vmd(8): fix an interrupt storm in ns8250.

On slower hosts, such as those in a nested virtualization scenario
of OpenBSD guest inside OpenBSD atop Linux KVM, ns8250 can cause a
race between the kevent firing and the vcpu being kicked by an
assert/deassert of the irq.

The end user experiences a "stuck" serial console and the host will
see a vmd process peg the cpu.

This change only toggles the irq if we were in a position of being
ready to receive data on the device so while the kevent might
continuously fire, the vcpu will not be kicked repeatedly.

OK mlarkin@

0 files changed, 0 insertions, 0 deletions