;
> + i++;
> + }
> + if (!undelegate_failed)
> + __free_page(aux_page);
> + }
> +}
> +

Just a small stylistic comment:
I feel it can be slightly clearer if the double negative

bool undelegate_failed = false;

can be just:
bool undelegate_succeeded = true;

with the other true/false flipped, the if condition also won't need to be
negated.

Thanks,
Wei-Lin Chang

> +static int alloc_rec_aux(struct page **aux_pages,
> + u64 *aux_phys_pages,
> + 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;
> +
> + 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);
> +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)
> {
> struct realm_params *params;
> --
> 2.43.0
>