Re: [PATCH v1 03/11] KVM: arm64: Use guard()/scoped_guard() in arm64 KVM EL1 code

[Vincent Donnefort <vdonnefort@google.com>]

On Fri, Jun 12, 2026 at 07:59:17AM +0100, tabba@google.com wrote:
> Convert the manual mutex_lock()/spin_lock() pairs in
> arch/arm64/kvm/{pkvm,arm,mmu,reset,psci}.c to guard(mutex),
> guard(spinlock) and scoped_guard(), dropping unlock-only goto labels in
> favour of direct returns. Centralised cleanup gotos that still serve
> other resources are preserved.
> 
> reset.c uses scoped_guard() rather than guard() so the lock covers only
> the small read/update window inside kvm_reset_vcpu(), leaving the rest
> of the function outside the critical section.

I believe in that case unless it really helps with cleaning resources, there's
not much point using scoped_guard().

I would keep it as is.

> 
> Signed-off-by: Fuad Tabba <tabba@google.com>
> ---
>  arch/arm64/kvm/arm.c   | 14 +++-----
>  arch/arm64/kvm/mmu.c   | 80 +++++++++++++++---------------------------
>  arch/arm64/kvm/pkvm.c  | 26 ++++++--------
>  arch/arm64/kvm/psci.c  | 17 ++++-----
>  arch/arm64/kvm/reset.c |  8 ++---
>  5 files changed, 53 insertions(+), 92 deletions(-)
> 
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 9453321ef8c6..c9f36932c980 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -793,9 +793,7 @@ int kvm_arch_vcpu_ioctl_get_mpstate(struct kvm_vcpu *vcpu,
>  int kvm_arch_vcpu_ioctl_set_mpstate(struct kvm_vcpu *vcpu,
>  				    struct kvm_mp_state *mp_state)
>  {
> -	int ret = 0;
> -
> -	spin_lock(&vcpu->arch.mp_state_lock);
> +	guard(spinlock)(&vcpu->arch.mp_state_lock);
>  
>  	switch (mp_state->mp_state) {
>  	case KVM_MP_STATE_RUNNABLE:
> @@ -808,12 +806,10 @@ int kvm_arch_vcpu_ioctl_set_mpstate(struct kvm_vcpu *vcpu,
>  		kvm_arm_vcpu_suspend(vcpu);
>  		break;
>  	default:
> -		ret = -EINVAL;
> +		return -EINVAL;
>  	}
>  
> -	spin_unlock(&vcpu->arch.mp_state_lock);
> -
> -	return ret;
> +	return 0;
>  }
>  
>  /**
> @@ -1726,15 +1722,13 @@ static int kvm_arch_vcpu_ioctl_vcpu_init(struct kvm_vcpu *vcpu,
>  	/*
>  	 * Handle the "start in power-off" case.
>  	 */
> -	spin_lock(&vcpu->arch.mp_state_lock);
> +	guard(spinlock)(&vcpu->arch.mp_state_lock);
>  
>  	if (power_off)
>  		__kvm_arm_vcpu_power_off(vcpu);
>  	else
>  		WRITE_ONCE(vcpu->arch.mp_state.mp_state, KVM_MP_STATE_RUNNABLE);
>  
> -	spin_unlock(&vcpu->arch.mp_state_lock);
> -
>  	return 0;
>  }
>  
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 4da9281312eb..d18f4ce7ceae 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -391,13 +391,13 @@ static void stage2_flush_vm(struct kvm *kvm)
>   */
>  void __init free_hyp_pgds(void)
>  {
> -	mutex_lock(&kvm_hyp_pgd_mutex);
> -	if (hyp_pgtable) {
> -		kvm_pgtable_hyp_destroy(hyp_pgtable);
> -		kfree(hyp_pgtable);
> -		hyp_pgtable = NULL;
> -	}
> -	mutex_unlock(&kvm_hyp_pgd_mutex);
> +	guard(mutex)(&kvm_hyp_pgd_mutex);
> +	if (!hyp_pgtable)
> +		return;
> +
> +	kvm_pgtable_hyp_destroy(hyp_pgtable);
> +	kfree(hyp_pgtable);
> +	hyp_pgtable = NULL;
>  }
>  
>  static bool kvm_host_owns_hyp_mappings(void)
> @@ -424,16 +424,11 @@ static bool kvm_host_owns_hyp_mappings(void)
>  int __create_hyp_mappings(unsigned long start, unsigned long size,
>  			  unsigned long phys, enum kvm_pgtable_prot prot)
>  {
> -	int err;
> -
>  	if (WARN_ON(!kvm_host_owns_hyp_mappings()))
>  		return -EINVAL;
>  
> -	mutex_lock(&kvm_hyp_pgd_mutex);
> -	err = kvm_pgtable_hyp_map(hyp_pgtable, start, size, phys, prot);
> -	mutex_unlock(&kvm_hyp_pgd_mutex);
> -
> -	return err;
> +	guard(mutex)(&kvm_hyp_pgd_mutex);
> +	return kvm_pgtable_hyp_map(hyp_pgtable, start, size, phys, prot);
>  }
>  
>  static phys_addr_t kvm_kaddr_to_phys(void *kaddr)
> @@ -481,56 +476,42 @@ static int share_pfn_hyp(u64 pfn)
>  {
>  	struct rb_node **node, *parent;
>  	struct hyp_shared_pfn *this;
> -	int ret = 0;
>  
> -	mutex_lock(&hyp_shared_pfns_lock);
> +	guard(mutex)(&hyp_shared_pfns_lock);
>  	this = find_shared_pfn(pfn, &node, &parent);
>  	if (this) {
>  		this->count++;
> -		goto unlock;
> +		return 0;
>  	}
>  
>  	this = kzalloc_obj(*this);
> -	if (!this) {
> -		ret = -ENOMEM;
> -		goto unlock;
> -	}
> +	if (!this)
> +		return -ENOMEM;
>  
>  	this->pfn = pfn;
>  	this->count = 1;
>  	rb_link_node(&this->node, parent, node);
>  	rb_insert_color(&this->node, &hyp_shared_pfns);
> -	ret = kvm_call_hyp_nvhe(__pkvm_host_share_hyp, pfn);
> -unlock:
> -	mutex_unlock(&hyp_shared_pfns_lock);
> -
> -	return ret;
> +	return kvm_call_hyp_nvhe(__pkvm_host_share_hyp, pfn);
>  }
>  
>  static int unshare_pfn_hyp(u64 pfn)
>  {
>  	struct rb_node **node, *parent;
>  	struct hyp_shared_pfn *this;
> -	int ret = 0;
>  
> -	mutex_lock(&hyp_shared_pfns_lock);
> +	guard(mutex)(&hyp_shared_pfns_lock);
>  	this = find_shared_pfn(pfn, &node, &parent);
> -	if (WARN_ON(!this)) {
> -		ret = -ENOENT;
> -		goto unlock;
> -	}
> +	if (WARN_ON(!this))
> +		return -ENOENT;
>  
>  	this->count--;
>  	if (this->count)
> -		goto unlock;
> +		return 0;
>  
>  	rb_erase(&this->node, &hyp_shared_pfns);
>  	kfree(this);
> -	ret = kvm_call_hyp_nvhe(__pkvm_host_unshare_hyp, pfn);
> -unlock:
> -	mutex_unlock(&hyp_shared_pfns_lock);
> -
> -	return ret;
> +	return kvm_call_hyp_nvhe(__pkvm_host_unshare_hyp, pfn);
>  }
>  
>  int kvm_share_hyp(void *from, void *to)
> @@ -655,7 +636,7 @@ int hyp_alloc_private_va_range(size_t size, unsigned long *haddr)
>  	unsigned long base;
>  	int ret = 0;
>  
> -	mutex_lock(&kvm_hyp_pgd_mutex);
> +	guard(mutex)(&kvm_hyp_pgd_mutex);
>  
>  	/*
>  	 * This assumes that we have enough space below the idmap
> @@ -670,8 +651,6 @@ int hyp_alloc_private_va_range(size_t size, unsigned long *haddr)
>  	base = io_map_base - size;
>  	ret = __hyp_alloc_private_va_range(base);
>  
> -	mutex_unlock(&kvm_hyp_pgd_mutex);
> -
>  	if (!ret)
>  		*haddr = base;
>  
> @@ -714,17 +693,16 @@ int create_hyp_stack(phys_addr_t phys_addr, unsigned long *haddr)
>  	size_t size;
>  	int ret;
>  
> -	mutex_lock(&kvm_hyp_pgd_mutex);
> -	/*
> -	 * Efficient stack verification using the NVHE_STACK_SHIFT bit implies
> -	 * an alignment of our allocation on the order of the size.
> -	 */
> -	size = NVHE_STACK_SIZE * 2;
> -	base = ALIGN_DOWN(io_map_base - size, size);
> +	scoped_guard(mutex, &kvm_hyp_pgd_mutex) {
> +		/*
> +		 * Efficient stack verification using the NVHE_STACK_SHIFT bit implies
> +		 * an alignment of our allocation on the order of the size.
> +		 */
> +		size = NVHE_STACK_SIZE * 2;
> +		base = ALIGN_DOWN(io_map_base - size, size);
>  
> -	ret = __hyp_alloc_private_va_range(base);
> -
> -	mutex_unlock(&kvm_hyp_pgd_mutex);
> +		ret = __hyp_alloc_private_va_range(base);
> +	}

Not sure about that one, it's not shorter, doesn't remove any label but add
a tab.

>  
>  	if (ret) {
>  		kvm_err("Cannot allocate hyp stack guard page\n");
> diff --git a/arch/arm64/kvm/pkvm.c b/arch/arm64/kvm/pkvm.c
> index 053e4f733e4b..a39111b70f9f 100644
> --- a/arch/arm64/kvm/pkvm.c
> +++ b/arch/arm64/kvm/pkvm.c
> @@ -190,39 +190,33 @@ bool pkvm_hyp_vm_is_created(struct kvm *kvm)
>  
>  int pkvm_create_hyp_vm(struct kvm *kvm)
>  {
> -	int ret = 0;
> -
>  	/*
>  	 * Synchronise with kvm_arch_prepare_memory_region(), as we
>  	 * prevent memslot modifications on a pVM that has been run.
>  	 */
> -	mutex_lock(&kvm->slots_lock);
> -	mutex_lock(&kvm->arch.config_lock);
> -	if (!pkvm_hyp_vm_is_created(kvm))
> -		ret = __pkvm_create_hyp_vm(kvm);
> -	mutex_unlock(&kvm->arch.config_lock);
> -	mutex_unlock(&kvm->slots_lock);
> +	guard(mutex)(&kvm->slots_lock);
> +	guard(mutex)(&kvm->arch.config_lock);
>  
> -	return ret;
> +	if (!pkvm_hyp_vm_is_created(kvm))
> +		return __pkvm_create_hyp_vm(kvm);
> +
> +	return 0;
>  }
>  
>  int pkvm_create_hyp_vcpu(struct kvm_vcpu *vcpu)
>  {
> -	int ret = 0;
> +	guard(mutex)(&vcpu->kvm->arch.config_lock);
>  
> -	mutex_lock(&vcpu->kvm->arch.config_lock);
>  	if (!vcpu_get_flag(vcpu, VCPU_PKVM_FINALIZED))
> -		ret = __pkvm_create_hyp_vcpu(vcpu);
> -	mutex_unlock(&vcpu->kvm->arch.config_lock);
> +		return __pkvm_create_hyp_vcpu(vcpu);
>  
> -	return ret;
> +	return 0;
>  }
>  
>  void pkvm_destroy_hyp_vm(struct kvm *kvm)
>  {
> -	mutex_lock(&kvm->arch.config_lock);
> +	guard(mutex)(&kvm->arch.config_lock);
>  	__pkvm_destroy_hyp_vm(kvm);
> -	mutex_unlock(&kvm->arch.config_lock);
>  }
>  
>  int pkvm_init_host_vm(struct kvm *kvm, unsigned long type)
> diff --git a/arch/arm64/kvm/psci.c b/arch/arm64/kvm/psci.c
> index 3b5dbe9a0a0e..e1389c525e9d 100644
> --- a/arch/arm64/kvm/psci.c
> +++ b/arch/arm64/kvm/psci.c
> @@ -62,7 +62,6 @@ static unsigned long kvm_psci_vcpu_on(struct kvm_vcpu *source_vcpu)
>  	struct vcpu_reset_state *reset_state;
>  	struct kvm *kvm = source_vcpu->kvm;
>  	struct kvm_vcpu *vcpu = NULL;
> -	int ret = PSCI_RET_SUCCESS;
>  	unsigned long cpu_id;
>  
>  	cpu_id = smccc_get_arg1(source_vcpu);
> @@ -78,14 +77,13 @@ static unsigned long kvm_psci_vcpu_on(struct kvm_vcpu *source_vcpu)
>  	if (!vcpu)
>  		return PSCI_RET_INVALID_PARAMS;
>  
> -	spin_lock(&vcpu->arch.mp_state_lock);
> +	guard(spinlock)(&vcpu->arch.mp_state_lock);
> +
>  	if (!kvm_arm_vcpu_stopped(vcpu)) {
>  		if (kvm_psci_version(source_vcpu) != KVM_ARM_PSCI_0_1)
> -			ret = PSCI_RET_ALREADY_ON;
> +			return PSCI_RET_ALREADY_ON;
>  		else
> -			ret = PSCI_RET_INVALID_PARAMS;
> -
> -		goto out_unlock;
> +			return PSCI_RET_INVALID_PARAMS;
>  	}
>  
>  	reset_state = &vcpu->arch.reset_state;
> @@ -113,9 +111,7 @@ static unsigned long kvm_psci_vcpu_on(struct kvm_vcpu *source_vcpu)
>  	WRITE_ONCE(vcpu->arch.mp_state.mp_state, KVM_MP_STATE_RUNNABLE);
>  	kvm_vcpu_wake_up(vcpu);
>  
> -out_unlock:
> -	spin_unlock(&vcpu->arch.mp_state_lock);
> -	return ret;
> +	return PSCI_RET_SUCCESS;
>  }
>  
>  static unsigned long kvm_psci_vcpu_affinity_info(struct kvm_vcpu *vcpu)
> @@ -176,9 +172,8 @@ static void kvm_prepare_system_event(struct kvm_vcpu *vcpu, u32 type, u64 flags)
>  	 * re-initialized.
>  	 */
>  	kvm_for_each_vcpu(i, tmp, vcpu->kvm) {
> -		spin_lock(&tmp->arch.mp_state_lock);
> +		guard(spinlock)(&tmp->arch.mp_state_lock);
>  		WRITE_ONCE(tmp->arch.mp_state.mp_state, KVM_MP_STATE_STOPPED);
> -		spin_unlock(&tmp->arch.mp_state_lock);
>  	}
>  	kvm_make_all_cpus_request(vcpu->kvm, KVM_REQ_SLEEP);
>  
> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> index b963fd975aac..60969d90bdd3 100644
> --- a/arch/arm64/kvm/reset.c
> +++ b/arch/arm64/kvm/reset.c
> @@ -193,10 +193,10 @@ void kvm_reset_vcpu(struct kvm_vcpu *vcpu)
>  	bool loaded;
>  	u32 pstate;
>  
> -	spin_lock(&vcpu->arch.mp_state_lock);
> -	reset_state = vcpu->arch.reset_state;
> -	vcpu->arch.reset_state.reset = false;
> -	spin_unlock(&vcpu->arch.mp_state_lock);
> +	scoped_guard(spinlock, &vcpu->arch.mp_state_lock) {
> +		reset_state = vcpu->arch.reset_state;
> +		vcpu->arch.reset_state.reset = false;
> +	}

Same, I don't find this one really interesting.

>  
>  	preempt_disable();
>  	loaded = (vcpu->cpu != -1);
> -- 
> 2.54.0.1136.gdb2ca164c4-goog
>