Re: [PATCH] KVM: x86: Convert INIT and SIPI signals into synchronously handled events

[Gleb Natapov <gleb@redhat.com>]

On Tue, Mar 12, 2013 at 02:21:17PM +0100, Jan Kiszka wrote:
> On 2013-03-12 14:12, Gleb Natapov wrote:
> > On Tue, Mar 12, 2013 at 12:44:41PM +0100, Jan Kiszka wrote:
> >> A VCPU sending INIT or SIPI to some other VCPU races for setting the
> >> remote VCPU's mp_state. When we were unlucky, KVM_MP_STATE_INIT_RECEIVED
> >> was overwritten by kvm_emulate_halt and, thus, got lost.
> >>
> >> This introduces APIC events for those two signals, keeping them in
> >> kvm_apic until kvm_apic_accept_events is run over the target vcpu
> >> context. kvm_apic_has_events reports to kvm_arch_vcpu_runnable if there
> >> are pending events, thus if vcpu blocking should end.
> >>
> >> The patch comes with the side effect of effectively obsoleting
> >> KVM_MP_STATE_SIPI_RECEIVED. We still accept it from user space, but
> >> immediately translate it to KVM_MP_STATE_INIT_RECEIVED + KVM_APIC_SIPI.
> >> The vcpu itself will no longer enter the KVM_MP_STATE_SIPI_RECEIVED
> >> state. That also means we no longer exit to user space after receiving a
> >> SIPI event.
> >>
> >> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> >> ---
> >>
> >> This doesn't fix the wrong behaviour on INIT for the BSP yet. Leaving
> >> this honor to Paolo.
> >>
> >> I didn't try porting any INIT handling for nested on top yet but I
> >> think it should be feasible - once we know their semantics for sure, at
> >> least on Intel...
> >>
> >>  arch/x86/include/asm/kvm_host.h |    1 +
> >>  arch/x86/kvm/lapic.c            |   41 +++++++++++++++++++++++++++++++-------
> >>  arch/x86/kvm/lapic.h            |    7 ++++++
> >>  arch/x86/kvm/x86.c              |   39 ++++++++++++++++++++----------------
> >>  4 files changed, 63 insertions(+), 25 deletions(-)
> >>
> >> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> >> index 348d859..2d28e76 100644
> >> --- a/arch/x86/include/asm/kvm_host.h
> >> +++ b/arch/x86/include/asm/kvm_host.h
> >> @@ -1002,6 +1002,7 @@ int kvm_cpu_has_injectable_intr(struct kvm_vcpu *v);
> >>  int kvm_cpu_has_interrupt(struct kvm_vcpu *vcpu);
> >>  int kvm_arch_interrupt_allowed(struct kvm_vcpu *vcpu);
> >>  int kvm_cpu_get_interrupt(struct kvm_vcpu *v);
> >> +void kvm_vcpu_reset(struct kvm_vcpu *vcpu);
> >>  
> >>  void kvm_define_shared_msr(unsigned index, u32 msr);
> >>  void kvm_set_shared_msr(unsigned index, u64 val, u64 mask);
> >> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> >> index 02b51dd..4a21a6b 100644
> >> --- a/arch/x86/kvm/lapic.c
> >> +++ b/arch/x86/kvm/lapic.c
> >> @@ -731,7 +731,7 @@ static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode,
> >>  	case APIC_DM_INIT:
> >>  		if (!trig_mode || level) {
> >>  			result = 1;
> >> -			vcpu->arch.mp_state = KVM_MP_STATE_INIT_RECEIVED;
> >> +			set_bit(KVM_APIC_INIT, &apic->pending_events);
> >>  			kvm_make_request(KVM_REQ_EVENT, vcpu);
> >>  			kvm_vcpu_kick(vcpu);
> >>  		} else {
> >> @@ -743,13 +743,13 @@ static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode,
> >>  	case APIC_DM_STARTUP:
> >>  		apic_debug("SIPI to vcpu %d vector 0x%02x\n",
> >>  			   vcpu->vcpu_id, vector);
> >> -		if (vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED) {
> >> -			result = 1;
> >> -			vcpu->arch.sipi_vector = vector;
> >> -			vcpu->arch.mp_state = KVM_MP_STATE_SIPI_RECEIVED;
> >> -			kvm_make_request(KVM_REQ_EVENT, vcpu);
> >> -			kvm_vcpu_kick(vcpu);
> >> -		}
> >> +		result = 1;
> >> +		apic->sipi_vector = vector;
> >> +		/* make sure sipi_vector is visible for the receiver */
> >> +		smp_wmb();
> >> +		set_bit(KVM_APIC_SIPI, &apic->pending_events);
> >> +		kvm_make_request(KVM_REQ_EVENT, vcpu);
> >> +		kvm_vcpu_kick(vcpu);
> >>  		break;
> >>  
> >>  	case APIC_DM_EXTINT:
> >> @@ -1860,6 +1860,31 @@ int kvm_lapic_enable_pv_eoi(struct kvm_vcpu *vcpu, u64 data)
> >>  					 addr);
> >>  }
> >>  
> >> +bool kvm_apic_has_events(struct kvm_vcpu *vcpu)
> >> +{
> >> +	return kvm_vcpu_has_lapic(vcpu) && vcpu->arch.apic->pending_events;
> > The function is called only from kvm_arch_vcpu_runnable() and
> > kvm_arch_vcpu_runnable() is called only if irqchip is in kernel, so I
> > think kvm_vcpu_has_lapic() can be dropped.
> 
> Likely, will check again.
> 
> > 
> >> +}
> >> +
> >> +void kvm_apic_accept_events(struct kvm_vcpu *vcpu)
> >> +{
> >> +	struct kvm_lapic *apic = vcpu->arch.apic;
> >> +
> >> +	if (!kvm_vcpu_has_lapic(vcpu))
> >> +		return;
> >> +
> >> +	if (test_and_clear_bit(KVM_APIC_INIT, &apic->pending_events))
> >> +		vcpu->arch.mp_state = KVM_MP_STATE_INIT_RECEIVED;
> >> +	if (test_and_clear_bit(KVM_APIC_SIPI, &apic->pending_events) &&
> >> +	    vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED) {
> >> +		vcpu->arch.sipi_vector = apic->sipi_vector;
> >> +		pr_debug("vcpu %d received sipi with vector # %x\n",
> >> +			 vcpu->vcpu_id, vcpu->arch.sipi_vector);
> >> +		kvm_lapic_reset(vcpu);
> >> +		kvm_vcpu_reset(vcpu);
> > Shouldn't we reset on KVM_APIC_INIT?
> 
> It is reset a few lines above. Yes, there could be another INIT pending
> by now, but that is racing with SIPI anyway and could also arrive a few
> instruction later. So I don't think we need to worry.
> 
Not sure I understand. I am saying the code should be:

if (test_and_clear_bit(KVM_APIC_INIT, &apic->pending_events)) {
	vcpu->arch.mp_state = KVM_MP_STATE_INIT_RECEIVED;
	kvm_lapic_reset(vcpu);
	kvm_vcpu_reset(vcpu);
}
if (test_and_clear_bit(KVM_APIC_SIPI, &apic->pending_events) &&
		vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED) {
	vcpu->arch.sipi_vector = apic->sipi_vector;
}

> > 
> >> +		vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
> >> +	}
> >> +}
> >> +
> >>  void kvm_lapic_init(void)
> >>  {
> >>  	/* do not patch jump label more than once per second */
> >> diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
> >> index 1676d34..ef3f4ef 100644
> >> --- a/arch/x86/kvm/lapic.h
> >> +++ b/arch/x86/kvm/lapic.h
> >> @@ -5,6 +5,9 @@
> >>  
> >>  #include <linux/kvm_host.h>
> >>  
> >> +#define KVM_APIC_INIT		0
> >> +#define KVM_APIC_SIPI		1
> >> +
> >>  struct kvm_timer {
> >>  	struct hrtimer timer;
> >>  	s64 period; 				/* unit: ns */
> >> @@ -32,13 +35,17 @@ struct kvm_lapic {
> >>  	void *regs;
> >>  	gpa_t vapic_addr;
> >>  	struct page *vapic_page;
> >> +	unsigned long pending_events;
> >> +	unsigned int sipi_vector;
> >>  };
> >>  int kvm_create_lapic(struct kvm_vcpu *vcpu);
> >>  void kvm_free_lapic(struct kvm_vcpu *vcpu);
> >>  
> >>  int kvm_apic_has_interrupt(struct kvm_vcpu *vcpu);
> >> +bool kvm_apic_has_events(struct kvm_vcpu *vcpu);
> >>  int kvm_apic_accept_pic_intr(struct kvm_vcpu *vcpu);
> >>  int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu);
> >> +void kvm_apic_accept_events(struct kvm_vcpu *vcpu);
> >>  void kvm_lapic_reset(struct kvm_vcpu *vcpu);
> >>  u64 kvm_lapic_get_cr8(struct kvm_vcpu *vcpu);
> >>  void kvm_lapic_set_tpr(struct kvm_vcpu *vcpu, unsigned long cr8);
> >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> >> index b891ac3..a0b8041 100644
> >> --- a/arch/x86/kvm/x86.c
> >> +++ b/arch/x86/kvm/x86.c
> >> @@ -162,8 +162,6 @@ u64 __read_mostly host_xcr0;
> >>  
> >>  static int emulator_fix_hypercall(struct x86_emulate_ctxt *ctxt);
> >>  
> >> -static void kvm_vcpu_reset(struct kvm_vcpu *vcpu);
> >> -
> >>  static inline void kvm_async_pf_hash_reset(struct kvm_vcpu *vcpu)
> >>  {
> >>  	int i;
> >> @@ -5663,6 +5661,11 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> >>  	bool req_immediate_exit = 0;
> >>  
> >>  	if (vcpu->requests) {
> >> +		kvm_apic_accept_events(vcpu);
> >> +		if (vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED) {
> >> +			r = 1;
> >> +			goto out;
> >> +		}
> > Why not call it under kvm_check_request(KVM_REQ_EVENT, vcpu) bellow?
> 
> I probably had the desire to handle this event and potential exit reason
> early. Not sure if it makes any difference.
> 
It shouldn't, so better to handle with all other apic events.

--
			Gleb.