[PATCH v2 1/3] KVM: VMX: Consider PID.PIR to determine if vCPU has pending interrupts

[Joao Martins]

Commit 17e433b54393 ("KVM: Fix leak vCPU's VMCS value into other pCPU")
introduced vmx_dy_apicv_has_pending_interrupt() in order to determine
if a vCPU have a pending posted interrupt. This routine is used by
kvm_vcpu_on_spin() when searching for a a new runnable vCPU to schedule
on pCPU instead of a vCPU doing busy loop.

vmx_dy_apicv_has_pending_interrupt() determines if a
vCPU has a pending posted interrupt solely based on PID.ON. However,
when a vCPU is preempted, vmx_vcpu_pi_put() sets PID.SN which cause
raised posted interrupts to only set bit in PID.PIR without setting
PID.ON (and without sending notification vector), as depicted in VT-d
manual section 5.2.3 "Interrupt-Posting Hardware Operation".

Therefore, checking PID.ON is insufficient to determine if a vCPU has
pending posted interrupts and instead we should also check if there is
some bit set on PID.PIR if PID.SN=1.

Fixes: 17e433b54393 ("KVM: Fix leak vCPU's VMCS value into other pCPU")
Reviewed-by: Jagannathan Raman <jag.raman@xxxxxxxxxx>
Co-developed-by: Liran Alon <liran.alon@xxxxxxxxxx>
Signed-off-by: Liran Alon <liran.alon@xxxxxxxxxx>
Signed-off-by: Joao Martins <joao.m.martins@xxxxxxxxxx>
---
v2:
* Fixed broken Sob Chain;
* Add missing tags;
* Only test PID.PIR if PID.SN=1 and reflect that in commit message last
paragraph;
---
 arch/x86/kvm/vmx/vmx.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 31ce6bc2c371..4c7d2935f7ec 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6141,7 +6141,11 @@ static int vmx_sync_pir_to_irr(struct kvm_vcpu *vcpu)
 
 static bool vmx_dy_apicv_has_pending_interrupt(struct kvm_vcpu *vcpu)
 {
-	return pi_test_on(vcpu_to_pi_desc(vcpu));
+	struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
+
+	return pi_test_on(pi_desc) ||
+		(pi_test_sn(pi_desc) &&
+		!bitmap_empty((unsigned long *)pi_desc->pir, NR_VECTORS));
 }
 
 static void vmx_load_eoi_exitmap(struct kvm_vcpu *vcpu, u64 *eoi_exit_bitmap)
-- 
2.11.0