KVM: PIT: control word is write-only

PIT control word (address 0x43) is write-only, reads are undefined.

Cc: stable@kernel.org
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index 296aba49472ae3cdcf7580bc79d60d83ed48ce3e..15578f180e596bee481f10451ec375b6ceb37f26 100644 (file)
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -467,6 +467,9 @@ static int pit_ioport_read(struct kvm_io_device *this,
                return -EOPNOTSUPP;
 
        addr &= KVM_PIT_CHANNEL_MASK;
+       if (addr == 3)
+               return 0;
+
        s = &pit_state->channels[addr];
 
        mutex_lock(&pit_state->lock);