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

Jan Kiszka
2013-03-12T12:58:54Z

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.

>
>>
>> if (signal_pending(current)) {
>> r = -EINTR;
>> @@ -6015,6 +6012,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>>
>> if (unlikely(vcpu->arch.mp_state == KVM_MP_STATE_UNINITIALIZED)) {
>> kvm_vcpu_block(vcpu);
>> + kvm_apic_accept_events(vcpu);
>> clear_bit(KVM_REQ_UNHALT, &vcpu->requests);
>> r = -EAGAIN;
>> goto out;
>> @@ -6171,6 +6169,7 @@ int kvm_arch_vcpu_ioctl_get_sregs(struct kvm_vcpu *vcpu,
>> int kvm_arch_vcpu_ioctl_get_mpstate(struct kvm_vcpu *vcpu,
>> struct kvm_mp_state *mp_state)
>> {
>> + kvm_apic_accept_events(vcpu);
>
> Is this racy against __vcpu_run?

No, as Gleb already explained.

>
>> mp_state->mp_state = vcpu->arch.mp_state;
>> return 0;
>> }
>> @@ -6178,7 +6177,13 @@ int kvm_arch_vcpu_ioctl_get_mpstate(struct kvm_vcpu *vcpu,
>> int kvm_arch_vcpu_ioctl_set_mpstate(struct kvm_vcpu *vcpu,
>> struct kvm_mp_state *mp_state)
>> {
>> - vcpu->arch.mp_state = mp_state->mp_state;
>> + if (mp_state->mp_state == KVM_MP_STATE_SIPI_RECEIVED) {
>> + if (!kvm_vcpu_has_lapic(vcpu))
>> + return -EINVAL;
>> + vcpu->arch.mp_state = KVM_MP_STATE_INIT_RECEIVED;
>> + set_bit(KVM_APIC_SIPI, &vcpu->arch.apic->pending_events);
>> + } else
>> + vcpu->arch.mp_state = mp_state->mp_state;
>
> Should INIT_RECEIVED also be invalid without an in-kernel LAPIC?

Good question. But, then, how do we reset those CPUs (BSPs only)?

Jan

--
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