Commit ec0671d5 authored by Wanpeng Li's avatar Wanpeng Li Committed by Paolo Bonzini
Browse files

KVM: LAPIC: Delay trace_kvm_wait_lapic_expire tracepoint to after vmexit 

wait_lapic_expire() call was moved above guest_enter_irqoff() because of
its tracepoint, which violated the RCU extended quiescent state invoked
by guest_enter_irqoff()[1][2]. This patch simply moves the tracepoint
below guest_exit_irqoff() in vcpu_enter_guest(). Snapshot the delta before
VM-Enter, but trace it after VM-Exit. This can help us to move
wait_lapic_expire() just before vmentry in the later patch.

[1] Commit 8b89fe1f ("kvm: x86: move tracepoints outside extended quiescent state")
[2] https://patchwork.kernel.org/patch/7821111/



Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Liran Alon <liran.alon@oracle.com>
Suggested-by: default avatarSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: default avatarWanpeng Li <wanpengli@tencent.com>
[Track whether wait_lapic_expire was called, and do not invoke the tracepoint
 if not. - Paolo]
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 84ea3aca

arch/x86/kvm/lapic.c

+7 −7
Original line number Diff line number Diff line
@@ -1502,27 +1502,27 @@ static inline void __wait_lapic_expire(struct kvm_vcpu *vcpu, u64 guest_cycles) 
}



static inline void adjust_lapic_timer_advance(struct kvm_vcpu *vcpu,

					      u64 guest_tsc, u64 tsc_deadline)

					      s64 advance_expire_delta)

{

	struct kvm_lapic *apic = vcpu->arch.apic;

	u32 timer_advance_ns = apic->lapic_timer.timer_advance_ns;

	u64 ns;



	/* too early */

	if (guest_tsc < tsc_deadline) {

		ns = (tsc_deadline - guest_tsc) * 1000000ULL;

	if (advance_expire_delta < 0) {

		ns = -advance_expire_delta * 1000000ULL;

		do_div(ns, vcpu->arch.virtual_tsc_khz);

		timer_advance_ns -= min((u32)ns,

			timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP);

	} else {

	/* too late */

		ns = (guest_tsc - tsc_deadline) * 1000000ULL;

		ns = advance_expire_delta * 1000000ULL;

		do_div(ns, vcpu->arch.virtual_tsc_khz);

		timer_advance_ns += min((u32)ns,

			timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP);

	}



	if (abs(guest_tsc - tsc_deadline) < LAPIC_TIMER_ADVANCE_ADJUST_DONE)

	if (abs(advance_expire_delta) < LAPIC_TIMER_ADVANCE_ADJUST_DONE)

		apic->lapic_timer.timer_advance_adjust_done = true;

	if (unlikely(timer_advance_ns > 5000)) {

		timer_advance_ns = 0;
@@ -1545,13 +1545,13 @@ void wait_lapic_expire(struct kvm_vcpu *vcpu) 
	tsc_deadline = apic->lapic_timer.expired_tscdeadline;

	apic->lapic_timer.expired_tscdeadline = 0;

	guest_tsc = kvm_read_l1_tsc(vcpu, rdtsc());

	trace_kvm_wait_lapic_expire(vcpu->vcpu_id, guest_tsc - tsc_deadline);

	apic->lapic_timer.advance_expire_delta = guest_tsc - tsc_deadline;



	if (guest_tsc < tsc_deadline)

		__wait_lapic_expire(vcpu, tsc_deadline - guest_tsc);



	if (unlikely(!apic->lapic_timer.timer_advance_adjust_done))

		adjust_lapic_timer_advance(vcpu, guest_tsc, tsc_deadline);

		adjust_lapic_timer_advance(vcpu, apic->lapic_timer.advance_expire_delta);

}



static void start_sw_tscdeadline(struct kvm_lapic *apic)

arch/x86/kvm/lapic.h

+1 −0
Original line number Diff line number Diff line
@@ -32,6 +32,7 @@ struct kvm_timer { 
	u64 tscdeadline;

	u64 expired_tscdeadline;

	u32 timer_advance_ns;

	s64 advance_expire_delta;

	atomic_t pending;			/* accumulated triggered timers */

	bool hv_timer_in_use;

	bool timer_advance_adjust_done;

arch/x86/kvm/x86.c

+7 −0
Original line number Diff line number Diff line
@@ -7980,6 +7980,13 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) 
	++vcpu->stat.exits;



	guest_exit_irqoff();

	if (lapic_in_kernel(vcpu)) {

		s64 delta = vcpu->arch.apic->lapic_timer.advance_expire_delta;

		if (delta != S64_MIN) {

			trace_kvm_wait_lapic_expire(vcpu->vcpu_id, delta);

			vcpu->arch.apic->lapic_timer.advance_expire_delta = S64_MIN;

		}

	}



	local_irq_enable();

	preempt_enable();

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