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Myasnikov Daniil
a92d7f17a0
Adds one step to the temporary topology job, ahead of the existing ones, and
changes nothing else on this branch.
Why. Across 32 archived nightly runs plus recent PR runs, every green run
carries "kvm_amd: Virtual GIF supported" in the runner's dmesg and no red run
does: 62 kubernetes suite instances without the line, zero passes, against 11
of 12 passing with it. vGIF lets a guest execute CLGI/STGI without trapping to
the hypervisor, and a guest only executes those when it is itself running a
hypervisor. In this stack that is exactly the sandbox Talos nodes hosting the
KubeVirt tenant VMs and nothing else, which is why the sandbox nodes boot
normally every single time while the tenant workers crawl. Without vGIF every
tenant-VM world switch costs the sandbox node two extra full VM exits, which
burns CPU without advancing the guest -- invisible to every resource counter,
and consistent with a runner that measures 54-73% idle with ~0.01% steal while
its nested guests freeze for tens of seconds.
The line is missing for one of two reasons with completely different owners,
and this step separates them:
parameters/vgif = Y with no dmesg line -> the CPUID bit was never exposed to
this VM by the host hypervisor, so only the cloud provider can change it
parameters/vgif = N -> the runner image turned it off, which is a one-line fix
CPUID 0x8000000A is read directly rather than inferred from whether the kernel
chose to print a line, and the neighbouring V_VMSAVE_VMLOAD and VNMI bits come
with it since they are the same class of "let the guest do it in hardware"
feature. The mitigation strings are captured for the same reason: they change
the cost of a VM exit without moving any resource counter.
Every group ends in one greppable VERDICT line so re-running this job samples
the runner pool without parsing the output. Re-runs are the point: vGIF
exposure varies between hosts of the same shape and CPU model, so the
distribution is what matters, not a single reading.
This also closes an instrumentation gap that cost the investigation a month.
runner-identity.txt, the SOFT-RED node-join marker and the KVM exit counters
were all added around 19-21 August, after every green run had already
happened, so none of them can be compared across the green/red boundary. The
only reason vGIF was visible at all is that the kvm_amd lines happen to fall
inside the 200-line dmesg tail the report keeps.
Assisted-By: Claude <noreply@anthropic.com>
Signed-off-by: Myasnikov Daniil <myasnikovdaniil2001@gmail.com>