KVM: vmx: fix underflow in TSC deadline calculation

KVM: vmx: fix underflow in TSC deadline calculation

If the TSC deadline timer is programmed really close to the deadline or
even in the past, the computation in vmx_set_hv_timer can underflow and
cause delta_tsc to be set to a huge value.  This generally results
in vmx_set_hv_timer returning -ERANGE, but we can fix it by limiting
delta_tsc to be positive or zero.

Reported-by: Wanpeng Li <wanpeng.li@hotmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Change-Id: I12eea18c3ec648dbf782d7754b7b574d7d6aa92c
upstream-status: backport
Signed-off-by: Yunhong Jiang <yunhong.jiang@linux.intel.com>