[PATCH] kvm: ioapic: Introduce arch-specific check for lazy update EOI mechanism

[Suravee Suthikulpanit]

commit f458d039db7e ("kvm: ioapic: Lazy update IOAPIC EOI") introduces
the following regression on Intel VMX APICv.

BUG: stack guard page was hit at 000000008f595917 \
(stack is 00000000bdefe5a4..00000000ae2b06f5)
kernel stack overflow (double-fault): 0000 [#1] SMP NOPTI
RIP: 0010:kvm_set_irq+0x51/0x160 [kvm]
Call Trace:
 irqfd_resampler_ack+0x32/0x90 [kvm]
 kvm_notify_acked_irq+0x62/0xd0 [kvm]
 kvm_ioapic_update_eoi_one.isra.0+0x30/0x120 [kvm]
 ioapic_set_irq+0x20e/0x240 [kvm]
 kvm_ioapic_set_irq+0x5c/0x80 [kvm]
 kvm_set_irq+0xbb/0x160 [kvm]
 ? kvm_hv_set_sint+0x20/0x20 [kvm]
 irqfd_resampler_ack+0x32/0x90 [kvm]
 kvm_notify_acked_irq+0x62/0xd0 [kvm]
 kvm_ioapic_update_eoi_one.isra.0+0x30/0x120 [kvm]
 ioapic_set_irq+0x20e/0x240 [kvm]
 kvm_ioapic_set_irq+0x5c/0x80 [kvm]
 kvm_set_irq+0xbb/0x160 [kvm]
 ? kvm_hv_set_sint+0x20/0x20 [kvm]
....

This is due to the logic always force IOAPIC lazy update EOI mechanism
when APICv is activated, which is only needed by AMD SVM AVIC.

Fixes by introducing struct kvm_arch.use_lazy_eoi variable to specify
whether the architecture needs lazy update EOI support.

Reported-by: borisvk@xxxxxxxxxx
Link: https://www.spinics.net/lists/kvm/msg213512.html
Fixes: f458d039db7e ("kvm: ioapic: Lazy update IOAPIC EOI")
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
---
 arch/x86/include/asm/kvm_host.h | 2 ++
 arch/x86/kvm/ioapic.c           | 5 +++--
 arch/x86/kvm/svm/svm.c          | 8 ++++++++
 3 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 42a2d0d..eedfb15 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -982,6 +982,8 @@ struct kvm_arch {
 
 	struct kvm_pmu_event_filter *pmu_event_filter;
 	struct task_struct *nx_lpage_recovery_thread;
+
+	bool use_lazy_eoi;
 };
 
 struct kvm_vm_stat {
diff --git a/arch/x86/kvm/ioapic.c b/arch/x86/kvm/ioapic.c
index 750ff0b..94567c0 100644
--- a/arch/x86/kvm/ioapic.c
+++ b/arch/x86/kvm/ioapic.c
@@ -228,9 +228,10 @@ static int ioapic_set_irq(struct kvm_ioapic *ioapic, unsigned int irq,
 	 * AMD SVM AVIC accelerate EOI write and do not trap,
 	 * in-kernel IOAPIC will not be able to receive the EOI.
 	 * In this case, we do lazy update of the pending EOI when
-	 * trying to set IOAPIC irq.
+	 * trying to set IOAPIC irq if specified by the archtecture.
 	 */
-	if (kvm_apicv_activated(ioapic->kvm))
+	if (kvm_apicv_activated(ioapic->kvm) &&
+	    ioapic->kvm->arch.use_lazy_eoi)
 		ioapic_lazy_update_eoi(ioapic, irq);
 
 	/*
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 2f379ba..b560319 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3882,8 +3882,16 @@ static int svm_vm_init(struct kvm *kvm)
 {
 	if (avic) {
 		int ret = avic_vm_init(kvm);
+
 		if (ret)
 			return ret;
+		/*
+		 * AMD SVM AVIC accelerate EOI write and do not trap,
+		 * in-kernel IOAPIC will not be able to receive the EOI.
+		 * Therefore, specify lazy update of the pending EOI for IOAPIC.
+		 * (Please see in arch/x86/kvm/ioapic.c: ioapic_set_irq().)
+		 */
+		kvm->arch.use_lazy_eoi = true;
 	}
 
 	kvm_apicv_init(kvm, avic);
-- 
1.8.3.1