[bug report] KVM: x86: Do not block APIC write for non ICR registers

[Dan Carpenter <dan.carpenter@xxxxxxxxxx>]

Hello Suravee Suthikulpanit,

The patch 1bd9dfec9fd4: "KVM: x86: Do not block APIC write for non
ICR registers" from Jul 25, 2022, leads to the following Smatch
static checker warning:

	arch/x86/kvm/lapic.c:2302 kvm_apic_write_nodecode()
	error: uninitialized symbol 'val'.

arch/x86/kvm/lapic.c
  2282  void kvm_apic_write_nodecode(struct kvm_vcpu *vcpu, u32 offset)
  2283  {
  2284          struct kvm_lapic *apic = vcpu->arch.apic;
  2285          u64 val;
  2286  
  2287          if (apic_x2apic_mode(apic))
  2288                  kvm_lapic_msr_read(apic, offset, &val);

Originally, this was only called when "offset == APIC_ICR", but the
patch removed that condition.  Now, if kvm_lapic_msr_read() returns 1
then "val" isn't initialized.

  2289          else
  2290                  val = kvm_lapic_get_reg(apic, offset);
  2291  
  2292          /*
  2293           * ICR is a single 64-bit register when x2APIC is enabled.  For legacy
  2294           * xAPIC, ICR writes need to go down the common (slightly slower) path
  2295           * to get the upper half from ICR2.
  2296           */
  2297          if (apic_x2apic_mode(apic) && offset == APIC_ICR) {
  2298                  kvm_apic_send_ipi(apic, (u32)val, (u32)(val >> 32));
  2299                  trace_kvm_apic_write(APIC_ICR, val);
  2300          } else {
  2301                  /* TODO: optimize to just emulate side effect w/o one more write */
  2302                  kvm_lapic_reg_write(apic, offset, (u32)val);

The warning here is for when apic_x2apic_mode() is true but
"offset != APIC_ICR" and kvm_lapic_msr_read() returns 1.

  2303          }
  2304  }

regards,
dan carpenter