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4eafe4bbac
Two coordinated changes that together raise the per-sandbox virtio
device cap on x86_64 by ~10x:
1. **Enable msb_krun's userspace split irqchip** in the runtime
(vendor/microsandbox submodule bump). KVM's in-kernel IOAPIC is
hardcoded to 24 pins, of which libkrun's allocator hands out only
IRQs 5..15 — saturated by a typical agent-vm config (rootfs, upper,
runtime fs, network, vsock, console, balloon, rng) plus a couple of
`--mount`s, so an extra mount has historically tripped
`RegisterNetDevice(IrqsExhausted)` at boot. The userspace IOAPIC
exposes 256 pins, lifting the libkrun allocator ceiling to
IRQ_MAX_SPLIT = 223. Requires a libkrun fork (pinned in
Cargo.toml) with three correctness fixes on top of upstream 0.1.13;
without them, enabling split_irqchip crashes the VMM during boot or
silently truncates the kernel cmdline.
2. **Patch libkrunfw to bump x86 COMMAND_LINE_SIZE 2048 → 16384**.
Each virtio_mmio device adds ~36 bytes of cmdline; past ~10 user
mounts the assembled cmdline crosses the stock 2048 cap, the kernel
silently truncates the tail (which includes virtio-console), and
the guest hangs in early boot with `kernel.log` stuck at 0 bytes.
New `libkrunfw-overrides/cmdline-size_x86_64.patch` lifts the cap;
CI workflow picks it up via libkrunfw's `patches/0*.patch` glob
(the `0999-overrides-` prefix sorts strictly after libkrunfw's own
numbered patches).
CI workflow hardening that landed alongside:
- cache key now keyed per-arch via `*_${ARCH}.patch` glob (an
aarch64 patch edit no longer invalidates the x86_64 cache);
- `config-libkrunfw*` skip pattern uses a bare suffix so future
`config-libkrunfw-tdx_${ARCH}.patch` / `-sev_` variants are also
excluded from the kernel source-patch pipeline.
User-facing knobs (`--mount` doc in run.rs, README troubleshooting
guide, ARCHITECTURE/PLAN narrative) updated to reflect the new
practical ceiling.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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