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feat(memory): support isolated virtio-mem growth on KVM - #4
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ltstriker merged 2 commits intoOct 28, 2026
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Callers using the bundled libkrunfw kernel could not add kernel parameters: krun_start_enter builds the command line from a fixed prolog plus the krun environment. BoxLite needs "maxcpus=N" to boot with every possible vCPU created but only N online, so it can bring more CPUs online later without restarting the VM. Each call appends one validated token. The tokens go into krun_env, which is appended for both the bundled kernel and one set with krun_set_kernel, so the parameter applies either way. Design: boxlite-ai/boxlite#2126 Co-Authored-By: Claude Opus 5.5 <[email protected]>
Expose grow-only memory requests after VM start, reserve inaccessible slots, and report partial allocation. Count the bundled kernel in the initial RAM budget and keep hotplug ranges outside the x86 MMIO gap.
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ltstriker
marked this pull request as ready for review
October 28, 2026 06:58
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TL;DR
Support grow-only RAM hotplug on Linux/KVM while counting the bundled kernel within the configured RAM budget.
Design doc: boxlite-ai/boxlite#2126
Documentation: https://github.com/ltstriker/libkrun/blob/tingliang/box-online-resize/README.md#online-memory-growth-linux-generic-variant
How it works
Add kernel command-line parameters and asynchronous memory request/status APIs. Virtio-mem plugs 2 MiB blocks into 128 MiB KVM slots; unallocated slots stay inaccessible. Preserve partial allocation and keep x86 hotplug outside MMIO.
Dependency of boxlite-ai/boxlite#2138.
Verification
From BoxLite:
make test:unit:libkrun→ passes on x86/KVM. RAM-budget and MMIO regressions fail with fixes reverted and pass when restored. Real VM memory growth passes. ARM remains untested.