On Tue, Dec 08 2020 at 15:11, Marcelo Tosatti wrote:
On Tue, Dec 08, 2020 at 05:02:07PM +0100, Thomas Gleixner wrote:
On Tue, Dec 08 2020 at 16:50, Maxim Levitsky wrote:
On Mon, 2020-12-07 at 20:29 -0300, Marcelo Tosatti wrote:
+This ioctl allows to reconstruct the guest's IA32_TSC and TSC_ADJUST value +from the state obtained in the past by KVM_GET_TSC_STATE on the same vCPU.
+If 'KVM_TSC_STATE_TIMESTAMP_VALID' is set in flags, +KVM will adjust the guest TSC value by the time that passed since the moment +CLOCK_REALTIME timestamp was saved in the struct and current value of +CLOCK_REALTIME, and set the guest's TSC to the new value.
This introduces the wraparound bug in Linux timekeeping, doesnt it?
Which bug?
max_cycles overflow. Sent a message to Maxim describing it.
Truly helpful. Why the hell did you not talk to me when you ran into that the first time?
For one I have no idea which bug you are talking about and if the bug is caused by the VMM then why would you "fix" it in the guest kernel.
- Stop guest, save TSC value of cpu-0 = V.
- Wait for some amount of time = W.
- Start guest, load TSC value with V+W.
Can cause an overflow on Linux timekeeping.
Yes, because you violate the basic assumption which Linux timekeeping makes. See the other mail in this thread.
Thanks,
tglx