On 28/11/2016 17:36, Marcelo Tosatti wrote:
> If the source masterclock is disabled, then the guest does
> not enable the optimization to not use a global variable
> to guarantee monotonicity. Therefore there will be no
> time backwards events (the timer backwards events crashed
> guests, and are the reason for reading from guest memory).
>
> So if there are no flaws in the reasoning above,
> no, there is no need to read from memory if
> masterclock is disabled.
Yeah, the reasoning is sound. So you go from what Eduardo and I were
thinking:
if last KVM_GET_CLOCK was not reliable then
read from memory
to this:
if last KVM_GET_CLOCK was not reliable && masterclock is enabled
read from memory
but:
- on an old kernel, the left side is always true and the right side is
unknown (so we must assume it's true and read from memory)
- on a new kernel, the two sides of the "&&" are exactly the opposite,
so the result is always false
and then it becomes
if old kernel then
read from memory
Got it finally. :)
Paolo
> Can you state the reasons why you think it should be enabled?
>
