kvm: x86: Add support for dynamic APICv activation

Certain runtime conditions require APICv to be temporary deactivated
during runtime.  The current implementation only support run-time
deactivation of APICv when Hyper-V SynIC is enabled, which is not
temporary.

In addition, for AMD, when APICv is (de)activated at runtime,
all vcpus in the VM have to operate in the same mode.  Thus the
requesting vcpu must notify the others.

So, introduce the following:
 * A new KVM_REQ_APICV_UPDATE request bit
 * Interfaces to request all vcpus to update APICv status
 * A new interface to update APICV-related parameters for each vcpu

Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -78,6 +78,8 @@
 #define KVM_REQ_HV_STIMER		KVM_ARCH_REQ(22)
 #define KVM_REQ_LOAD_EOI_EXITMAP	KVM_ARCH_REQ(23)
 #define KVM_REQ_GET_VMCS12_PAGES	KVM_ARCH_REQ(24)
+#define KVM_REQ_APICV_UPDATE \
+	KVM_ARCH_REQ_FLAGS(25, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
 
 #define CR0_RESERVED_BITS                                               \
 	(~(unsigned long)(X86_CR0_PE | X86_CR0_MP | X86_CR0_EM | X86_CR0_TS \
@@ -1482,6 +1484,9 @@ gpa_t kvm_mmu_gva_to_gpa_system(struct kvm_vcpu *vcpu, gva_t gva,
 void kvm_vcpu_deactivate_apicv(struct kvm_vcpu *vcpu);
 bool kvm_apicv_activated(struct kvm *kvm);
 void kvm_apicv_init(struct kvm *kvm, bool enable);
+void kvm_vcpu_update_apicv(struct kvm_vcpu *vcpu);
+void kvm_request_apicv_update(struct kvm *kvm, bool activate,
+			      unsigned long bit);
 
 int kvm_emulate_hypercall(struct kvm_vcpu *vcpu);
 

arch/x86/kvm/x86.c

@@ -26,6 +26,7 @@
 #include "cpuid.h"
 #include "pmu.h"
 #include "hyperv.h"
+#include "lapic.h"
 
 #include <linux/clocksource.h>
 #include <linux/interrupt.h>
@@ -8013,6 +8014,40 @@ void kvm_make_scan_ioapic_request(struct kvm *kvm)
 	kvm_make_all_cpus_request(kvm, KVM_REQ_SCAN_IOAPIC);
 }
 
+void kvm_vcpu_update_apicv(struct kvm_vcpu *vcpu)
+{
+	if (!lapic_in_kernel(vcpu))
+		return;
+
+	vcpu->arch.apicv_active = kvm_apicv_activated(vcpu->kvm);
+	kvm_apic_update_apicv(vcpu);
+	kvm_x86_ops->refresh_apicv_exec_ctrl(vcpu);
+}
+EXPORT_SYMBOL_GPL(kvm_vcpu_update_apicv);
+
+/*
+ * NOTE: Do not hold any lock prior to calling this.
+ *
+ * In particular, kvm_request_apicv_update() expects kvm->srcu not to be
+ * locked, because it calls __x86_set_memory_region() which does
+ * synchronize_srcu(&kvm->srcu).
+ */
+void kvm_request_apicv_update(struct kvm *kvm, bool activate, ulong bit)
+{
+	if (activate) {
+		if (!test_and_clear_bit(bit, &kvm->arch.apicv_inhibit_reasons) ||
+		    !kvm_apicv_activated(kvm))
+			return;
+	} else {
+		if (test_and_set_bit(bit, &kvm->arch.apicv_inhibit_reasons) ||
+		    kvm_apicv_activated(kvm))
+			return;
+	}
+
+	kvm_make_all_cpus_request(kvm, KVM_REQ_APICV_UPDATE);
+}
+EXPORT_SYMBOL_GPL(kvm_request_apicv_update);
+
 static void vcpu_scan_ioapic(struct kvm_vcpu *vcpu)
 {
 	if (!kvm_apic_present(vcpu))
@@ -8203,6 +8238,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 		 */
 		if (kvm_check_request(KVM_REQ_HV_STIMER, vcpu))
 			kvm_hv_process_stimers(vcpu);
+		if (kvm_check_request(KVM_REQ_APICV_UPDATE, vcpu))
+			kvm_vcpu_update_apicv(vcpu);
 	}
 
 	if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win) {