[PATCH v2 3/3] KVM: x86: Add a module param to control and enumerate device posted IRQs

Sean Christopherson
2025-03-20T14:20:30Z

Add a module param to allow disabling device posted interrupts without
having to sacrifice all of APICv/AVIC, and to also effectively enumerate
to userspace whether or not KVM may be utilizing device posted IRQs.
Disabling device posted interrupts is very desirable for testing, and can
even be desirable for production environments, e.g. if the host kernel
wants to interpose on device interrupts.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/x86.c | 9 ++++++++-
2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index d881e7d276b1..bf11c5ee50cb 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1922,6 +1922,7 @@ struct kvm_arch_async_pf {
extern u32 __read_mostly kvm_nr_uret_msrs;
extern bool __read_mostly allow_smaller_maxphyaddr;
extern bool __read_mostly enable_apicv;
+extern bool __read_mostly enable_device_posted_irqs;
extern struct kvm_x86_ops kvm_x86_ops;

#define kvm_x86_call(func) static_call(kvm_x86_##func)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f76d655dc9a8..e7eb2198db26 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -227,6 +227,10 @@ EXPORT_SYMBOL_GPL(allow_smaller_maxphyaddr);
bool __read_mostly enable_apicv = true;
EXPORT_SYMBOL_GPL(enable_apicv);

+bool __read_mostly enable_device_posted_irqs = true;
+module_param(enable_device_posted_irqs, bool, 0444);
+EXPORT_SYMBOL_GPL(enable_device_posted_irqs);
+
const struct _kvm_stats_desc kvm_vm_stats_desc[] = {
KVM_GENERIC_VM_STATS(),
STATS_DESC_COUNTER(VM, mmu_shadow_zapped),
@@ -9772,6 +9776,9 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
if (r != 0)
goto out_mmu_exit;

+ enable_device_posted_irqs &= enable_apicv &&
+ irq_remapping_cap(IRQ_POSTING_CAP);
+
kvm_ops_update(ops);

for_each_online_cpu(cpu) {
@@ -13552,7 +13559,7 @@ EXPORT_SYMBOL_GPL(kvm_arch_has_noncoherent_dma);

bool kvm_arch_has_irq_bypass(void)
{
- return enable_apicv && irq_remapping_cap(IRQ_POSTING_CAP);
+ return enable_device_posted_irqs;
}
EXPORT_SYMBOL_GPL(kvm_arch_has_irq_bypass);

--
2.49.0.395.g12beb8f557-goog