Re: [Qemu-devel] [for-2.9 2/5] pseries: Stubs for HPT resizing

[David Gibson]

On Fri, Dec 09, 2016 at 11:08:02AM -0600, Michael Roth wrote:
> Quoting David Gibson (2016-12-08 20:23:11)
> > This introduces stub implementations of the H_RESIZE_HPT_PREPARE and
> > H_RESIZE_HPT_COMMIT hypercalls which we hope to add in a PAPR
> > extension to allow run time resizing of a guest's hash page table.  It
> > also adds a new machine property for controlling whether this new
> > facility is available, and logic to check that against availability
> > with KVM (only supported with KVM PR for now).
> > 
> > Finally, it adds a new string to the hypertas property in the device
> > tree, advertising to the guest the availability of the HPT resizing
> > hypercalls.  This is a tentative suggested value, and would need to be
> > standardized by PAPR before being merged.
> > 
> > Signed-off-by: David Gibson <address@hidden>
> > ---
> >  hw/ppc/spapr.c         | 66 
> > ++++++++++++++++++++++++++++++++++++++++++++++++++
> >  hw/ppc/spapr_hcall.c   | 36 +++++++++++++++++++++++++++
> >  hw/ppc/trace-events    |  2 ++
> >  include/hw/ppc/spapr.h | 11 +++++++++
> >  target-ppc/kvm.c       | 26 ++++++++++++++++++++
> >  target-ppc/kvm_ppc.h   |  5 ++++
> >  6 files changed, 146 insertions(+)
> > 
> > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > index 0f25e83..ecb0822 100644
> > --- a/hw/ppc/spapr.c
> > +++ b/hw/ppc/spapr.c
> > @@ -760,6 +760,11 @@ static void spapr_dt_rtas(sPAPRMachineState *spapr, 
> > void *fdt)
> >      if (!kvm_enabled() || kvmppc_spapr_use_multitce()) {
> >          add_str(hypertas, "hcall-multi-tce");
> >      }
> > +
> > +    if (spapr->resize_hpt != SPAPR_RESIZE_HPT_DISABLED) {
> > +        add_str(hypertas, "hcall-hpt-resize");
> > +    }
> > +
> >      _FDT(fdt_setprop(fdt, rtas, "ibm,hypertas-functions",
> >                       hypertas->str, hypertas->len));
> >      g_string_free(hypertas, TRUE);
> > @@ -1839,11 +1844,31 @@ static void ppc_spapr_init(MachineState *machine)
> >      long load_limit, fw_size;
> >      char *filename;
> >      int smt = kvmppc_smt_threads();
> > +    Error *resize_hpt_err = NULL;
> > 
> >      msi_nonbroken = true;
> > 
> >      QLIST_INIT(&spapr->phbs);
> > 
> > +    /* Check HPT resizing availability */
> > +    kvmppc_check_papr_resize_hpt(&resize_hpt_err);
> > +    if (spapr->resize_hpt == SPAPR_RESIZE_HPT_DEFAULT) {
> > +        if (resize_hpt_err) {
> > +            spapr->resize_hpt = SPAPR_RESIZE_HPT_DISABLED;
> > +            error_free(resize_hpt_err);
> > +            resize_hpt_err = NULL;
> > +        } else {
> > +            spapr->resize_hpt = smc->resize_hpt_default;
> > +        }
> > +    }
> > +
> > +    assert(spapr->resize_hpt != SPAPR_RESIZE_HPT_DEFAULT);
> > +
> > +    if ((spapr->resize_hpt != SPAPR_RESIZE_HPT_DISABLED) && 
> > resize_hpt_err) {
> > +        error_report_err(resize_hpt_err);
> > +        exit(1);
> > +    }
> 
> I'm also a bit confused by this. Aren't semantics that HPT_ENABLED will allow
> a fallback to non-resizable HPTs if the feature isn't available (whereas
> HPT_REQUIRED won't)? I don't understand how such a fallback can ever be 
> reached
> with this check in place.

We fall back if the _guest_ doesn't support HPT resizing.  This error
path is if the _host_ can't support HPT resizing.  Some extra
information about this in the reply I'll shortly send to Thomas.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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