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

David Hildenbrand
2017-08-22T11:51:47Z

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.

--

Thanks,

David