KVM: x86: Consider LAPIC TSC-Deadline timer expired if deadline too short
authorLiran Alon <liran.alon@oracle.com>
Tue, 16 Apr 2019 17:36:34 +0000 (20:36 +0300)
committerPaolo Bonzini <pbonzini@redhat.com>
Thu, 18 Apr 2019 16:53:17 +0000 (18:53 +0200)
commitc09d65d9eab69985c75f98ed64541229f6fa9aa6
treec741b2c49a84b863e5c8c27731c9f370a02c4509
parent78671ab4c9f42e2348bff60e2f4a0b3bb62353af
KVM: x86: Consider LAPIC TSC-Deadline timer expired if deadline too short

If guest sets MSR_IA32_TSCDEADLINE to value such that in host
time-domain it's shorter than lapic_timer_advance_ns, we can
reach a case that we call hrtimer_start() with expiration time set at
the past.

Because lapic_timer.timer is init with HRTIMER_MODE_ABS_PINNED, it
is not allowed to run in softirq and therefore will never expire.

To avoid such a scenario, verify that deadline expiration time is set on
host time-domain further than (now + lapic_timer_advance_ns).

A future patch can also consider adding a min_timer_deadline_ns module parameter,
similar to min_timer_period_us to avoid races that amount of ns it takes
to run logic could still call hrtimer_start() with expiration timer set
at the past.

Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
arch/x86/kvm/lapic.c