This might be more helpful. I ran another bisect with the following
final log:
---
git bisect start
# bad: [d6ffc6ac83b1f9f12652d89b9cb5bcbfbea7796c] x86/vector: Respect affinity mask in irq descriptor
git bisect bad d6ffc6ac83b1f9f12652d89b9cb5bcbfbea7796c
# good: [e4ae4c8ea7c65f61fde29c689d148c8c9e05305a] Merge branch 'irq/core' into x86/apic
git bisect good e4ae4c8ea7c65f61fde29c689d148c8c9e05305a
# good: [4ef76eb6de734dc03a7f3b8f80884362364e6049] x86/apic: Get rid of the legacy irq data storage
git bisect good 4ef76eb6de734dc03a7f3b8f80884362364e6049
# good: [ba801640b10d87b1c4e26cbcbe414a001255404f] x86/vector: Compile SMP only code conditionally
git bisect good ba801640b10d87b1c4e26cbcbe414a001255404f
# good: [90ad9e2d91067983f3328e21b306323877e5f48a] x86/io_apic: Reevaluate vector configuration on activate()
git bisect good 90ad9e2d91067983f3328e21b306323877e5f48a
# bad: [4900be83602b6be07366d3e69f756c1959f4169a] x86/vector/msi: Switch to global reservation mode
git bisect bad 4900be83602b6be07366d3e69f756c1959f4169a
# bad: [2db1f959d9dc16035f2eb44ed5fdb2789b754d6a] x86/vector: Handle managed interrupts proper
git bisect bad 2db1f959d9dc16035f2eb44ed5fdb2789b754d6a
# first bad commit: [2db1f959d9dc16035f2eb44ed5fdb2789b754d6a] x86/vector: Handle managed interrupts proper
---
That first bad commit 2db1f95 identified at the end is interesting:
it's the only one I've tried through all of this that actually gives
me a kernel panic when unadorned with kernel options (so unlike all of
the others it fails to even drop me at a tty login prompt).
I tried a number of things to fiddle with it: it boots fine with
either nolapic or noapic. The former results in seeing a single cpu
with lscpu, but the latter (noapic) seems to give me as much
functionality as I'd need. I'm not seeing the issue noted before,
whereby noapic for 4.15.0-rc3 was somehow disabling my ethernet card.
I hope this second bisect went down better than the last one..