[RFC,v3,4/9] KVM: arm/arm64: use locking helpers in kvm_vgic_create()

Message ID 20170821203530.9266-5-rkrcmar@redhat.com
State Changes Requested
Headers show

Commit Message

Radim Krčmář Aug. 21, 2017, 8:35 p.m.
No new VCPUs can be created because we are holding the kvm->lock.
This means that if we successfuly lock all VCPUs, we'll be unlocking the
same set and there is no need to do extra bookkeeping.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
 virt/kvm/arm/vgic/vgic-init.c       | 24 +++++++++---------------
 virt/kvm/arm/vgic/vgic-kvm-device.c |  6 +++++-
 2 files changed, 14 insertions(+), 16 deletions(-)

Comments

David Hildenbrand Aug. 22, 2017, 11:51 a.m. | #1
On 21.08.2017 22:35, Radim Krčmář wrote:
> No new VCPUs can be created because we are holding the kvm->lock.
> This means that if we successfuly lock all VCPUs, we'll be unlocking the
> same set and there is no need to do extra bookkeeping.
> 
> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
> ---
>  virt/kvm/arm/vgic/vgic-init.c       | 24 +++++++++---------------
>  virt/kvm/arm/vgic/vgic-kvm-device.c |  6 +++++-
>  2 files changed, 14 insertions(+), 16 deletions(-)
> 
> diff --git a/virt/kvm/arm/vgic/vgic-init.c b/virt/kvm/arm/vgic/vgic-init.c
> index 5801261f3add..feb766f74c34 100644
> --- a/virt/kvm/arm/vgic/vgic-init.c
> +++ b/virt/kvm/arm/vgic/vgic-init.c
> @@ -119,7 +119,7 @@ void kvm_vgic_vcpu_early_init(struct kvm_vcpu *vcpu)
>   */
>  int kvm_vgic_create(struct kvm *kvm, u32 type)
>  {
> -	int i, vcpu_lock_idx = -1, ret;
> +	int i, ret;
>  	struct kvm_vcpu *vcpu;
>  
>  	if (irqchip_in_kernel(kvm))
> @@ -140,18 +140,14 @@ int kvm_vgic_create(struct kvm *kvm, u32 type)
>  	 * vcpu->mutex.  By grabbing the vcpu->mutex of all VCPUs we ensure
>  	 * that no other VCPUs are run while we create the vgic.
>  	 */
> -	ret = -EBUSY;
> -	kvm_for_each_vcpu(i, vcpu, kvm) {
> -		if (!mutex_trylock(&vcpu->mutex))
> -			goto out_unlock;
> -		vcpu_lock_idx = i;
> -	}
> +	if (!lock_all_vcpus(kvm))
> +		return -EBUSY;

Yes, this makes sense.

>  
> -	kvm_for_each_vcpu(i, vcpu, kvm) {
> -		if (vcpu->arch.has_run_once)
> +	kvm_for_each_vcpu(i, vcpu, kvm)
> +		if (vcpu->arch.has_run_once) {
> +			ret = -EBUSY;
>  			goto out_unlock;
> -	}
> -	ret = 0;
> +		}

somehow I prefer keeping the {}

>  
>  	if (type == KVM_DEV_TYPE_ARM_VGIC_V2)
>  		kvm->arch.max_vcpus = VGIC_V2_MAX_CPUS;
> @@ -176,11 +172,9 @@ int kvm_vgic_create(struct kvm *kvm, u32 type)
>  	kvm->arch.vgic.vgic_cpu_base = VGIC_ADDR_UNDEF;
>  	kvm->arch.vgic.vgic_redist_base = VGIC_ADDR_UNDEF;
>  
> +	ret = 0;
>  out_unlock:
> -	for (; vcpu_lock_idx >= 0; vcpu_lock_idx--) {
> -		vcpu = kvm_get_vcpu(kvm, vcpu_lock_idx);
> -		mutex_unlock(&vcpu->mutex);
> -	}
> +	unlock_all_vcpus(kvm);
>  	return ret;
>  }
>  
> diff --git a/virt/kvm/arm/vgic/vgic-kvm-device.c b/virt/kvm/arm/vgic/vgic-kvm-device.c
> index 10ae6f394b71..c5124737c7fc 100644
> --- a/virt/kvm/arm/vgic/vgic-kvm-device.c
> +++ b/virt/kvm/arm/vgic/vgic-kvm-device.c
> @@ -270,7 +270,11 @@ static void unlock_vcpus(struct kvm *kvm, int vcpu_lock_idx)
>  
>  void unlock_all_vcpus(struct kvm *kvm)
>  {
> -	unlock_vcpus(kvm, atomic_read(&kvm->online_vcpus) - 1);
> +	int i;
> +	struct kvm_vcpu *tmp_vcpu;
> +
> +	kvm_for_each_vcpu(i, tmp_vcpu, kvm)
> +		mutex_unlock(&tmp_vcpu->mutex);
>  }
>  
>  /* Returns true if all vcpus were locked, false otherwise */
> 

Looks sane to me.
Christoffer Dall Aug. 29, 2017, 10 a.m. | #2
On Mon, Aug 21, 2017 at 10:35:25PM +0200, Radim Krčmář wrote:
> No new VCPUs can be created because we are holding the kvm->lock.
> This means that if we successfuly lock all VCPUs, we'll be unlocking the
> same set and there is no need to do extra bookkeeping.
> 
> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
> ---
>  virt/kvm/arm/vgic/vgic-init.c       | 24 +++++++++---------------
>  virt/kvm/arm/vgic/vgic-kvm-device.c |  6 +++++-
>  2 files changed, 14 insertions(+), 16 deletions(-)
> 
> diff --git a/virt/kvm/arm/vgic/vgic-init.c b/virt/kvm/arm/vgic/vgic-init.c
> index 5801261f3add..feb766f74c34 100644
> --- a/virt/kvm/arm/vgic/vgic-init.c
> +++ b/virt/kvm/arm/vgic/vgic-init.c
> @@ -119,7 +119,7 @@ void kvm_vgic_vcpu_early_init(struct kvm_vcpu *vcpu)
>   */
>  int kvm_vgic_create(struct kvm *kvm, u32 type)
>  {
> -	int i, vcpu_lock_idx = -1, ret;
> +	int i, ret;
>  	struct kvm_vcpu *vcpu;
>  
>  	if (irqchip_in_kernel(kvm))
> @@ -140,18 +140,14 @@ int kvm_vgic_create(struct kvm *kvm, u32 type)
>  	 * vcpu->mutex.  By grabbing the vcpu->mutex of all VCPUs we ensure
>  	 * that no other VCPUs are run while we create the vgic.
>  	 */
> -	ret = -EBUSY;
> -	kvm_for_each_vcpu(i, vcpu, kvm) {
> -		if (!mutex_trylock(&vcpu->mutex))
> -			goto out_unlock;
> -		vcpu_lock_idx = i;
> -	}
> +	if (!lock_all_vcpus(kvm))
> +		return -EBUSY;
>  
> -	kvm_for_each_vcpu(i, vcpu, kvm) {
> -		if (vcpu->arch.has_run_once)
> +	kvm_for_each_vcpu(i, vcpu, kvm)
> +		if (vcpu->arch.has_run_once) {
> +			ret = -EBUSY;
>  			goto out_unlock;
> -	}
> -	ret = 0;
> +		}

I also prefer the additional brace here.

>  
>  	if (type == KVM_DEV_TYPE_ARM_VGIC_V2)
>  		kvm->arch.max_vcpus = VGIC_V2_MAX_CPUS;
> @@ -176,11 +172,9 @@ int kvm_vgic_create(struct kvm *kvm, u32 type)
>  	kvm->arch.vgic.vgic_cpu_base = VGIC_ADDR_UNDEF;
>  	kvm->arch.vgic.vgic_redist_base = VGIC_ADDR_UNDEF;
>  
> +	ret = 0;
>  out_unlock:
> -	for (; vcpu_lock_idx >= 0; vcpu_lock_idx--) {
> -		vcpu = kvm_get_vcpu(kvm, vcpu_lock_idx);
> -		mutex_unlock(&vcpu->mutex);
> -	}
> +	unlock_all_vcpus(kvm);
>  	return ret;
>  }
>  
> diff --git a/virt/kvm/arm/vgic/vgic-kvm-device.c b/virt/kvm/arm/vgic/vgic-kvm-device.c
> index 10ae6f394b71..c5124737c7fc 100644
> --- a/virt/kvm/arm/vgic/vgic-kvm-device.c
> +++ b/virt/kvm/arm/vgic/vgic-kvm-device.c
> @@ -270,7 +270,11 @@ static void unlock_vcpus(struct kvm *kvm, int vcpu_lock_idx)
>  
>  void unlock_all_vcpus(struct kvm *kvm)
>  {
> -	unlock_vcpus(kvm, atomic_read(&kvm->online_vcpus) - 1);
> +	int i;
> +	struct kvm_vcpu *tmp_vcpu;
> +
> +	kvm_for_each_vcpu(i, tmp_vcpu, kvm)
> +		mutex_unlock(&tmp_vcpu->mutex);
>  }
>  
>  /* Returns true if all vcpus were locked, false otherwise */
> -- 
> 2.13.3
> 

As noted on the other patch, it looks a bit strange to modify
unlock_all_vcpus() here without also doing something about the error
path in lock_all_vcpus().

Otherwise this patch looks fine to me.

Thanks,
-Christoffer
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Patch

diff --git a/virt/kvm/arm/vgic/vgic-init.c b/virt/kvm/arm/vgic/vgic-init.c
index 5801261f3add..feb766f74c34 100644
--- a/virt/kvm/arm/vgic/vgic-init.c
+++ b/virt/kvm/arm/vgic/vgic-init.c
@@ -119,7 +119,7 @@  void kvm_vgic_vcpu_early_init(struct kvm_vcpu *vcpu)
  */
 int kvm_vgic_create(struct kvm *kvm, u32 type)
 {
-	int i, vcpu_lock_idx = -1, ret;
+	int i, ret;
 	struct kvm_vcpu *vcpu;
 
 	if (irqchip_in_kernel(kvm))
@@ -140,18 +140,14 @@  int kvm_vgic_create(struct kvm *kvm, u32 type)
 	 * vcpu->mutex.  By grabbing the vcpu->mutex of all VCPUs we ensure
 	 * that no other VCPUs are run while we create the vgic.
 	 */
-	ret = -EBUSY;
-	kvm_for_each_vcpu(i, vcpu, kvm) {
-		if (!mutex_trylock(&vcpu->mutex))
-			goto out_unlock;
-		vcpu_lock_idx = i;
-	}
+	if (!lock_all_vcpus(kvm))
+		return -EBUSY;
 
-	kvm_for_each_vcpu(i, vcpu, kvm) {
-		if (vcpu->arch.has_run_once)
+	kvm_for_each_vcpu(i, vcpu, kvm)
+		if (vcpu->arch.has_run_once) {
+			ret = -EBUSY;
 			goto out_unlock;
-	}
-	ret = 0;
+		}
 
 	if (type == KVM_DEV_TYPE_ARM_VGIC_V2)
 		kvm->arch.max_vcpus = VGIC_V2_MAX_CPUS;
@@ -176,11 +172,9 @@  int kvm_vgic_create(struct kvm *kvm, u32 type)
 	kvm->arch.vgic.vgic_cpu_base = VGIC_ADDR_UNDEF;
 	kvm->arch.vgic.vgic_redist_base = VGIC_ADDR_UNDEF;
 
+	ret = 0;
 out_unlock:
-	for (; vcpu_lock_idx >= 0; vcpu_lock_idx--) {
-		vcpu = kvm_get_vcpu(kvm, vcpu_lock_idx);
-		mutex_unlock(&vcpu->mutex);
-	}
+	unlock_all_vcpus(kvm);
 	return ret;
 }
 
diff --git a/virt/kvm/arm/vgic/vgic-kvm-device.c b/virt/kvm/arm/vgic/vgic-kvm-device.c
index 10ae6f394b71..c5124737c7fc 100644
--- a/virt/kvm/arm/vgic/vgic-kvm-device.c
+++ b/virt/kvm/arm/vgic/vgic-kvm-device.c
@@ -270,7 +270,11 @@  static void unlock_vcpus(struct kvm *kvm, int vcpu_lock_idx)
 
 void unlock_all_vcpus(struct kvm *kvm)
 {
-	unlock_vcpus(kvm, atomic_read(&kvm->online_vcpus) - 1);
+	int i;
+	struct kvm_vcpu *tmp_vcpu;
+
+	kvm_for_each_vcpu(i, tmp_vcpu, kvm)
+		mutex_unlock(&tmp_vcpu->mutex);
 }
 
 /* Returns true if all vcpus were locked, false otherwise */