Re: KVM Unit Test Suite Regression on AMD EPYC Turin (Zen 5)

[Sean Christopherson <seanjc@google.com>]

On Tue, Jul 08, 2025, Srikanth Aithal wrote:
> Hello all,
> KVM unit test suite for SVM is regressing on the AMD EPYC Turin platform
> (Zen 5) for a while now, even on latest linux-next[https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tag/?h=
> next-20250704]. The same seem to work fine with linux-next tag
> next-20250505.
> The TSC delay test fails intermittently (approximately once in three runs)
> with an unexpected result (expected: 50, actual: 49). This test passed
> consistently on earlier tags (e.g., next-20250505) and on non-Turin
> platforms.

Stating the obvious to some extent, I suspect it's something to do with Turin,
not a KVM issue.  This fails on our Turin hosts as far back as v6.12, i.e. long
before next-20250505 (I haven't bothered checking earlier builds), and AFAICT
the KUT test isn't doing anything to actually stress KVM itself.  I.e. I would
expect KVM bugs to manifest as blatant, 100% reproducible failures, not random
TSC slop.

  FAIL: tsc delay (expected: 50, actual: 49)
  SUMMARY: 13 tests, 1 unexpected failures
  ✘ ~/build/kut/x86 # uname -r
  6.12.0-smp--adc218676eef-tsc