Re: [Qemu-devel] [PATCH 2/3] spapr: compute default value of "hpt-max-page-size" later

[David Gibson]

On Thu, Jun 28, 2018 at 12:15:14PM +0200, Greg Kurz wrote:
> It is currently not possible to run a pseries-2.12 or older machine
> with HV KVM. QEMU prints the following and exits right away.
> 
> qemu-system-ppc64: KVM doesn't support for base page shift 34
> 
> The "hpt-max-page-size" capability was recently added to spapr to hide
> host configuration details from HPT mode guests. Its default value for
> newer machine types is 64k.
> 
> For backwards compatibility, pseries-2.12 and older machine types need
> a different value. This is handled as usual in a class init function.
> The default value is 16G, ie, all page sizes supported by POWER7 and
> newer CPUs, but HV KVM requires guest pages to be hpa contiguous as
> well as gpa contiguous. The default value is the page size used to
> back the guest RAM in this case.
> 
> Unfortunately kvmppc_hpt_needs_host_contiguous_pages()->kvm_enabled() is
> called way before KVM init and returns false, even if the user requested
> KVM. We thus end up selecting 16G, which isn't supported by HV KVM.
> 
> We fix this by moving the logic to spapr_machine_init() because this
> is the earliest call where we're sure kvm_enabled() can be trusted.
> Since the user cannot pass cap-hpt-max-page-size=0, we set the default
> to 0 in the pseries-2.12 class init function and use that as a flag
> in spapr_machine_init() to do the real work.
> 
> Signed-off-by: Greg Kurz <address@hidden>
> ---
>  hw/ppc/spapr.c |   25 ++++++++++++++++++-------
>  1 file changed, 18 insertions(+), 7 deletions(-)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 8cc996d0b822..1eb45cd8c424 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -2527,6 +2527,18 @@ static void spapr_machine_init(MachineState *machine)
>      QLIST_INIT(&spapr->phbs);
>      QTAILQ_INIT(&spapr->pending_dimm_unplugs);
>  
> +    /* This is for pseries-2.12 and older machine types */
> +    if (!smc->default_caps.caps[SPAPR_CAP_HPT_MAXPAGESIZE]) {
> +        uint8_t mps;
> +
> +        if (kvmppc_hpt_needs_host_contiguous_pages()) {
> +            mps = ctz64(qemu_getrampagesize());
> +        } else {
> +            mps = 34; /* allow everything up to 16GiB, i.e. everything */
> +        }
> +        smc->default_caps.caps[SPAPR_CAP_HPT_MAXPAGESIZE] = mps;
> +    }
> +

The logic above should be folded into spapr_caps_init().

>      /* Determine capabilities to run with */
>      spapr_caps_init(spapr);
>  
> @@ -4103,17 +4115,16 @@ static void 
> spapr_machine_2_12_instance_options(MachineState *machine)
>  static void spapr_machine_2_12_class_options(MachineClass *mc)
>  {
>      sPAPRMachineClass *smc = SPAPR_MACHINE_CLASS(mc);
> -    uint8_t mps;
>  
>      spapr_machine_3_0_class_options(mc);
>      SET_MACHINE_COMPAT(mc, SPAPR_COMPAT_2_12);
>  
> -    if (kvmppc_hpt_needs_host_contiguous_pages()) {
> -        mps = ctz64(qemu_getrampagesize());
> -    } else {
> -        mps = 34; /* allow everything up to 16GiB, i.e. everything */
> -    }
> -    smc->default_caps.caps[SPAPR_CAP_HPT_MAXPAGESIZE] = mps;
> +    /* We depend on kvm_enabled() to choose a default value for the
> +     * hpt-max-page-size capability. Of course we can't do it here
> +     * because this is too early and the HW accelerator isn't initialzed
> +     * yet. Postpone this to spapr_machine_init().
> +     */
> +    smc->default_caps.caps[SPAPR_CAP_HPT_MAXPAGESIZE] = 0;
>  }
>  
>  DEFINE_SPAPR_MACHINE(2_12, "2.12", false);
> 

-- 
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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