[PATCH v2 1/3] KVM: VMX: Don't send UNBLOCK when starting device assignment without APICv

Sean Christopherson
2025-03-20T14:20:26Z

When starting device assignment, i.e. potential IRQ bypass, don't blast
KVM_REQ_UNBLOCK if APICv is disabled/unsupported. There is no need to
wake vCPUs if they can never use VT-d posted IRQs (sending UNBLOCK guards
against races being vCPUs blocking and devices starting IRQ bypass).

Opportunistically use kvm_arch_has_irq_bypass() for all relevant checks in
the VMX Posted Interrupt code so that all checks in KVM x86 incorporate
the same information (once AMD/AVIC is given similar treatment).

Cc: Yosry Ahmed <yosry.ahmed@linux.dev>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/vmx/posted_intr.c | 7 +++----
arch/x86/kvm/x86.c | 1 +
2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/vmx/posted_intr.c b/arch/x86/kvm/vmx/posted_intr.c
index ec08fa3caf43..16121d29dfd9 100644
--- a/arch/x86/kvm/vmx/posted_intr.c
+++ b/arch/x86/kvm/vmx/posted_intr.c
@@ -134,9 +134,8 @@ void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)

static bool vmx_can_use_vtd_pi(struct kvm *kvm)
{
- return irqchip_in_kernel(kvm) && enable_apicv &&
- kvm_arch_has_assigned_device(kvm) &&
- irq_remapping_cap(IRQ_POSTING_CAP);
+ return irqchip_in_kernel(kvm) && kvm_arch_has_irq_bypass() &&
+ kvm_arch_has_assigned_device(kvm);
}

/*
@@ -254,7 +253,7 @@ bool pi_has_pending_interrupt(struct kvm_vcpu *vcpu)
*/
void vmx_pi_start_assignment(struct kvm *kvm)
{
- if (!irq_remapping_cap(IRQ_POSTING_CAP))
+ if (!kvm_arch_has_irq_bypass())
return;

kvm_make_all_cpus_request(kvm, KVM_REQ_UNBLOCK);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 69c20a68a3f0..f76d655dc9a8 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -13554,6 +13554,7 @@ bool kvm_arch_has_irq_bypass(void)
{
return enable_apicv && irq_remapping_cap(IRQ_POSTING_CAP);
}
+EXPORT_SYMBOL_GPL(kvm_arch_has_irq_bypass);

int kvm_arch_irq_bypass_add_producer(struct irq_bypass_consumer *cons,
struct irq_bypass_producer *prod)
--
2.49.0.395.g12beb8f557-goog