KVM: arm/arm64: properly use vcpu requests

arm/arm64 already has one VCPU request used when setting pause,
but it doesn't properly check requests in VCPU RUN. Check it
and also make sure we set vcpu->mode at the appropriate time
(before the check) and with the appropriate barriers. See
Documentation/virtual/kvm/vcpu-requests.rst. Also make sure we
don't leave any vcpu requests we don't intend to handle later
set in the request bitmap. If we don't clear them, then
kvm_request_pending() may return true when it shouldn't.

Using VCPU requests properly fixes a small race where pause
could get set just as a VCPU was entering guest mode.
Signed-off-by: Andrew Jones <drjones@redhat.com>
Reviewed-by: Christoffer Dall <cdall@linaro.org>
Signed-off-by: Christoffer Dall <cdall@linaro.org>

arch/arm/kvm/handle_exit.c

@@ -72,6 +72,7 @@ static int kvm_handle_wfx(struct kvm_vcpu *vcpu, struct kvm_run *run)
 		trace_kvm_wfx(*vcpu_pc(vcpu), false);
 		vcpu->stat.wfi_exit_stat++;
 		kvm_vcpu_block(vcpu);
+		kvm_clear_request(KVM_REQ_UNHALT, vcpu);
 	}
 
 	kvm_skip_instr(vcpu, kvm_vcpu_trap_il_is32bit(vcpu));

arch/arm64/kvm/handle_exit.c

@@ -89,6 +89,7 @@ static int kvm_handle_wfx(struct kvm_vcpu *vcpu, struct kvm_run *run)
 		trace_kvm_wfx_arm64(*vcpu_pc(vcpu), false);
 		vcpu->stat.wfi_exit_stat++;
 		kvm_vcpu_block(vcpu);
+		kvm_clear_request(KVM_REQ_UNHALT, vcpu);
 	}
 
 	kvm_skip_instr(vcpu, kvm_vcpu_trap_il_is32bit(vcpu));

virt/kvm/arm/arm.c

@@ -546,6 +546,7 @@ void kvm_arm_resume_guest(struct kvm *kvm)
 
 	kvm_for_each_vcpu(i, vcpu, kvm) {
 		vcpu->arch.pause = false;
+		kvm_clear_request(KVM_REQ_VCPU_EXIT, vcpu);
 		swake_up(kvm_arch_vcpu_wq(vcpu));
 	}
 }
@@ -638,8 +639,18 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
 			run->exit_reason = KVM_EXIT_INTR;
 		}
 
+		/*
+		 * Ensure we set mode to IN_GUEST_MODE after we disable
+		 * interrupts and before the final VCPU requests check.
+		 * See the comment in kvm_vcpu_exiting_guest_mode() and
+		 * Documentation/virtual/kvm/vcpu-requests.rst
+		 */
+		smp_store_mb(vcpu->mode, IN_GUEST_MODE);
+
 		if (ret <= 0 || need_new_vmid_gen(vcpu->kvm) ||
+		    kvm_request_pending(vcpu) ||
 		    vcpu->arch.power_off || vcpu->arch.pause) {
+			vcpu->mode = OUTSIDE_GUEST_MODE;
 			local_irq_enable();
 			kvm_pmu_sync_hwstate(vcpu);
 			kvm_timer_sync_hwstate(vcpu);
@@ -655,7 +666,6 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
 		 */
 		trace_kvm_entry(*vcpu_pc(vcpu));
 		guest_enter_irqoff();
-		vcpu->mode = IN_GUEST_MODE;
 
 		ret = kvm_call_hyp(__kvm_vcpu_run, vcpu);
 

virt/kvm/arm/psci.c

@@ -57,6 +57,7 @@ static unsigned long kvm_psci_vcpu_suspend(struct kvm_vcpu *vcpu)
 	 * for KVM will preserve the register state.
 	 */
 	kvm_vcpu_block(vcpu);
+	kvm_clear_request(KVM_REQ_UNHALT, vcpu);
 
 	return PSCI_RET_SUCCESS;
 }