KVM: VMX: Initialize vm86 TSS only once.

Currently vm86 task is initialized on each real mode entry and vcpu
reset. Initialization is done by zeroing TSS and updating relevant
fields. But since all vcpus are using the same TSS there is a race where
one vcpu may use TSS while other vcpu is initializing it, so the vcpu
that uses TSS will see wrong TSS content and will behave incorrectly.
Fix that by initializing TSS only once.
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/vmx.c

@@ -176,7 +176,6 @@ static inline struct vcpu_vmx *to_vmx(struct kvm_vcpu *vcpu)
 	return container_of(vcpu, struct vcpu_vmx, vcpu);
 }
 
-static int init_rmode(struct kvm *kvm);
 static u64 construct_eptp(unsigned long root_hpa);
 static void kvm_cpu_vmxon(u64 addr);
 static void kvm_cpu_vmxoff(void);
@@ -1802,7 +1801,6 @@ static void enter_rmode(struct kvm_vcpu *vcpu)
 
 continue_rmode:
 	kvm_mmu_reset_context(vcpu);
-	init_rmode(vcpu->kvm);
 }
 
 static void vmx_set_efer(struct kvm_vcpu *vcpu, u64 efer)
@@ -2737,22 +2735,6 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx)
 	return 0;
 }
 
-static int init_rmode(struct kvm *kvm)
-{
-	int idx, ret = 0;
-
-	idx = srcu_read_lock(&kvm->srcu);
-	if (!init_rmode_tss(kvm))
-		goto exit;
-	if (!init_rmode_identity_map(kvm))
-		goto exit;
-
-	ret = 1;
-exit:
-	srcu_read_unlock(&kvm->srcu, idx);
-	return ret;
-}
-
 static int vmx_vcpu_reset(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
@@ -2760,10 +2742,6 @@ static int vmx_vcpu_reset(struct kvm_vcpu *vcpu)
 	int ret;
 
 	vcpu->arch.regs_avail = ~((1 << VCPU_REGS_RIP) | (1 << VCPU_REGS_RSP));
-	if (!init_rmode(vmx->vcpu.kvm)) {
-		ret = -ENOMEM;
-		goto out;
-	}
 
 	vmx->rmode.vm86_active = 0;
 
@@ -3009,6 +2987,9 @@ static int vmx_set_tss_addr(struct kvm *kvm, unsigned int addr)
 	if (ret)
 		return ret;
 	kvm->arch.tss_addr = addr;
+	if (!init_rmode_tss(kvm))
+		return  -ENOMEM;
+
 	return 0;
 }
 
@@ -4224,8 +4205,11 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
 		if (!kvm->arch.ept_identity_map_addr)
 			kvm->arch.ept_identity_map_addr =
 				VMX_EPT_IDENTITY_PAGETABLE_ADDR;
+		err = -ENOMEM;
 		if (alloc_identity_pagetable(kvm) != 0)
 			goto free_vmcs;
+		if (!init_rmode_identity_map(kvm))
+			goto free_vmcs;
 	}
 
 	return &vmx->vcpu;