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Subject[PATCH 4/4] KVM: Add a comment explaining the directed yield pending interrupt logic
From
Add a comment to explain why KVM treats vCPUs with pending interrupts as
in-kernel when a vCPU wants to yield to a vCPU that was preempted while
running in kernel mode.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
virt/kvm/kvm_main.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 6326852bfb3d..4a9e7513c585 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4089,6 +4089,13 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me, bool yield_to_kernel_mode)
continue;
if (kvm_vcpu_is_blocking(vcpu) && !vcpu_dy_runnable(vcpu))
continue;
+
+ /*
+ * Treat the target vCPU as being in-kernel if it has a
+ * pending interrupt, as the vCPU trying to yield may
+ * be spinning waiting on IPI delivery, i.e. the target
+ * vCPU is in-kernel for the purposes of directed yield.
+ */
if (READ_ONCE(vcpu->preempted) && yield_to_kernel_mode &&
!kvm_arch_dy_has_pending_interrupt(vcpu) &&
!kvm_arch_vcpu_preempted_in_kernel(vcpu))
--
2.43.0.472.g3155946c3a-goog

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