Re: [kvm-unit-tests PATCH] x86/msr: Disable PMU for MSR tests

[Sean Christopherson <seanjc@google.com>]

On Thu, Sep 17, 2026, Jeremiah McReynolds wrote:
> QEMUv11 introduced a check when PMU is enabled to ensure that the
> virtualized CPU is the same as the underlying host CPU[1]. The MSR test
> always runs under GenuineIntel with the max CPU model, so PMU is
> implicitly enabled. However, when run on AMD, this new check in QEMU
> causes the test to fail with the log: "host doesn't support requested
> feature: vPMU".
> 
> Explicitly disable PMU on the MSR test to avoid this failure.
> 
> [1]: https://gitlab.com/qemu-project/qemu/-/commit/4c7f05232cd1db5db114d36be2b210d24f1b9ad3
> 
> Signed-off-by: Jeremiah McReynolds <jmcrey@google.com>
> ---
>  x86/unittests.cfg | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/x86/unittests.cfg b/x86/unittests.cfg
> index ae731a93..06fe92f9 100644
> --- a/x86/unittests.cfg
> +++ b/x86/unittests.cfg
> @@ -174,9 +174,10 @@ arch = x86_64
>  # Use GenuineIntel to ensure SYSENTER MSRs are fully preserved, and to test
>  # SVM emulation of Intel CPU behavior.  Use the max CPU model so that 64-bit
>  # support follows the host kernel.  Running a 32-bit guest on a 64-bit host
> -# will fail due to shortcomings in KVM.
> +# will fail due to shortcomings in KVM.  The max CPU model turns on PMU, but
> +# Intel PMU registers cannot be virtualized on AMD, so turn it off.
>  file = msr.flat
> -qemu_params = -cpu max,vendor=GenuineIntel
> +qemu_params = -cpu max,vendor=GenuineIntel,pmu=off

I double checked that "pmu" has existed for a while; it goes back all the way to
QEMU v1.6.0, so we should be good on that front.

>  
>  [msr64]
>  # Same as above, but with a minimal 64-bit CPU model to validate cases where an
> -- 
> 2.55.0.1082.g2b9226bbc0-goog
>