KVM: x86: hyper-v: Allocate 'struct kvm_vcpu_hv' dynamically

Hyper-V context is only needed for guests which use Hyper-V emulation in
KVM (e.g. Windows/Hyper-V guests). 'struct kvm_vcpu_hv' is, however, quite
big, it accounts for more than 1/4 of the total 'struct kvm_vcpu_arch'
which is also quite big already. This all looks like a waste.

Allocate 'struct kvm_vcpu_hv' dynamically. This patch does not bring any
(intentional) functional change as we still allocate the context
unconditionally but it paves the way to doing that only when needed.

Signed-off-by: Vitaly Kuznetsov <[e-mail]>
Message-Id: <[e-mail]>
Signed-off-by: Paolo Bonzini <[e-mail]>

arch/x86/include/asm/kvm_host.h

···
 
 /* Hyper-V per vcpu emulation context */
 struct kvm_vcpu_hv {
+	struct kvm_vcpu *vcpu;
 	u32 vp_index;
 	u64 hv_vapic;
 	s64 runtime_offset;
···
 	/* used for guest single stepping over the given code position */
 	unsigned long singlestep_rip;
 
-	struct kvm_vcpu_hv hyperv;
+	struct kvm_vcpu_hv *hyperv;
 	struct kvm_vcpu_xen xen;
 
 	cpumask_var_t wbinvd_dirty_mask;

arch/x86/kvm/hyperv.c

···
 
 	for (i = 0; i < ARRAY_SIZE(hv_vcpu->stimer); i++)
 		stimer_cleanup(&hv_vcpu->stimer[i]);
+
+	kfree(hv_vcpu);
+	vcpu->arch.hyperv = NULL;
 }
 
 bool kvm_hv_assist_page_enabled(struct kvm_vcpu *vcpu)
···
 	stimer_prepare_msg(stimer);
 }
 
-void kvm_hv_vcpu_init(struct kvm_vcpu *vcpu)
+int kvm_hv_vcpu_init(struct kvm_vcpu *vcpu)
 {
-	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
+	struct kvm_vcpu_hv *hv_vcpu;
 	int i;
+
+	hv_vcpu = kzalloc(sizeof(struct kvm_vcpu_hv), GFP_KERNEL_ACCOUNT);
+	if (!hv_vcpu)
+		return -ENOMEM;
+
+	vcpu->arch.hyperv = hv_vcpu;
+	hv_vcpu->vcpu = vcpu;
 
 	synic_init(&hv_vcpu->synic);
 
 	bitmap_zero(hv_vcpu->stimer_pending_bitmap, HV_SYNIC_STIMER_COUNT);
 	for (i = 0; i < ARRAY_SIZE(hv_vcpu->stimer); i++)
 		stimer_init(&hv_vcpu->stimer[i], i);
+
+	return 0;
 }
 
 void kvm_hv_vcpu_postcreate(struct kvm_vcpu *vcpu)

arch/x86/kvm/hyperv.h

···
 
 static inline struct kvm_vcpu_hv *to_hv_vcpu(struct kvm_vcpu *vcpu)
 {
-	return &vcpu->arch.hyperv;
+	return vcpu->arch.hyperv;
 }
 
 static inline struct kvm_vcpu *hv_vcpu_to_vcpu(struct kvm_vcpu_hv *hv_vcpu)
 {
-	struct kvm_vcpu_arch *arch;
-
-	arch = container_of(hv_vcpu, struct kvm_vcpu_arch, hyperv);
-	return container_of(arch, struct kvm_vcpu, arch);
+	return hv_vcpu->vcpu;
 }
 
 static inline struct kvm_vcpu_hv_synic *to_hv_synic(struct kvm_vcpu *vcpu)
 {
-	return &vcpu->arch.hyperv.synic;
+	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
+
+	return &hv_vcpu->synic;
 }
 
 static inline struct kvm_vcpu *hv_synic_to_vcpu(struct kvm_vcpu_hv_synic *synic)
···
 void kvm_hv_synic_send_eoi(struct kvm_vcpu *vcpu, int vector);
 int kvm_hv_activate_synic(struct kvm_vcpu *vcpu, bool dont_zero_synic_pages);
 
-void kvm_hv_vcpu_init(struct kvm_vcpu *vcpu);
+int kvm_hv_vcpu_init(struct kvm_vcpu *vcpu);
 void kvm_hv_vcpu_postcreate(struct kvm_vcpu *vcpu);
 void kvm_hv_vcpu_uninit(struct kvm_vcpu *vcpu);
 

arch/x86/kvm/x86.c

···
 	vcpu->arch.pending_external_vector = -1;
 	vcpu->arch.preempted_in_kernel = false;
 
-	kvm_hv_vcpu_init(vcpu);
+	if (kvm_hv_vcpu_init(vcpu))
+		goto free_guest_fpu;
 
 	r = static_call(kvm_x86_vcpu_create)(vcpu);
 	if (r)
-		goto free_guest_fpu;
+		goto free_hv_vcpu;
 
 	vcpu->arch.arch_capabilities = kvm_get_arch_capabilities();
 	vcpu->arch.msr_platform_info = MSR_PLATFORM_INFO_CPUID_FAULT;
···
 	vcpu_put(vcpu);
 	return 0;
 
+free_hv_vcpu:
+	kvm_hv_vcpu_uninit(vcpu);
 free_guest_fpu:
 	kvm_free_guest_fpu(vcpu);
 free_user_fpu: