Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall\

Peter Zijlstra
2017-10-02T12:48:19Z

On Mon, Oct 02, 2017 at 02:30:33PM +0200, Paolo Bonzini wrote:
> I don't understand why is it correct to delay interrupt injection just
> because VCPU0 is running in a spinlock-protected region? I just cannot
> see the reason why it's safe and not a recipe for priority inversions.

It is indeed not right. Something like:

raw_spin_lock(&some_lock);

/* do crud */

raw_spin_unlock(&some_lock);

Should not hold off the interrupt that tells you your finger is in
imminent danger of becoming detached. Only when we do
local_irq_disable() (ie. raw_spin_lock_irq*() and the like) should we
avoid interrupt delivery.

This whole fixation on spinlock regions is misguided and must stop, its
wrong on all levels.