macOS can be quite aggressive when it comes to force apps to take long naps for power saving reasons. In addition to this, CNTVCT_EL0 doesn't increase during these naps, meaning the guest is not aware that's missing ticks.
Both things combined mean that guests that run for long enough will suffer from clock skews.
To address this, we introduce here a simple and lightweight host to guest time sync. From the host side, the VMM will send DGRAM packets via vsock with the current time at regular intervals (60 seconds) and when an oversleep (host thread sleeping 3 times more than expected) is detected. On the guest side, "init" spawns a process that listens for such packets and sets the system clock if a delta bigger than 100ms is detected.
slp
commented
1 year ago
macOS can be quite aggressive when it comes to force apps to take long naps for power saving reasons. In addition to this, CNTVCT_EL0 doesn't increase during these naps, meaning the guest is not aware that's missing ticks.
Both things combined mean that guests that run for long enough will suffer from clock skews.
To address this, we introduce here a simple and lightweight host to guest time sync. From the host side, the VMM will send DGRAM packets via vsock with the current time at regular intervals (60 seconds) and when an oversleep (host thread sleeping 3 times more than expected) is detected. On the guest side, "init" spawns a process that listens for such packets and sets the system clock if a delta bigger than 100ms is detected.
Fixes: #80