Firecracker v1.13.1

Fixed

• #5418: Fixed typo in Swagger definition of MmdsConfig, where the property imds_compat was spelled as imds_comat. This caused auto-generated client to create bad requests.

Firecracker v1.13.0

Added

• #5139: Added support for PVTime. This is used to support steal time on ARM machines.
• #5175: Allow including a custom cpu template directly in the json configuration file passed to --config-file under the cpu_config key.
• #5274: Allow taking diff snapshots even if dirty page tracking is disabled, by using mincore(2) to overapproximate the set of dirty pages. Only works if swap is disabled.
• #5290: Extended MMDS to support the EC2 IMDS-compatible session token headers (i.e. "X-aws-ec2-metadata-token" and "X-aws-ec2-metadata-token-ttl-seconds") alongside the MMDS-specific ones.
• #5290: Added mmds.rx_invalid_token and mmds.rx_no_token metrics to track the number of GET requests that were rejected due to token validation failures in MMDS version 2. These metrics also count requests that would be rejected in MMDS version 2 when MMDS version 1 is configured. They helps users assess readiness for migrating to MMDS version 2.
• #5310: Added an optional imds_compat field (default to false if not provided) to PUT requests to /mmds/config to enforce MMDS to always respond plain text contents in the IMDS format regardless of the Accept header in requests. Users need to regenerate snapshots.
• #5364: Added PCI support in Firecracker. PCI support is optional. Users can enable it passing the --enable-pci flag when launching the Firecracker process. When Firecracker process is launched with PCI support, it will create all VirtIO devices using a PCI VirtIO transport. If not enabled, Firecracker will use the MMIO transport instead.

Changed

• #5165: Changed Firecracker snapshot feature from developer preview to generally available. Incremental snapshots remain in developer preview.
• #5282: Updated jailer to no longer require the executable file name to contain firecracker.
• #5290: Changed MMDS to validate the value of "X-metadata-token-ttl-seconds" header only if it is a PUT request to /latest/api/token, as in EC2 IMDS.
• #5290: Changed MMDS version 1 to support the session oriented method as in version 2, allowing easier migration to version 2. Note that MMDS version 1 accepts a GET request even with no token or an invalid token so that existing workloads continue to work.

Deprecated

• #5274: Deprecated the enable_diff_snapshots parameter of the /snapshot/load API. Use track_dirty_pages instead.

Removed

• #5411: Removed official support for Intel Skylake instances. Firecracker will continue to work on those instances, but we will no longer perform automated testing on them.

Fixed

• #5222: Fixed network and rng devices locking up on hosts with non 4K pages.
• #5226: Fixed MMDS to set Content-Type header correctly (i.e. Content-Type: text/plain for IMDS-formatted or error responses and Content-Type: application/json for JSON-formatted responses).
• #5260: Fixed a bug allowing the block device to starve all other devices when backed by a sufficiently slow drive.
• #4207: Fixed GSI numbering on aarch64 to correctly allow up to 96 devices being attached simultaneously.
• #5290: Fixed MMDS to reject PUT requests containing X-Forwarded-For header regardless of its casing (e.g. x-forwarded-for).
• #5328: Fixed MMDS to set the token TTL header (i.e. "X-metadata-token-ttl-seconds" or "X-aws-ec2-metadata-token-ttl-seconds") in the response to "PUT /latest/api/token", as EC2 IMDS does.

Firecracker v1.12.1

Fixed

• #5277: Fixed a bug allowing the block device to starve all other devices when backed by a sufficiently slow drive.

Firecracker v1.12.0

Added

• #5048: Added support for PVH boot mode. This is used when an x86 kernel provides the appropriate ELF Note to indicate that PVH boot mode is supported. Linux kernels newer than 5.0 compiled with CONFIG_PVH=y set this ELF Note, as do FreeBSD kernels.
• #5065 Added support for Intel AMX (Advanced Matrix Extensions). To be able to take and restore a snapshot of Intel AMX state, Xsave is used instead of kvm_xsave, so users need to regenerate snapshots.
• #4731: Added support for modifying the host TAP device name during snapshot restore.
• #5146: Added Intel Sapphire Rapids as a supported and tested platform for Firecracker.
• #5148: Added ARM Graviton4 as a supported and tested platform for Firecracker.

Changed

• #5118: Cleared WAITPKG CPUID bit in CPUID normalization. The feature enables a guest to put a physical processor into an idle state, which is undesirable in a FaaS environment since that is what the host wants to decide.
• #5142: Clarified what CPU models are supported by each existing CPU template. Firecracker exits with an error if a CPU template is used on an unsupported CPU model.

Deprecated

• #4948: Deprecated the page_size_kib field in the UFFD handshake, and replaced it with a page_size field. The page_size_kib field is misnamed, as the value Firecracker sets it to is actually the page size in bytes, not KiB. It will be removed in Firecracker 2.0.

Fixed

• #5074 Fix the SendCtrlAltDel command not working for ACPI-enabled guest kernels, by dropping the i8042.nopnp argument from the default kernel command line Firecracker constructs.
• #5122: Keep the UFFD Unix domain socket open to prevent the race condition between the guest memory mappings message and the shutdown event that was sometimes causing arrival of an empty message on the UFFD handler side.
• #5143: Fixed to report process_startup_time_us and process_startup_time_cpu_us metrics for api_server right after the API server starts, while previously reported before applying seccomp filter and starting the API server. Users may observe a bit longer startup time metrics.

Firecracker v1.11.0

Added

• #4987: Reset physical counter register (CNTPCT_EL0) on VM startup. This avoids VM reading the host physical counter value. This is only possible on 6.4 and newer kernels. For older kernels physical counter will still be passed to the guest unmodified. See more info here
• #5088: Added AMD Genoa as a supported and tested platform for Firecracker.

Changed

• #4913: Removed unnecessary fields (max_connections and max_pending_resets) from the snapshot format, bumping the snapshot version to 5.0.0. Users need to regenerate snapshots.
• #4926: Replace underlying implementation for seccompiler from in house one in favor of libseccomp which produces smaller and more optimized BPF code.

Fixed

• #4921: Fixed swagger CpuConfig definition to include missing aarch64-specific fields.
• #4916: Fixed IovDeque implementation to work with any host page size. This fixes virtio-net device on non 4K host kernels.
• #4991: Fixed mem_size_mib and track_dirty_pages being mandatory for all PATCH /machine-config requests. Now, they can be omitted which leaves these parts of the machine configuration unchanged.
• #5007: Fixed watchdog softlockup warning on x86_64 guests when a vCPU is paused during GDB debugging.
• #5021 If a balloon device is inflated post UFFD-backed snapshot restore, Firecracker now causes remove UFFD messages to be sent to the UFFD handler. Previously, no such message would be sent.
• #5034: Fix an integer underflow in the jailer when computing the value it passes to Firecracker's --parent-cpu-time-us values, which caused development builds of Firecracker to crash (but production builds were unaffected as underflows do not panic in release mode).
• #5045: Fixed an issue where firecracker intermittently receives SIGHUP when using jailer with --new-pid-ns but without --daemonize.
• #4995: Firecracker no longer overwrites CPUID leaf 0x80000000 when running AMD hardware, meaning the guest can now discover a greater range of CPUID leaves in the extended function range (this range is host kernel dependent).
• #5046: Retry KVM_CREATE_VM on EINTR that occasionally happen on heavily loaded hosts to improve reliability of microVM creation.
• #5052: Build the empty seccomp policy as default for debug builds to avoid crashes on syscalls introduced by debug assertions from Rust 1.80.0.

Firecracker v1.10.1

Changed

• #4907: Bump snapshot version to 4.0.0. Ensure Firecracker v1.10.1 is incompatible with snapshots from other releases.

Firecracker v1.10.0

Added

• #4834: Add VIRTIO_NET_F_RX_MRGBUF support to the virtio-net device. When this feature is negotiated, guest virtio-net driver can perform more efficient memory management which in turn improves RX and TX performance.
• #4460: Add a call to KVM_KVMCLOCK_CTRL after pausing vCPUs on x86_64 architectures. This ioctl sets a flag in the KVM state of the vCPU indicating that it has been paused by the host userspace. In guests that use kvmclock, the soft lockup watchdog checks this flag. If it is set, it won't trigger the lockup condition. Calling the ioctl for guests that don't use kvmclock will fail. These failures are not fatal. We log the failure and increase the vcpu.kvmclock_ctrl_fails metric.
• #4869: Added support for Aarch64 systems which feature CPU caches with a number of sets higher than u16::MAX.
• #4797, #4854: Added GDB debugging support for a microVM guest kernel. Please see our GDB debugging documentation for more information.

Changed

• #4844: Upgrade virtio-net device to use readv syscall to avoid unnecessary memory copies on RX path, increasing the RX performance.

Removed

• #4804: Drop Support for guest kernel 4.14. Linux 4.14 reached end-of-life in January 2024 The minimum supported guest kernel now is 5.10.

Fixed

• #4796: Fixed Vsock not notifying guest about TRANSPORT_RESET_EVENT event after snapshot restore. This resulted in guest waiting indefinitely on a connection which was reset during snapshot creation.
• #4790: v1.9.0 was missing most of the debugging information in the debuginfo file, due to a change in the Cargo defaults. This has been corrected.
• #4826: Add missing configuration of tap offload features when restoring from a snapshot. Setting the features was previously moved from net device creation to device activation time, but it was not reflected in the restore path. This was leading to inability to connect to the restored VM if the offload features were used.

Firecracker v1.9.1

Fixed

• #4824: Add missing configuration of tap offload features when restoring from a snapshot. Setting the features was previously moved from net device creation to device activation time, but it was not reflected in the restore path. This was leading to inability to connect to the restored VM if the offload features were used.
• #4829: v1.9.0 was missing most of the debugging information in the debuginfo file, due to a change in the Cargo defaults. This has been corrected.

Firecracker v1.9.0

Added

• #4687: Added VMGenID support for microVMs running on ARM hosts with 6.1 guest kernels. Support for VMGenID via DeviceTree bindings exists only on mainline 6.10 Linux onwards. Users of Firecracker will need to backport the relevant patches on top of their 6.1 kernels to make use of the feature.
• #4732, #4733, #4741, #4746: Added official support for 6.1 microVM guest kernels.

Changed

Deprecated

• Support for guest kernel 4.14 is now deprecated. We will completely remove 4.14 support with Firecracker version v1.10

Removed

• #4689: Drop support for host kernel 4.14. Linux 4.14 reached end-of-life in January 2024. The minimum supported kernel now is 5.10. Guest kernel 4.14 is still supported.

Fixed

• 4680: Fixed an issue (#4659) where the virtio-net device implementation would always assume the guest accepts all VirtIO features the device offers. This is always true with the Linux guest kernels we are testing but other kernels, like FreeBSD make different assumptions. This PR fixes the emulation code to set the TAP features based on the features accepted by the guest.

Firecracker v1.8.0

Added

• #4428: Added ACPI support to Firecracker for x86_64 microVMs. Currently, we pass ACPI tables with information about the available vCPUs, interrupt controllers, VirtIO and legacy x86 devices to the guest. This allows booting kernels without MPTable support. Please see our kernel policy documentation for more information regarding relevant kernel configurations.
• #4487: Added support for the Virtual Machine Generation Identifier (VMGenID) device on x86_64 platforms. VMGenID is a virtual device that allows VMMs to notify guests when they are resumed from a snapshot. Linux includes VMGenID support since version 5.18. It uses notifications from the device to reseed its internal CSPRNG. Please refer to snapshot support and random for clones documention for more info on VMGenID. VMGenID state is part of the snapshot format of Firecracker. As a result, Firecracker snapshot version is now 2.0.0.

Changed

• #4492: Changed --config parameter of cpu-template-helper optional. Users no longer need to prepare kernel, rootfs and Firecracker configuration files to use cpu-template-helper.
• #4537 Changed T2CL template to pass through bit 27 and 28 of MSR_IA32_ARCH_CAPABILITIES (RFDS_NO and RFDS_CLEAR) since KVM consider they are able to be passed through and T2CL isn't designed for secure snapshot migration between different processors.
• #4537 Changed T2S template to set bit 27 of MSR_IA32_ARCH_CAPABILITIES (RFDS_NO) to 1 since it assumes that the fleet only consists of processors that are not affected by RFDS.
• #4388: Avoid setting kvm_immediate_exit to 1 if are already handling an exit, or if the vCPU is stopped. This avoids a spurious KVM exit upon restoring snapshots.
• #4567: Do not initialize vCPUs in powered-off state upon snapshot restore. No functional change, as vCPU initialization is only relevant for the booted case (where the guest expects CPUs to be powered off).

Deprecated

• Firecracker's --start-time-cpu-us and --start-time-us parameters are deprecated and will be removed in v2.0 or later. They are used by the jailer to pass the value that should be subtracted from the (CPU) time, when emitting the start_time_us and start_time_cpu_us metrics. These parameters were never meant to be used by end customers, and we recommend doing any such time adjustments outside Firecracker.
• Booting with microVM kernels that rely on MPTable on x86_64 is deprecated and support will be removed in v2.0 or later. We suggest to users of Firecracker to use guest kernels with ACPI support. For x86_64 microVMs, ACPI will be the only way Firecracker passes hardware information to the guest once MPTable support is removed.

Fixed

• #4526: Added a check in the network TX path that the size of the network frames the guest passes to us is not bigger than the maximum frame the device expects to handle. On the TX path, we copy frames destined to MMDS from guest memory to Firecracker memory. Without the check, a mis-behaving virtio-net driver could cause an increase in the memory footprint of the Firecracker process. Now, if we receive such a frame, we ignore it and increase Net::tx_malformed_frames metric.
• #4536: Make the first differential snapshot taken after a full snapshot contain only the set of memory pages changed since the full snapshot. Previously, these differential snapshots would contain all memory pages. This will result in potentially much smaller differential snapshots after a full snapshot.
• #4578: Fix UFFD support not being forward-compatible with new ioctl options introduced in Linux 6.6. See also bytecodealliance/userfaultfd-rs#61.
• #4630: On x86_64, when taking a snapshot, if a vCPU has MSR_IA32_TSC_DEADLINE set to 0, Firecracker will replace it with the MSR_IA32_TSC value from the same vCPU. This is to guarantee that the vCPU will continue receiving TSC interrupts after restoring from the snapshot even if an interrupt is lost when taking a snapshot.
• #4666: Fixed Firecracker sometimes restoring MSR_IA32_TSC_DEADLINE before MSR_IA32_TSC. Now it always restores MSR_IA32_TSC_DEADLINE MSR after MSR_IA32_TSC, as KVM relies on the guest TSC for correct restoration of MSR_IA32_TSC_DEADLINE. This fixed guests using the TSC_DEADLINE hardware feature receiving incorrect timer interrupts after snapshot restoration, which could lead to them seemingly getting stuck in sleep-related syscalls (see also #4099).