Commit d2060bd4 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

KVM: nVMX: Open a window for pending nested VMX preemption timer 



Add a kvm_x86_ops hook to detect a nested pending "hypervisor timer" and
use it to effectively open a window for servicing the expired timer.
Like pending SMIs on VMX, opening a window simply means requesting an
immediate exit.

This fixes a bug where an expired VMX preemption timer (for L2) will be
delayed and/or lost if a pending exception is injected into L2.  The
pending exception is rightly prioritized by vmx_check_nested_events()
and injected into L2, with the preemption timer left pending.  Because
no window opened, L2 is free to run uninterrupted.

Fixes: f4124500 ("KVM: nVMX: Fully emulate preemption timer")
Reported-by: default avatarJim Mattson <jmattson@google.com>
Cc: Oliver Upton <oupton@google.com>
Cc: Peter Shier <pshier@google.com>
Signed-off-by: default avatarSean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200423022550.15113-3-sean.j.christopherson@intel.com>
[Check it in kvm_vcpu_has_events too, to ensure that the preemption
 timer is serviced promptly even if the vCPU is halted and L1 is not
 intercepting HLT. - Paolo]
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 6ce347af

arch/x86/include/asm/kvm_host.h

+1 −0
Original line number Diff line number Diff line
@@ -1256,6 +1256,7 @@ struct kvm_x86_ops { 


struct kvm_x86_nested_ops {

	int (*check_events)(struct kvm_vcpu *vcpu);

	bool (*hv_timer_pending)(struct kvm_vcpu *vcpu);

	int (*get_state)(struct kvm_vcpu *vcpu,

			 struct kvm_nested_state __user *user_kvm_nested_state,

			 unsigned user_data_size);

arch/x86/kvm/vmx/nested.c

+8 −2
Original line number Diff line number Diff line
@@ -3687,6 +3687,12 @@ static void nested_vmx_update_pending_dbg(struct kvm_vcpu *vcpu) 
			    vcpu->arch.exception.payload);

}



static bool nested_vmx_preemption_timer_pending(struct kvm_vcpu *vcpu)

{

	return nested_cpu_has_preemption_timer(get_vmcs12(vcpu)) &&

	       to_vmx(vcpu)->nested.preemption_timer_expired;

}



static int vmx_check_nested_events(struct kvm_vcpu *vcpu)

{

	struct vcpu_vmx *vmx = to_vmx(vcpu);
@@ -3742,8 +3748,7 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu) 
		return 0;

	}



	if (nested_cpu_has_preemption_timer(get_vmcs12(vcpu)) &&

	    vmx->nested.preemption_timer_expired) {

	if (nested_vmx_preemption_timer_pending(vcpu)) {

		if (block_nested_events)

			return -EBUSY;

		nested_vmx_vmexit(vcpu, EXIT_REASON_PREEMPTION_TIMER, 0, 0);
@@ -6448,6 +6453,7 @@ __init int nested_vmx_hardware_setup(struct kvm_x86_ops *ops, 


struct kvm_x86_nested_ops vmx_nested_ops = {

	.check_events = vmx_check_nested_events,

	.hv_timer_pending = nested_vmx_preemption_timer_pending,

	.get_state = vmx_get_nested_state,

	.set_state = vmx_set_nested_state,

	.get_vmcs12_pages = nested_get_vmcs12_pages,

arch/x86/kvm/x86.c

+9 −0
Original line number Diff line number Diff line
@@ -8355,6 +8355,10 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) 
				kvm_x86_ops.enable_nmi_window(vcpu);

			if (kvm_cpu_has_injectable_intr(vcpu) || req_int_win)

				kvm_x86_ops.enable_irq_window(vcpu);

			if (is_guest_mode(vcpu) &&

			    kvm_x86_ops.nested_ops->hv_timer_pending &&

			    kvm_x86_ops.nested_ops->hv_timer_pending(vcpu))

				req_immediate_exit = true;

			WARN_ON(vcpu->arch.exception.pending);

		}
@@ -10211,6 +10215,11 @@ static inline bool kvm_vcpu_has_events(struct kvm_vcpu *vcpu) 
	if (kvm_hv_has_stimer_pending(vcpu))

		return true;



	if (is_guest_mode(vcpu) &&

	    kvm_x86_ops.nested_ops->hv_timer_pending &&

	    kvm_x86_ops.nested_ops->hv_timer_pending(vcpu))

		return true;



	return false;

}

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