KVM: nVMX: Fix using __this_cpu_read() in preemptible context

 BUG: using __this_cpu_read() in preemptible [00000000] code: qemu-system-x86/4590
  caller is nested_vmx_enter_non_root_mode+0xebd/0x1790 [kvm_intel]
  CPU: 4 PID: 4590 Comm: qemu-system-x86 Tainted: G           OE     5.1.0-rc4+ #1
  Call Trace:
   dump_stack+0x67/0x95
   __this_cpu_preempt_check+0xd2/0xe0
   nested_vmx_enter_non_root_mode+0xebd/0x1790 [kvm_intel]
   nested_vmx_run+0xda/0x2b0 [kvm_intel]
   handle_vmlaunch+0x13/0x20 [kvm_intel]
   vmx_handle_exit+0xbd/0x660 [kvm_intel]
   kvm_arch_vcpu_ioctl_run+0xa2c/0x1e50 [kvm]
   kvm_vcpu_ioctl+0x3ad/0x6d0 [kvm]
   do_vfs_ioctl+0xa5/0x6e0
   ksys_ioctl+0x6d/0x80
   __x64_sys_ioctl+0x1a/0x20
   do_syscall_64+0x6f/0x6c0
   entry_SYSCALL_64_after_hwframe+0x49/0xbe

Accessing per-cpu variable should disable preemption, this patch extends the
preemption disable region for __this_cpu_read().

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Fixes: 52017608 ("KVM: nVMX: add option to perform early consistency checks via H/W")
Cc: stable@vger.kernel.org
Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/nested.c

@@ -2784,14 +2784,13 @@ static int nested_vmx_check_vmentry_hw(struct kvm_vcpu *vcpu)
 	      : "cc", "memory"
 	);
 
-	preempt_enable();
-
 	if (vmx->msr_autoload.host.nr)
 		vmcs_write32(VM_EXIT_MSR_LOAD_COUNT, vmx->msr_autoload.host.nr);
 	if (vmx->msr_autoload.guest.nr)
 		vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, vmx->msr_autoload.guest.nr);
 
 	if (vm_fail) {
+		preempt_enable();
 		WARN_ON_ONCE(vmcs_read32(VM_INSTRUCTION_ERROR) !=
 			     VMXERR_ENTRY_INVALID_CONTROL_FIELD);
 		return 1;
@@ -2803,6 +2802,7 @@ static int nested_vmx_check_vmentry_hw(struct kvm_vcpu *vcpu)
 	local_irq_enable();
 	if (hw_breakpoint_active())
 		set_debugreg(__this_cpu_read(cpu_dr7), 7);
+	preempt_enable();
 
 	/*
 	 * A non-failing VMEntry means we somehow entered guest mode with