Fix a semi theoretical race condition in reading of page_ready_pending in kvm_arch_async_page_present_queued. Only trust the value of page_ready_pending if the guest is about to enter guest mode (vcpu->mode). To achieve this, read the vcpu->mode using smp_load_acquire which is paired with smp_store_release in vcpu_enter_guest. Then only if vcpu_mode is IN_GUEST_MODE, trust the value of the page_ready_pending because it was written before and therefore its correct value is visible. Also if the above mentioned check is true, avoid raising the request on the target vCPU. Signed-off-by: Maxim Levitsky --- arch/x86/kvm/x86.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 9018d56b4b0a..3d45a4cd08a4 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -13459,9 +13459,14 @@ void kvm_arch_async_page_present(struct kvm_vcpu *vcpu, void kvm_arch_async_page_present_queued(struct kvm_vcpu *vcpu) { - kvm_make_request(KVM_REQ_APF_READY, vcpu); - if (!vcpu->arch.apf.pageready_pending) + /* Pairs with smp_store_release in vcpu_enter_guest. */ + bool in_guest_mode = (smp_load_acquire(&vcpu->mode) == IN_GUEST_MODE); + bool page_ready_pending = READ_ONCE(vcpu->arch.apf.pageready_pending); + + if (!in_guest_mode || !page_ready_pending) { + kvm_make_request(KVM_REQ_APF_READY, vcpu); kvm_vcpu_kick(vcpu); + } } bool kvm_arch_can_dequeue_async_page_present(struct kvm_vcpu *vcpu) -- 2.49.0