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

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2013-03-12 13:58, Jan Kiszka wrote:
> On 2013-03-12 13:06, Paolo Bonzini wrote:
>> Il 12/03/2013 12:44, Jan Kiszka ha scritto:
>>> 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);
>>
>> I think this should clear pending SIPIs, unless KVM_APIC_INIT was
>> already set in which case it should be a no-op.  Something like:
>>
>> 	e = apic->pending_events;
>> 	while (!(e & KVM_APIC_INIT))
>> 		e = cmpxchg(&apic->pending_events, e,
>> 			    (e | KVM_APIC_INIT) & ~KVM_APIC_SIPI);
>>
>> If you do this, better make pending_events an atomic_t.
> 
> OK (looks ugly but necessary).
> 
>>
>>>  			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;
>>> +}
>>> +
>>> +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);
>>> +		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;
>>> +		}
>>>  		if (kvm_check_request(KVM_REQ_MMU_RELOAD, vcpu))
>>>  			kvm_mmu_unload(vcpu);
>>>  		if (kvm_check_request(KVM_REQ_MIGRATE_TIMER, vcpu))
>>> @@ -5847,14 +5850,6 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
>>>  	int r;
>>>  	struct kvm *kvm = vcpu->kvm;
>>>  
>>> -	if (unlikely(vcpu->arch.mp_state == KVM_MP_STATE_SIPI_RECEIVED)) {
>>> -		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);
>>> -		vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
>>> -	}
>>> -
>>>  	vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
>>>  	r = vapic_enter(vcpu);
>>>  	if (r) {
>>> @@ -5871,8 +5866,8 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
>>>  			srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
>>>  			kvm_vcpu_block(vcpu);
>>>  			vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
>>> -			if (kvm_check_request(KVM_REQ_UNHALT, vcpu))
>>> -			{
>>> +			if (kvm_check_request(KVM_REQ_UNHALT, vcpu)) {
>>> +				kvm_apic_accept_events(vcpu);
>>>  				switch(vcpu->arch.mp_state) {
>>>  				case KVM_MP_STATE_HALTED:
>>>  					vcpu->arch.mp_state =
>>> @@ -5880,7 +5875,8 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
>>>  				case KVM_MP_STATE_RUNNABLE:
>>>  					vcpu->arch.apf.halted = false;
>>>  					break;
>>> -				case KVM_MP_STATE_SIPI_RECEIVED:
>>> +				case KVM_MP_STATE_INIT_RECEIVED:
>>> +					break;
>>>  				default:
>>>  					r = -EINTR;
>>>  					break;
>>> @@ -5901,7 +5897,8 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
>>>  			++vcpu->stat.request_irq_exits;
>>>  		}
>>>  
>>> -		kvm_check_async_pf_completion(vcpu);
>>> +		if (vcpu->arch.mp_state != KVM_MP_STATE_INIT_RECEIVED)
>>> +			kvm_check_async_pf_completion(vcpu);
>>
>> Can you instead do another change that affects the conditions of
>> kvm_check_async_pf_completion?
>>
>> For example, should kvm_arch_interrupt_allowed return zero if the VCPU
>> is in the INIT_RECEIVED state?
> 
> Yeah, that probably makes sense beyond async_pf.

Wait: If you perform a proper reset on INIT already, we would clear IF
thus prevent also async_pf injections. On the other hand,
kvm_arch_can_inject_async_page_present returns true if apf.msr_val &
KVM_ASYNC_PF_ENABLED is not set - shouldn't that be cleared on reset as
well? Hmm...

Jan

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