Amit Machhiwal [off-list ref] writes:

<snip>

Introduce a validation mechanism that detects unsupported arch_compat
values early in the guest initialization path. When an unsupported
arch_compat is requested (e.g., Power11 on a Power10 compatibility mode
host), kvmppc_set_arch_compat() uses cpu_has_feature(CPU_FTR_P11_PVR) to
detect the mismatch and sets arch_compat to PVR_ARCH_INVALID. This
triggers kvmppc_sanity_check() to mark the vCPU as invalid by setting
vcpu->arch.sane to false. On the next vCPU run, kvmppc_vcpu_run_hv()
checks this flag and returns -EINVAL, preventing the guest from running
with an invalid processor compatibility configuration.

With this, when a Power11 arch_compat is requested on a Power10
compatibility mode host, the guest fails early during boot with:

  error: kvm run failed Invalid argument

<snip>

Suggested-by: Vaibhav Jain <redacted>
Cc: stable@vger.kernel.org # v6.13+
Signed-off-by: Amit Machhiwal <redacted>

Thanks Amit for addressing the issue reported on v1. The v2 patch
changes look aligned to what we discussed offline. Hence,


Reviewed-by: Vaibhav Jain <redacted>


-- 
Cheers
~ Vaibhav