KVM: PIT: control word is write-only

Marcelo Tosatti
2010-01-29T19:29:03Z

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 caad189..6a74246 100644
--- 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);