On Sun, Jun 20, 2021 at 7:34 PM stsp <stsp2@xxxxxxxxx> wrote: > > 19.06.2021 00:07, Jim Mattson пишет: > > I believe DS is illegal. Per the SDM, Checks on Guest Segment Registers: > OK, so this indeed have solved > the biggest part of the problem, > thanks again. > > Now back to the original problem, > where I was getting a page fault > on some CPUs sometimes. > I digged a bit more. > It seems I am getting a race of > this kind: exception in guest happens > at the same time when the host's > SIGALRM arrives. KVM returns to > host with the exception somehow > "pending", but its still on ring3, not > switched to the ring0 handler. > > Then from host I inject the interrupt > (which is what SIGALRM asks for), > and when I enter the guest, it throws > the pending exception instead of > executing the interrupt handler. > I suspect the bug is again on my side, > but I am not sure how to handle that > kind of race. I suppose I need to look > at some interruptibility state to find > out that the interrupt cannot be injected > at that time. But I can't find if KVM > exports the interruptibility state, other > than guest's IF/VIF flag, which is not > enough in this case. Maybe what you want is run->ready_for_interrupt_injection? And, if that's not set, try KVM_RUN with run->request_interrupt_window set? > Also I am a bit puzzled why I can't > see such race on an I7 CPU even > after disabling the unrestricted_guest. > > Any ideas? :) I'm guessing that your core2duo doesn't have a VMX preemption timer, and this has some subtle effect on how the alarm interrupts VMX non-root operation. On the i7, try setting the module parameter preemption_timer to 0.
