Re: [PATCH v6 12/43] arm64: RME: Allocate/free RECs to match vCPUs

[Gavin Shan <gshan@redhat.com>]

On 12/13/24 1:55 AM, 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 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                 |   9 ++
>   arch/arm64/kvm/reset.c               |  11 ++
>   arch/arm64/kvm/rme.c                 | 144 +++++++++++++++++++++++++++
>   6 files changed, 192 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index 27f54a7778aa..ec2b6d9c9c07 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -722,7 +722,14 @@ 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;
>   }
>   

It seems the check on kvm_rme_is_available is unnecessary because KVM_ARM_VCPU_REC
is possible to be true only when kvm_rme_is_available is true.

> +static inline bool kvm_arm_vcpu_rec_finalized(struct kvm_vcpu *vcpu)
> +{
> +	return vcpu->arch.rec.mpidr != INVALID_HWID;
> +}
> +
>   #endif /* __ARM64_KVM_EMULATE_H__ */

I would suggest to rename to kvm_arm_rec_finalized() since vCPU and REC are
similar objects at the same level. It'd better to avoid duplicate object
name reference in the function name.

> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 8482638dce3b..220195c727ef 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -789,6 +789,9 @@ 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 32bdedf1d866..62d4a63d3035 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);
>   
>   #define RMM_RTT_BLOCK_LEVEL	2
>   #define RMM_RTT_MAX_LEVEL	3
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 73016e1e0067..2d97147651be 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -525,6 +525,8 @@ 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 */
> @@ -1467,6 +1469,9 @@ 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 (!static_branch_unlikely(&kvm_rme_is_available))
> +		clear_bit(KVM_ARM_VCPU_REC, &features);
> +
>   	return features;
>   }
>   
> @@ -1506,6 +1511,10 @@ 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;
>   }
>   

One corner case seems missed in kvm_vcpu_init_check_features(). It's allowed to
initialize a vCPU with REC feature even kvm_is_realm(kvm) is false. Hopefully,
I didn't miss something.

[...]

Thanks,
Gavin