On Wed, Mar 13, 2013 at 12:42:34PM +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.
>
> Furthermore, we already reset the VCPU on INIT, only fixing up the code
> segment later on when SIPI arrives. Moreover, we fix INIT handling for
> the BSP: it never enter wait-for-SIPI but directly starts over on INIT.
>
> Signed-off-by: Jan Kiszka <jan.kis...@siemens.com>
> ---
>
> Changes in v2:
> - drop cmpxchg from INIT signaling
> - rmb on SIPI processing
> - reset sets all CPUs to 0xf000:0xfff0, RIP is fixed up on SIPI reception
>
> arch/x86/include/asm/kvm_host.h | 3 +-
> arch/x86/kvm/lapic.c | 48 +++++++++++++++++++++++++++-----
> arch/x86/kvm/lapic.h | 11 +++++++
> arch/x86/kvm/svm.c | 6 ----
> arch/x86/kvm/vmx.c | 12 +-------
> arch/x86/kvm/x86.c | 58 +++++++++++++++++++++++++-------------
> 6 files changed, 93 insertions(+), 45 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 348d859..ef7f4a5 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -345,7 +345,6 @@ struct kvm_vcpu_arch {
> unsigned long apic_attention;
> int32_t apic_arb_prio;
> int mp_state;
> - int sipi_vector;
> u64 ia32_misc_enable_msr;
> bool tpr_access_reporting;
>
> @@ -819,6 +818,7 @@ int kvm_emulate_wbinvd(struct kvm_vcpu *vcpu);
>
> void kvm_get_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int
> seg);
> int kvm_load_segment_descriptor(struct kvm_vcpu *vcpu, u16 selector, int
> seg);
> +void kvm_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, unsigned int
> vector);
>
> int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int idt_index,
> int reason, bool has_error_code, u32 error_code);
> @@ -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..a8e9369 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -731,7 +731,11 @@ 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;
> + /* assumes that there are only KVM_APIC_INIT/SIPI */
> + apic->pending_events = (1UL << KVM_APIC_INIT);
> + /* make sure pending_events is visible before sending
> + * the request */
> + smp_wmb();
> kvm_make_request(KVM_REQ_EVENT, vcpu);
> kvm_vcpu_kick(vcpu);
> } else {
> @@ -743,13 +747,13 @@ 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);
Why are APIC_DM_STARTUP / APIC_DM_INIT setting KVM_REQ_EVENT again?
Can't see any direct connection. See below.
> +static inline bool kvm_apic_has_events(struct kvm_vcpu *vcpu)
> +{
> + return vcpu->arch.apic->pending_events;
> +}
vcpu->arch.apic = NULL?
> if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win) {
> + kvm_apic_accept_events(vcpu);
> + if (vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED) {
> + r = 1;
> + goto out;
> + }
> +
A separate request bit makes sense, because nothing in this
(KVM_REQ_EVENT conditional) code sequence handles the work from
APIC_DM_STARTUP / APIC_DM_INIT sites (well, before your patch). See
below.
>
> - 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);
vmx_vcpu_reset overwrites vcpu->srcu_idx if ->vcpu_reset is called from
within srcu section.
Also, this is not part of the hotpath and therefore it could be farther
from vcpu_enter_guest. What about processing a new request bit here?
(KVM_REQ_EVENT <-> apic->pending_events relationship is cloudy).
Also the fact kvm_apic_accept_events() is called from sites is annoying,
why is that necessary again?
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