On 07/04/20 22:20, Thomas Gleixner wrote: >>> Havind said that, I thought disabling interrupts does not mask exceptions. >>> So page fault exception should have been delivered even with interrupts >>> disabled. Is that correct? May be there was no vm exit/entry during >>> those 10 seconds and that's why. > No. Async PF is not a real exception. It has interrupt semantics and it > can only be injected when the guest has interrupts enabled. It's bad > design. Page-ready async PF has interrupt semantics. Page-not-present async PF however does not have interrupt semantics, it has to be injected immediately or not at all (falling back to host page fault in the latter case). So page-not-present async PF definitely needs to be an exception, this is independent of whether it can be injected when IF=0. Hypervisors do not have any reserved exception vector, and must use vectors up to 31, which is why I believe #PF was used in the first place (though that predates my involvement in KVM by a few years). These days, #VE would be a much better exception to use instead (and it also has a defined mechanism to avoid reentrancy). Paolo
