KVM: VMX: Keep list of loaded VMCSs, instead of vcpus

In VMX, before we bring down a CPU we must VMCLEAR all VMCSs loaded on it
because (at least in theory) the processor might not have written all of its
content back to memory. Since a patch from June 26, 2008, this is done using
a per-cpu "vcpus_on_cpu" linked list of vcpus loaded on each CPU.

The problem is that with nested VMX, we no longer have the concept of a
vcpu being loaded on a cpu: A vcpu has multiple VMCSs (one for L1, a pool for
L2s), and each of those may be have been last loaded on a different cpu.

So instead of linking the vcpus, we link the VMCSs, using a new structure
loaded_vmcs. This structure contains the VMCS, and the information pertaining
to its loading on a specific cpu (namely, the cpu number, and whether it
was already launched on this cpu once). In nested we will also use the same
structure to hold L2 VMCSs, and vmx->loaded_vmcs is a pointer to the
currently active VMCS.

Signed-off-by: Nadav Har'El <nyh@il.ibm.com>
Acked-by: Acked-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/vmx.c

@@ -118,6 +118,18 @@ struct vmcs {
 	char data[0];
 };
 
+/*
+ * Track a VMCS that may be loaded on a certain CPU. If it is (cpu!=-1), also
+ * remember whether it was VMLAUNCHed, and maintain a linked list of all VMCSs
+ * loaded on this CPU (so we can clear them if the CPU goes down).
+ */
+struct loaded_vmcs {
+	struct vmcs *vmcs;
+	int cpu;
+	int launched;
+	struct list_head loaded_vmcss_on_cpu_link;
+};
+
 struct shared_msr_entry {
 	unsigned index;
 	u64 data;
@@ -126,9 +138,7 @@ struct shared_msr_entry {
 
 struct vcpu_vmx {
 	struct kvm_vcpu       vcpu;
-	struct list_head      local_vcpus_link;
 	unsigned long         host_rsp;
-	int                   launched;
 	u8                    fail;
 	u8                    cpl;
 	bool                  nmi_known_unmasked;
@@ -142,7 +152,14 @@ struct vcpu_vmx {
 	u64 		      msr_host_kernel_gs_base;
 	u64 		      msr_guest_kernel_gs_base;
 #endif
-	struct vmcs          *vmcs;
+	/*
+	 * loaded_vmcs points to the VMCS currently used in this vcpu. For a
+	 * non-nested (L1) guest, it always points to vmcs01. For a nested
+	 * guest (L2), it points to a different VMCS.
+	 */
+	struct loaded_vmcs    vmcs01;
+	struct loaded_vmcs   *loaded_vmcs;
+	bool                  __launched; /* temporary, used in vmx_vcpu_run */
 	struct msr_autoload {
 		unsigned nr;
 		struct vmx_msr_entry guest[NR_AUTOLOAD_MSRS];
@@ -202,7 +219,11 @@ static int vmx_set_tss_addr(struct kvm *kvm, unsigned int addr);
 
 static DEFINE_PER_CPU(struct vmcs *, vmxarea);
 static DEFINE_PER_CPU(struct vmcs *, current_vmcs);
-static DEFINE_PER_CPU(struct list_head, vcpus_on_cpu);
+/*
+ * We maintain a per-CPU linked-list of VMCS loaded on that CPU. This is needed
+ * when a CPU is brought down, and we need to VMCLEAR all VMCSs loaded on it.
+ */
+static DEFINE_PER_CPU(struct list_head, loaded_vmcss_on_cpu);
 static DEFINE_PER_CPU(struct desc_ptr, host_gdt);
 
 static unsigned long *vmx_io_bitmap_a;
@@ -503,6 +524,13 @@ static void vmcs_clear(struct vmcs *vmcs)
 		       vmcs, phys_addr);
 }
 
+static inline void loaded_vmcs_init(struct loaded_vmcs *loaded_vmcs)
+{
+	vmcs_clear(loaded_vmcs->vmcs);
+	loaded_vmcs->cpu = -1;
+	loaded_vmcs->launched = 0;
+}
+
 static void vmcs_load(struct vmcs *vmcs)
 {
 	u64 phys_addr = __pa(vmcs);
@@ -516,25 +544,24 @@ static void vmcs_load(struct vmcs *vmcs)
 		       vmcs, phys_addr);
 }
 
-static void __vcpu_clear(void *arg)
+static void __loaded_vmcs_clear(void *arg)
 {
-	struct vcpu_vmx *vmx = arg;
+	struct loaded_vmcs *loaded_vmcs = arg;
 	int cpu = raw_smp_processor_id();
 
-	if (vmx->vcpu.cpu == cpu)
-		vmcs_clear(vmx->vmcs);
-	if (per_cpu(current_vmcs, cpu) == vmx->vmcs)
+	if (loaded_vmcs->cpu != cpu)
+		return; /* vcpu migration can race with cpu offline */
+	if (per_cpu(current_vmcs, cpu) == loaded_vmcs->vmcs)
 		per_cpu(current_vmcs, cpu) = NULL;
-	list_del(&vmx->local_vcpus_link);
-	vmx->vcpu.cpu = -1;
-	vmx->launched = 0;
+	list_del(&loaded_vmcs->loaded_vmcss_on_cpu_link);
+	loaded_vmcs_init(loaded_vmcs);
 }
 
-static void vcpu_clear(struct vcpu_vmx *vmx)
+static void loaded_vmcs_clear(struct loaded_vmcs *loaded_vmcs)
 {
-	if (vmx->vcpu.cpu == -1)
-		return;
-	smp_call_function_single(vmx->vcpu.cpu, __vcpu_clear, vmx, 1);
+	if (loaded_vmcs->cpu != -1)
+		smp_call_function_single(
+			loaded_vmcs->cpu, __loaded_vmcs_clear, loaded_vmcs, 1);
 }
 
 static inline void vpid_sync_vcpu_single(struct vcpu_vmx *vmx)
@@ -973,22 +1000,22 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 
 	if (!vmm_exclusive)
 		kvm_cpu_vmxon(phys_addr);
-	else if (vcpu->cpu != cpu)
-		vcpu_clear(vmx);
+	else if (vmx->loaded_vmcs->cpu != cpu)
+		loaded_vmcs_clear(vmx->loaded_vmcs);
 
-	if (per_cpu(current_vmcs, cpu) != vmx->vmcs) {
-		per_cpu(current_vmcs, cpu) = vmx->vmcs;
-		vmcs_load(vmx->vmcs);
+	if (per_cpu(current_vmcs, cpu) != vmx->loaded_vmcs->vmcs) {
+		per_cpu(current_vmcs, cpu) = vmx->loaded_vmcs->vmcs;
+		vmcs_load(vmx->loaded_vmcs->vmcs);
 	}
 
-	if (vcpu->cpu != cpu) {
+	if (vmx->loaded_vmcs->cpu != cpu) {
 		struct desc_ptr *gdt = &__get_cpu_var(host_gdt);
 		unsigned long sysenter_esp;
 
 		kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
 		local_irq_disable();
-		list_add(&vmx->local_vcpus_link,
-			 &per_cpu(vcpus_on_cpu, cpu));
+		list_add(&vmx->loaded_vmcs->loaded_vmcss_on_cpu_link,
+			 &per_cpu(loaded_vmcss_on_cpu, cpu));
 		local_irq_enable();
 
 		/*
@@ -1000,6 +1027,7 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 
 		rdmsrl(MSR_IA32_SYSENTER_ESP, sysenter_esp);
 		vmcs_writel(HOST_IA32_SYSENTER_ESP, sysenter_esp); /* 22.2.3 */
+		vmx->loaded_vmcs->cpu = cpu;
 	}
 }
 
@@ -1007,7 +1035,8 @@ static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
 {
 	__vmx_load_host_state(to_vmx(vcpu));
 	if (!vmm_exclusive) {
-		__vcpu_clear(to_vmx(vcpu));
+		__loaded_vmcs_clear(to_vmx(vcpu)->loaded_vmcs);
+		vcpu->cpu = -1;
 		kvm_cpu_vmxoff();
 	}
 }
@@ -1471,7 +1500,7 @@ static int hardware_enable(void *garbage)
 	if (read_cr4() & X86_CR4_VMXE)
 		return -EBUSY;
 
-	INIT_LIST_HEAD(&per_cpu(vcpus_on_cpu, cpu));
+	INIT_LIST_HEAD(&per_cpu(loaded_vmcss_on_cpu, cpu));
 	rdmsrl(MSR_IA32_FEATURE_CONTROL, old);
 
 	test_bits = FEATURE_CONTROL_LOCKED;
@@ -1495,14 +1524,14 @@ static int hardware_enable(void *garbage)
 	return 0;
 }
 
-static void vmclear_local_vcpus(void)
+static void vmclear_local_loaded_vmcss(void)
 {
 	int cpu = raw_smp_processor_id();
-	struct vcpu_vmx *vmx, *n;
+	struct loaded_vmcs *v, *n;
 
-	list_for_each_entry_safe(vmx, n, &per_cpu(vcpus_on_cpu, cpu),
-				 local_vcpus_link)
-		__vcpu_clear(vmx);
+	list_for_each_entry_safe(v, n, &per_cpu(loaded_vmcss_on_cpu, cpu),
+				 loaded_vmcss_on_cpu_link)
+		__loaded_vmcs_clear(v);
 }
 
 
@@ -1517,7 +1546,7 @@ static void kvm_cpu_vmxoff(void)
 static void hardware_disable(void *garbage)
 {
 	if (vmm_exclusive) {
-		vmclear_local_vcpus();
+		vmclear_local_loaded_vmcss();
 		kvm_cpu_vmxoff();
 	}
 	write_cr4(read_cr4() & ~X86_CR4_VMXE);
@@ -1698,6 +1727,18 @@ static void free_vmcs(struct vmcs *vmcs)
 	free_pages((unsigned long)vmcs, vmcs_config.order);
 }
 
+/*
+ * Free a VMCS, but before that VMCLEAR it on the CPU where it was last loaded
+ */
+static void free_loaded_vmcs(struct loaded_vmcs *loaded_vmcs)
+{
+	if (!loaded_vmcs->vmcs)
+		return;
+	loaded_vmcs_clear(loaded_vmcs);
+	free_vmcs(loaded_vmcs->vmcs);
+	loaded_vmcs->vmcs = NULL;
+}
+
 static void free_kvm_area(void)
 {
 	int cpu;
@@ -4169,6 +4210,7 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
 	if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
 		vmx_set_interrupt_shadow(vcpu, 0);
 
+	vmx->__launched = vmx->loaded_vmcs->launched;
 	asm(
 		/* Store host registers */
 		"push %%"R"dx; push %%"R"bp;"
@@ -4239,7 +4281,7 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
 		"pop  %%"R"bp; pop  %%"R"dx \n\t"
 		"setbe %c[fail](%0) \n\t"
 	      : : "c"(vmx), "d"((unsigned long)HOST_RSP),
-		[launched]"i"(offsetof(struct vcpu_vmx, launched)),
+		[launched]"i"(offsetof(struct vcpu_vmx, __launched)),
 		[fail]"i"(offsetof(struct vcpu_vmx, fail)),
 		[host_rsp]"i"(offsetof(struct vcpu_vmx, host_rsp)),
 		[rax]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_RAX])),
@@ -4279,7 +4321,7 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
 	vmx->idt_vectoring_info = vmcs_read32(IDT_VECTORING_INFO_FIELD);
 
 	asm("mov %0, %%ds; mov %0, %%es" : : "r"(__USER_DS));
-	vmx->launched = 1;
+	vmx->loaded_vmcs->launched = 1;
 
 	vmx->exit_reason = vmcs_read32(VM_EXIT_REASON);
 
@@ -4291,41 +4333,17 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
 #undef R
 #undef Q
 
-static void vmx_free_vmcs(struct kvm_vcpu *vcpu)
-{
-	struct vcpu_vmx *vmx = to_vmx(vcpu);
-
-	if (vmx->vmcs) {
-		vcpu_clear(vmx);
-		free_vmcs(vmx->vmcs);
-		vmx->vmcs = NULL;
-	}
-}
-
 static void vmx_free_vcpu(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 
 	free_vpid(vmx);
-	vmx_free_vmcs(vcpu);
+	free_loaded_vmcs(vmx->loaded_vmcs);
 	kfree(vmx->guest_msrs);
 	kvm_vcpu_uninit(vcpu);
 	kmem_cache_free(kvm_vcpu_cache, vmx);
 }
 
-static inline void vmcs_init(struct vmcs *vmcs)
-{
-	u64 phys_addr = __pa(per_cpu(vmxarea, raw_smp_processor_id()));
-
-	if (!vmm_exclusive)
-		kvm_cpu_vmxon(phys_addr);
-
-	vmcs_clear(vmcs);
-
-	if (!vmm_exclusive)
-		kvm_cpu_vmxoff();
-}
-
 static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
 {
 	int err;
@@ -4347,11 +4365,15 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
 		goto uninit_vcpu;
 	}
 
-	vmx->vmcs = alloc_vmcs();
-	if (!vmx->vmcs)
+	vmx->loaded_vmcs = &vmx->vmcs01;
+	vmx->loaded_vmcs->vmcs = alloc_vmcs();
+	if (!vmx->loaded_vmcs->vmcs)
 		goto free_msrs;
-
-	vmcs_init(vmx->vmcs);
+	if (!vmm_exclusive)
+		kvm_cpu_vmxon(__pa(per_cpu(vmxarea, raw_smp_processor_id())));
+	loaded_vmcs_init(vmx->loaded_vmcs);
+	if (!vmm_exclusive)
+		kvm_cpu_vmxoff();
 
 	cpu = get_cpu();
 	vmx_vcpu_load(&vmx->vcpu, cpu);
@@ -4380,7 +4402,7 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
 	return &vmx->vcpu;
 
 free_vmcs:
-	free_vmcs(vmx->vmcs);
+	free_vmcs(vmx->loaded_vmcs->vmcs);
 free_msrs:
 	kfree(vmx->guest_msrs);
 uninit_vcpu: