On 23/09/2016 11:17, Alexander Graf wrote:

quoted

quoted

On the other hand, what happens if you run new QEMU with old userspace?
With user_timer_pending you'd get an infinite stream of vmexits the
first time the timer fires, wouldn't you?  Whereas if you keep it in the
kernel, userspace would simply not get the interrupt (because it doesn't
know about kernel_timer_pending) and think it got a spurious vmexit.
The kernel's IRQ would stay masked and everything would just (not) work
like before your patch?

Yes, we'd definitely stay more compatible by tracking it only in the
kernel. I'm not fully convinced that it's the better interface, but
since both Christoffer and you seem to choke on that part, I'll give it
a stab ;).

Cool!  FWIW my suggestion for kernel_timer_pending's name would be
timer_irq_level (nicely matching timer->irq.level in the kernel).

Paolo