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SubjectRe: [PATCH v2 32/45] KVM: Move initialization of preempt notifier to kvm_vcpu_init()
On Wed, 18 Dec 2019 13:55:17 -0800
Sean Christopherson <sean.j.christopherson@intel.com> wrote:

> Initialize the preempt notifier immediately in kvm_vcpu_init() to pave
> the way for removing kvm_arch_vcpu_setup(), i.e. to allow arch specific
> code to call vcpu_load() during kvm_arch_vcpu_create().
>
> Back when preemption support was added, the location of the call to init
> the preempt notifier was perfectly sane. The overall vCPU creation flow
> featured a single arch specific hook and the preempt notifer was used
> immediately after its initialization (by vcpu_load()). E.g.:
>
> vcpu = kvm_arch_ops->vcpu_create(kvm, n);
> if (IS_ERR(vcpu))
> return PTR_ERR(vcpu);
>
> preempt_notifier_init(&vcpu->preempt_notifier, &kvm_preempt_ops);
>
> vcpu_load(vcpu);
> r = kvm_mmu_setup(vcpu);
> vcpu_put(vcpu);
> if (r < 0)
> goto free_vcpu;
>
> Today, the call to preempt_notifier_init() is sandwiched between two
> arch specific calls, kvm_arch_vcpu_create() and kvm_arch_vcpu_setup(),
> which needlessly forces x86 (and possibly others?) to split its vCPU
> creation flow. Init the preempt notifier prior to any arch specific
> call so that each arch can independently decide how best to organize
> its creation flow.
>
> Acked-by: Christoffer Dall <christoffer.dall@arm.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
> virt/kvm/kvm_main.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)

Reviewed-by: Cornelia Huck <cohuck@redhat.com>

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