Amit Machhiwal <[email protected]> writes:
> On IBM POWER systems, newer processor generations can operate in > compatibility modes corresponding to earlier generations. This becomes > relevant for nested virtualization, where nested KVM guests may need to > run with a specific processor compatibility level. > > Currently, when running a nested KVM guest (L2) inside a Power11 pSeries > logical partition (L1) booted in Power10 compatibility mode, the guest > fails to boot while setting 'arch_compat'. This happens because the CPU > class is derived from the hardware PVR (via mfspr()), which reflects the > physical processor generation (Power11), rather than the effective > compatibility mode (Power10). > > As a result, userspace may request a Power11 arch_compat for the L2 > guest. However, the L1 partition, running in Power10 compatibility, has > only negotiated support up to Power10 with the Power Hypervisor (L0). > When H_GUEST_SET_STATE is invoked with a Power11 Logical PVR, the > hypervisor rejects the request, leading to a late guest boot failure: > > KVM-NESTEDv2: couldn't set guest wide elements > [..KVM reg dump..] > > This situation should be detected earlier. Rejecting unsupported > 'arch_compat' values in 'kvmppc_set_arch_compat()' avoids issuing an > invalid H_GUEST_SET_STATE hcall and provides a clearer failure mode. > > Add a check to reject Power11 'arch_compat' requests when the host is > running in Power10 compatibility mode, returning -EINVAL early instead > of deferring the failure to the hypervisor. > > Suggested-by: Vaibhav Jain <[email protected]> > Tested-by: Anushree Mathur <[email protected]> > Cc: <[email protected]> # v6.13+ > Signed-off-by: Amit Machhiwal <[email protected]> Thanks, this LGTM Reviewed-by: Vaibhav Jain <[email protected]> -- Cheers ~ Vaibhav
