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vmm: Workaround double reboot triggered by the kernel

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The kernel does not adhere to the ACPI specification (probably to work
around broken hardware) and rather than busy looping after requesting an
ACPI reset it will attempt to reset by other mechanisms (such as i8042
reset.)

In order to trigger a reset the devices write to an EventFd (called
reset_evt.) This is used by the VMM to identify if a reset is requested
and make the VM reboot. As the reset_evt is part of the VMM and reused
for both the old and new VM it is possible for the newly booted VM to
immediately get reset as there is an old event sitting in the EventFd.

The simplest solution is to "drain" the reset_evt EventFd on reboot to
make sure that there is no spurious events in the EventFd.

Fixes: #783

Signed-off-by: Rob Bradford <robert.bradford@intel.com>
(cherry picked from commit ed1e7817cc9dbe013fbcaf1da201a6a46ea9e39e)
This commit is contained in:
Rob Bradford 2020-02-19 16:10:13 +00:00
parent d89ab632e9
commit 89c25ea00c
1 changed files with 6 additions and 0 deletions
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6
vmm/src/lib.rs
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@ -278,6 +278,12 @@ impl Vmm {
let exit_evt = self.exit_evt.try_clone().map_err(VmError::EventFdClone)?;
let reset_evt = self.reset_evt.try_clone().map_err(VmError::EventFdClone)?;
// The Linux kernel fires off an i8042 reset after doing the ACPI reset so there may be
// an event sitting in the shared reset_evt. Without doing this we get very early reboots
// during the boot process.
if self.reset_evt.read().is_ok() {
warn!("Spurious second reset event received. Ignoring.");
}
self.vm = Some(Vm::new(config, exit_evt, reset_evt)?);
}