Hi Michael,
Thanks for looking into the patch and your comments.
On 2024/02/06 09:09 PM, Michael Ellerman wrote:
> Hi Amit,
>
> One comment below ...
>
> Amit Machhiwal writes:
> > Currently, rebooting a pseries nested qemu-kvm guest (L2) results in
> > below error as L1 qemu sends PVR value 'arch_compat' == 0 via
> > ppc_set_compat ioctl. This triggers a condition failure in
> > kvmppc_set_arch_compat() resulting in an EINVAL.
> ...
> >
> > diff --git a/arch/powerpc/kvm/book3s_hv_nestedv2.c
> > b/arch/powerpc/kvm/book3s_hv_nestedv2.c
> > index 5378eb40b162..6042bdc70230 100644
> > --- a/arch/powerpc/kvm/book3s_hv_nestedv2.c
> > +++ b/arch/powerpc/kvm/book3s_hv_nestedv2.c
> > @@ -347,8 +348,26 @@ static int gs_msg_ops_vcpu_fill_info(struct
> > kvmppc_gs_buff *gsb,
> > break;
> > }
> > case KVMPPC_GSID_LOGICAL_PVR:
> > - rc = kvmppc_gse_put_u32(gsb, iden,
> > - vcpu->arch.vcore->arch_compat);
> > + /*
> > +* Though 'arch_compat == 0' would mean the default
> > +* compatibility, arch_compat, being a Guest Wide
> > +* Element, cannot be filled with a value of 0 in GSB
> > +* as this would result into a kernel trap.
> > +* Hence, when `arch_compat == 0`, arch_compat should
> > +* default to L1's PVR.
> > +*
> > +* Rework this when PowerVM supports a value of 0
> > +* for arch_compat for KVM API v2.
> > +*/
>
> Is there an actual plan that PowerVM will support this in future?
>
> If so, how will a future kernel know that it's running on a version of
> PowerVM that does support arch_compat == 0?
>
> Similarly how will we know when it's OK to drop support for this
> workaround?
I'm sending a v4 based on an off mailing list discussion.
>
> cheers
~Amit
