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vmm: cpu: Ensure guest eject is for expected vCPU

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CPU unplug requires co-operation between the guest and the VMM. Ensure
that the CPU the guest marks for eject is the one the VMM expects to be
removed. If the guest were to remove a different vCPU there would be
unexpected behaviour. Further ensure that the boot vCPU is never
unplugged.

Signed-off-by: Rob Bradford <rbradford@meta.com>
This commit is contained in:
Rob Bradford
2026-07-20 16:48:02 +01:00
parent 061b2cda60
commit 3cd8abcd8c
1 changed files with 18 additions and 5 deletions
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23
vmm/src/cpu.rs
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@@ -3384,6 +3384,8 @@ impl BusDevice for AcpiCpuHotplugController {
// lock for the entire function doesn't cause any deadlock.
let mut vcpu_states = self.vcpu_states.lock().unwrap();
let state = &mut vcpu_states[usize::try_from(self.selected_cpu).unwrap()];
// Save before the removal ack below clears it.
let removal_requested = state.removing;
// The ACPI code writes back a 1 to acknowledge the insertion
if (data[0] & (1 << Self::CPU_INSERTING_FLAG) == 1 << Self::CPU_INSERTING_FLAG)
&& state.inserting
@@ -3396,11 +3398,22 @@ impl BusDevice for AcpiCpuHotplugController {
{
state.removing = false;
}
// Trigger removal of vCPU:
if data[0] & (1 << Self::CPU_EJECT_FLAG) == 1 << Self::CPU_EJECT_FLAG
&& let Err(e) = Self::remove_vcpu(self.selected_cpu, state)
{
error!("Error removing vCPU: {e:?}");
// Only allow the guest to eject vCPUs we expect to be ejected (also deny boot
// vcpu).
if data[0] & (1 << Self::CPU_EJECT_FLAG) == 1 << Self::CPU_EJECT_FLAG {
if self.selected_cpu == 0 {
warn!("Ignoring guest request to eject the boot vCPU (CPU 0)");
} else if removal_requested {
if let Err(e) = Self::remove_vcpu(self.selected_cpu, state) {
error!("Error removing vCPU: {e:?}");
}
} else {
warn!(
"Ignoring guest request to eject vCPU {} not marked for \
removal by the VMM",
self.selected_cpu
);
}
}
} else {
warn!("Out of range vCPU id: {}", self.selected_cpu);