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KVM: VMX: Dont' send posted IRQ if vCPU == this vCPU and vCPU is IN_GUEST_MODE

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When delivering a virtual interrupt, don't actually send a posted interrupt
if the target vCPU is also the currently running vCPU and is IN_GUEST_MODE,
in which case the interrupt is being sent from a VM-Exit fastpath and the
core run loop in vcpu_enter_guest() will manually move the interrupt from
the PIR to vmcs.GUEST_RVI.  IRQs are disabled while IN_GUEST_MODE, thus
there's no possibility of the virtual interrupt being sent from anything
other than KVM, i.e. KVM won't suppress a wake event from an IRQ handler
(see commit fdba608f15, "KVM: VMX: Wake vCPU when delivering posted IRQ
even if vCPU == this vCPU").

Eliding the posted interrupt restores the performance provided by the
combination of commits 379a3c8ee4 ("KVM: VMX: Optimize posted-interrupt
delivery for timer fastpath") and 26efe2fd92 ("KVM: VMX: Handle
preemption timer fastpath").

Thanks Sean for better comments.

Suggested-by: Chao Gao <chao.gao@intel.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Message-Id: <1643111979-36447-1-git-send-email-wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Wanpeng Li
2022-01-25 03:59:39 -08:00
committed by Paolo Bonzini
parent 23e5092b6e
commit 9b44423bf4
1 changed files with 21 additions and 19 deletions
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40
arch/x86/kvm/vmx/vmx.c
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@@ -3937,31 +3937,33 @@ static inline void kvm_vcpu_trigger_posted_interrupt(struct kvm_vcpu *vcpu,
#ifdef CONFIG_SMP
if (vcpu->mode == IN_GUEST_MODE) {
/*
* The vector of interrupt to be delivered to vcpu had
* been set in PIR before this function.
* The vector of the virtual has already been set in the PIR.
* Send a notification event to deliver the virtual interrupt
* unless the vCPU is the currently running vCPU, i.e. the
* event is being sent from a fastpath VM-Exit handler, in
* which case the PIR will be synced to the vIRR before
* re-entering the guest.
*
* Following cases will be reached in this block, and
* we always send a notification event in all cases as
* explained below.
* When the target is not the running vCPU, the following
* possibilities emerge:
*
* Case 1: vcpu keeps in non-root mode. Sending a
* notification event posts the interrupt to vcpu.
* Case 1: vCPU stays in non-root mode. Sending a notification
* event posts the interrupt to the vCPU.
*
* Case 2: vcpu exits to root mode and is still
* runnable. PIR will be synced to vIRR before the
* next vcpu entry. Sending a notification event in
* this case has no effect, as vcpu is not in root
* mode.
* Case 2: vCPU exits to root mode and is still runnable. The
* PIR will be synced to the vIRR before re-entering the guest.
* Sending a notification event is ok as the host IRQ handler
* will ignore the spurious event.
*
* Case 3: vcpu exits to root mode and is blocked.
* vcpu_block() has already synced PIR to vIRR and
* never blocks vcpu if vIRR is not cleared. Therefore,
* a blocked vcpu here does not wait for any requested
* interrupts in PIR, and sending a notification event
* which has no effect is safe here.
* Case 3: vCPU exits to root mode and is blocked. vcpu_block()
* has already synced PIR to vIRR and never blocks the vCPU if
* the vIRR is not empty. Therefore, a blocked vCPU here does
* not wait for any requested interrupts in PIR, and sending a
* notification event also results in a benign, spurious event.
*/
apic->send_IPI_mask(get_cpu_mask(vcpu->cpu), pi_vec);
if (vcpu != kvm_get_running_vcpu())
apic->send_IPI_mask(get_cpu_mask(vcpu->cpu), pi_vec);
return;
}
#endif