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Firecracker
Firecracker microVM news
Firecracker advertised a broken ACPI PCI hot-plug path
Firecracker's ACPI tables advertised PCI hot-plug for every root-bus slot. The eject path called a helper device the VMM never published, so a Linux guest with ACPI PCI hot-plug saw broken slot entries under sysfs.
Firecracker now lets guests move a virtio-pci BAR
A guest write that reprogrammed a virtio-pci BAR used to be ignored, so the device stayed at the address Firecracker picked. The mapping and the notify events now follow the new base when the guest turns memory decoding back on.
Firecracker now supports AWS Graviton5
Firecracker lists the host machines it officially runs on. Graviton5 metal is now on that list.
Firecracker ARM CPU templates failed on newer host kernels
Custom ARM CPU templates write chip identity registers. On Linux 6.15 and later those writes failed unless the VMM asked KVM for permission.
Firecracker can skip fsync when it writes a snapshot
Taking a snapshot used to always flush the files to disk. A new create-snapshot option lets you skip that flush.
Firecracker can hang when a log write hits a broken pipe
The API thread can get a broken-pipe signal while writing logs. Logging from that handler, plus a missing resume syscall on the filter, could hang or kill the process.
Firecracker snapshot restore could succeed with a dead PCI device
Firecracker snapshot restore could report success even when a PCI virtio device failed to start again. The guest then had a device that never processed a request.
Firecracker hid eIBRS from guests on newer host kernels
Firecracker used to read the host's speculation-defense bits before telling KVM what the guest CPU looked like. On Linux 6.18 those reads came back empty, so the guest thought eIBRS was off and used the slower retpoline path.
Firecracker could hang if you hot-plugged a device during a guest reset
Adding a PCI device while the guest reset another virtio-pci device could lock the VMM. Two internal locks were taken in opposite order.
Firecracker now tells T2S guests that fill-buffer flush works
T2S is Firecracker's CPU template for Skylake and Cascade Lake. Those guests could miss that a standard flush clears leftover fill-buffer data, and skip a stale-data mitigation.
Firecracker restore can now pick a different huge-page setup
A snapshot remembers how the host backed guest memory. Restore can now keep that setting or choose another page size, instead of matching the original host.
After a pause, Firecracker stopped completing new host connections
After a Firecracker pause and resume, new connections started from the host never completed. Guest-to-host still worked.
Firecracker now rejects a huge memory request
The host control API used to accept a huge memory size and wrap it to zero bytes. Main now rejects that on the way in.