Re: [Qemu-devel] [Qemu-ppc] [RFC PATCH v2 4/4] spapr: Fix migration of Radix guests

[Suraj Jitindar Singh <sjitindarsingh@gmail.com>]

On Fri, 2017-05-19 at 11:10 +0530, Bharata B Rao wrote:
> Fix migration of radix guests by ensuring that we issue
> KVM_PPC_CONFIGURE_V3_MMU for radix case post migration.
> 
> Reported-by: Nageswara R Sastry <rnsastry@linux.vnet.ibm.com>
> Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> ---
>  hw/ppc/spapr.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index daf335c..8f20f14 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -1400,6 +1400,18 @@ static int spapr_post_load(void *opaque, int
> version_id)
>          err = spapr_rtc_import_offset(&spapr->rtc, spapr-
> >rtc_offset);
>      }

This will break migration for tcg radix guests.

Given that there is essentially nothing special we need to do on
incoming tcg migration, I suggest we make it:

if (spapr->patb_entry && kvm_enabled()) {
    [snip]
}

>  
> +    if (spapr->patb_entry) {
> +        PowerPCCPU *cpu = POWERPC_CPU(first_cpu);
> +        if (kvmppc_has_cap_mmu_radix() && kvm_enabled()) {

Why not make this a bit more generic? Something like:

err = kvmppc_configure_v3_mmu(cpu, !!(spapr->patb_entry & PATBE1_GR),
!!(cpu->env.spr[SPR_LPCR] & LPCR_GTSE), spapr->patb_entry);
if (err) {
    error_report("Process table config unsupported by the host");
    return -EINVAL;
}

return err;

While I don't think it's possible currently, there is nothing
inherently incorrect about having a non-zero process table entry for a
hash guest. And this saves a future update.

> +            err = kvmppc_configure_v3_mmu(cpu,
> SPAPR_PROC_TABLE_RADIX,
> +                ((cpu->env.spr[SPR_LPCR] & LPCR_GTSE) ?
> SPAPR_PROC_TABLE_GTSE :
> +                0), spapr->patb_entry);
> +        } else {
> +            error_report("Radix guest is unsupported by the host");
> +            return -EINVAL;
> +        }
> +    }
> +
>      return err;
>  }
>