linux: run embedded Firecracker with virtio-pmem#18
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Build Firecracker 1.16.0 with rules_rs for ARM64 and x86_64. Embed Firecracker, the Linux kernel, the initramfs, and the runtime SquashFS in linux-actiond; copy the immutable files to sealed memfds and execute Firecracker with execveat. Keep cas.ext4 as the only persistent file and attach cas.ext4 and the runtime SquashFS as PCI virtio block devices. Proxy REAPI requests through Firecracker's Unix-vsock backend. Add ARM64 and x86_64 release binaries, an x86_64 KVM LLVM smoke comparison against the Linux host, and an ARM64 release build on the GitHub ARM64 runner.
Expose cas.ext4 through PCI virtio-pmem and mount /dev/pmem0 with ext4 DAX. Keep the runtime SquashFS on virtio-blk, validate Firecracker's 2 MiB pmem alignment, and wait for libnvdimm's asynchronous pmem block-device registration. Use nobarrier to retain the existing Unsafe persistence semantics.
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Author: zbarsky-bot
Builds Firecracker 1.16.0 from source with
rules_rs, embeds Firecracker inlinux-actiond, attaches the persistentcas.ext4file as PCIvirtio-pmem, and mounts/dev/pmem0as ext4 withdax=always,nobarrier. The runtime SquashFS remains a PCI virtio block device.vm/linux.configandvm/linux_x86_64.configenable the libnvdimm, PMEM, DAX, memory hotplug, and architecture-specific options required by/dev/pmem0.CONFIG_NVDIMM_PFN=yis required because it selectsCONFIG_ND_CLAIM; withoutCONFIG_ND_CLAIM,devm_namespace_enable()returns-ENXIOand Linux does not create/dev/pmem0.The LLVM
llvm-tblgensmoke executed 1,998 actions in both configurations. PCI virtio-pmem with ext4 DAX measured 289.431s actiond / 274.500s Linux host, while PCI virtio-blk measured 287.837s actiond / 293.087s Linux host. The +1.594s (+0.55%) actiond delta provides no measured PMEM performance improvement; this PR preserves the implementation as an alternative configuration.The Linux x86_64 LLVM smoke, Linux ARM64 build, and release build completed successfully in GitHub Actions run 27480307956 before the remaining Windows smoke was canceled.