KVM: nVMX: Do not load EOI-exitmap while running L2

When L1 IOAPIC redirection-table is written, a request of
KVM_REQ_SCAN_IOAPIC is set on all vCPUs. This is done such that
all vCPUs will now recalc their IOAPIC handled vectors and load
it to their EOI-exitmap.

However, it could be that one of the vCPUs is currently running
L2. In this case, load_eoi_exitmap() will be called which would
write to vmcs02->eoi_exit_bitmap, which is wrong because
vmcs02->eoi_exit_bitmap should always be equal to
vmcs12->eoi_exit_bitmap. Furthermore, at this point
KVM_REQ_SCAN_IOAPIC was already consumed and therefore we will
never update vmcs01->eoi_exit_bitmap. This could lead to remote_irr
of some IOAPIC level-triggered entry to remain set forever.

Fix this issue by delaying the load of EOI-exitmap to when vCPU
is running L1.

One may wonder why not just delay entire KVM_REQ_SCAN_IOAPIC
processing to when vCPU is running L1. This is done in order to handle
correctly the case where LAPIC & IO-APIC of L1 is pass-throughed into
L2. In this case, vmcs12->virtual_interrupt_delivery should be 0. In
current nVMX implementation, that results in
vmcs02->virtual_interrupt_delivery to also be 0. Thus,
vmcs02->eoi_exit_bitmap is not used. Therefore, every L2 EOI cause
a #VMExit into L0 (either on MSR_WRITE to x2APIC MSR or
APIC_ACCESS/APIC_WRITE/EPT_MISCONFIG to APIC MMIO page).
In order for such L2 EOI to be broadcasted, if needed, from LAPIC
to IO-APIC, vcpu->arch.ioapic_handled_vectors must be updated
while L2 is running. Therefore, patch makes sure to delay only the
loading of EOI-exitmap but not the update of
vcpu->arch.ioapic_handled_vectors.

Reviewed-by: Arbel Moshe <arbel.moshe@oracle.com>
Reviewed-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Signed-off-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -73,6 +73,7 @@
 #define KVM_REQ_HV_RESET		KVM_ARCH_REQ(20)
 #define KVM_REQ_HV_EXIT			KVM_ARCH_REQ(21)
 #define KVM_REQ_HV_STIMER		KVM_ARCH_REQ(22)
+#define KVM_REQ_LOAD_EOI_EXITMAP	KVM_ARCH_REQ(23)
 
 #define CR0_RESERVED_BITS                                               \
 	(~(unsigned long)(X86_CR0_PE | X86_CR0_MP | X86_CR0_EM | X86_CR0_TS \
@@ -498,6 +499,7 @@ struct kvm_vcpu_arch {
 	u64 apic_base;
 	struct kvm_lapic *apic;    /* kernel irqchip context */
 	bool apicv_active;
+	bool load_eoi_exitmap_pending;
 	DECLARE_BITMAP(ioapic_handled_vectors, 256);
 	unsigned long apic_attention;
 	int32_t apic_arb_prio;

arch/x86/kvm/kvm_cache_regs.h

@@ -93,6 +93,11 @@ static inline void enter_guest_mode(struct kvm_vcpu *vcpu)
 static inline void leave_guest_mode(struct kvm_vcpu *vcpu)
 {
 	vcpu->arch.hflags &= ~HF_GUEST_MASK;
+
+	if (vcpu->arch.load_eoi_exitmap_pending) {
+		vcpu->arch.load_eoi_exitmap_pending = false;
+		kvm_make_request(KVM_REQ_LOAD_EOI_EXITMAP, vcpu);
+	}
 }
 
 static inline bool is_guest_mode(struct kvm_vcpu *vcpu)

arch/x86/kvm/x86.c

@@ -7110,8 +7110,6 @@ void kvm_make_scan_ioapic_request(struct kvm *kvm)
 
 static void vcpu_scan_ioapic(struct kvm_vcpu *vcpu)
 {
-	u64 eoi_exit_bitmap[4];
-
 	if (!kvm_apic_hw_enabled(vcpu->arch.apic))
 		return;
 
@@ -7124,6 +7122,20 @@ static void vcpu_scan_ioapic(struct kvm_vcpu *vcpu)
 			kvm_x86_ops->sync_pir_to_irr(vcpu);
 		kvm_ioapic_scan_entry(vcpu, vcpu->arch.ioapic_handled_vectors);
 	}
+
+	if (is_guest_mode(vcpu))
+		vcpu->arch.load_eoi_exitmap_pending = true;
+	else
+		kvm_make_request(KVM_REQ_LOAD_EOI_EXITMAP, vcpu);
+}
+
+static void vcpu_load_eoi_exitmap(struct kvm_vcpu *vcpu)
+{
+	u64 eoi_exit_bitmap[4];
+
+	if (!kvm_apic_hw_enabled(vcpu->arch.apic))
+		return;
+
 	bitmap_or((ulong *)eoi_exit_bitmap, vcpu->arch.ioapic_handled_vectors,
 		  vcpu_to_synic(vcpu)->vec_bitmap, 256);
 	kvm_x86_ops->load_eoi_exitmap(vcpu, eoi_exit_bitmap);
@@ -7238,6 +7250,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 		}
 		if (kvm_check_request(KVM_REQ_SCAN_IOAPIC, vcpu))
 			vcpu_scan_ioapic(vcpu);
+		if (kvm_check_request(KVM_REQ_LOAD_EOI_EXITMAP, vcpu))
+			vcpu_load_eoi_exitmap(vcpu);
 		if (kvm_check_request(KVM_REQ_APIC_PAGE_RELOAD, vcpu))
 			kvm_vcpu_reload_apic_access_page(vcpu);
 		if (kvm_check_request(KVM_REQ_HV_CRASH, vcpu)) {