Revert "KVM: async_pf: Fix #DF due to inject "Page not Present" and "Page... (84b09f33) · Commits · 戴 / test

Revert "KVM: async_pf: Fix #DF due to inject "Page not Present" and "Page Ready" exceptions simultaneously" Commit (""KVM: async_pf: Fix #DF due to inject "Page not Present" and "Page Ready" exceptions simultaneously") added a protection against 'page ready' notification coming before 'page not present' is delivered. This situation seems to be impossible since commit ("KVM MMU: check pending exception before injecting APF) which added 'vcpu->arch.exception.pending' check to kvm_can_do_async_pf. On x86, kvm_arch_async_page_present() has only one call site: kvm_check_async_pf_completion() loop and we only enter the loop when kvm_arch_can_inject_async_page_present(vcpu) which when async pf msr is enabled, translates into kvm_can_do_async_pf(). There is also one problem with the cancellation mechanism. We don't seem to check that the 'page not present' notification we're canceling matches the 'page ready' notification so in theory, we may erroneously drop two valid events. Revert the commit. Reviewed-by:

Gavin Shan <gshan@redhat.com> Signed-off-by:

Vitaly Kuznetsov <vkuznets@redhat.com> Message-Id: <20200525144125.143875-2-vkuznets@redhat.com> Signed-off-by:

Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

+1 −22

Original line number	Diff line number	Diff line
		@@ -10427,13 +10427,6 @@ static int apf_put_user(struct kvm_vcpu *vcpu, u32 val)
		sizeof(val));
		}

		static int apf_get_user(struct kvm_vcpu vcpu, u32 val)
		{

		return kvm_read_guest_cached(vcpu->kvm, &vcpu->arch.apf.data, val,
		sizeof(u32));
		}

		static bool kvm_can_deliver_async_pf(struct kvm_vcpu *vcpu)
		{
		if (!vcpu->arch.apf.delivery_as_pf_vmexit && is_guest_mode(vcpu))
		@@ -10498,7 +10491,6 @@ void kvm_arch_async_page_present(struct kvm_vcpu *vcpu,
		struct kvm_async_pf *work)
		{
		struct x86_exception fault;
		u32 val;

		if (work->wakeup_all)
		work->arch.token = ~0; /* broadcast wakeup */
		@@ -10507,19 +10499,7 @@ void kvm_arch_async_page_present(struct kvm_vcpu *vcpu,
		trace_kvm_async_pf_ready(work->arch.token, work->cr2_or_gpa);

		if (vcpu->arch.apf.msr_val & KVM_ASYNC_PF_ENABLED &&
		!apf_get_user(vcpu, &val)) {
		if (val == KVM_PV_REASON_PAGE_NOT_PRESENT &&
		vcpu->arch.exception.pending &&
		vcpu->arch.exception.nr == PF_VECTOR &&
		!apf_put_user(vcpu, 0)) {
		vcpu->arch.exception.injected = false;
		vcpu->arch.exception.pending = false;
		vcpu->arch.exception.nr = 0;
		vcpu->arch.exception.has_error_code = false;
		vcpu->arch.exception.error_code = 0;
		vcpu->arch.exception.has_payload = false;
		vcpu->arch.exception.payload = 0;
		} else if (!apf_put_user(vcpu, KVM_PV_REASON_PAGE_READY)) {
		!apf_put_user(vcpu, KVM_PV_REASON_PAGE_READY)) {
		fault.vector = PF_VECTOR;
		fault.error_code_valid = true;
		fault.error_code = 0;
		@@ -10528,7 +10508,6 @@ void kvm_arch_async_page_present(struct kvm_vcpu *vcpu,
		fault.async_page_fault = true;
		kvm_inject_page_fault(vcpu, &fault);
		}
		}
		vcpu->arch.apf.halted = false;
		vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
		}

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