firecracker-microvm/firecracker · error

slot range should be valid

Error message

slot range should be valid

What it means

Error "slot range should be valid" thrown in firecracker-microvm/firecracker.

Source

Thrown at src/vmm/src/vstate/memory.rs:635

        Ok(())
    }

    pub(crate) fn slot_cnt(&self) -> u32 {
        u32::try_from(u64_to_usize(self.len()) / self.slot_size).unwrap()
    }

    pub(crate) fn mem_slot(&self, slot: u32) -> GuestMemorySlot<'_> {
        assert!(slot >= self.slot_from && slot < self.slot_from + self.slot_cnt());

        let offset = ((slot - self.slot_from) as u64) * (self.slot_size as u64);

        GuestMemorySlot {
            slot,
            guest_addr: self.start_addr().unchecked_add(offset),
            slice: self
                .inner
                .get_slice(MemoryRegionAddress(offset), self.slot_size)
                .expect("slot range should be valid"),
        }
    }

    /// Returns a snapshot of the slots and their state at the time of calling
    ///
    /// Note: to avoid TOCTOU races use only within VMM thread.
    pub(crate) fn slots(&self) -> impl Iterator<Item = (GuestMemorySlot<'_>, bool)> {
        self.plugged
            .lock()
            .unwrap()
            .iter()
            .enumerate()
            .map(|(i, b)| {
                (
                    self.mem_slot(self.slot_from + u32::try_from(i).unwrap()),
                    *b,
                )
            })

View on GitHub (pinned to 9384f395f5)

Solutions

1. Ensure the memory slot's guest range is valid and backed by the region before registering it with KVM.
2. Check the memory-region construction for overlapping or empty slot ranges.

When it happens

Trigger: Thrown at src/vmm/src/vstate/memory.rs:635 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of firecracker-microvm/firecracker@9384f395f5 (2026-08-19). Data as JSON: /api/errors/7ffcd71c2211d474. Report an issue: GitHub.