Re: [Qemu-devel] [PATCH v3] spapr: compute default value of "hpt-max-page-size" later

[David Gibson]

On Mon, Jul 02, 2018 at 10:54:56AM +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. The
> default value must be set during machine init, because we can safely
> assume that KVM is initialized at this point.
> 
> We fix this by moving the logic to default_caps_with_cpu(). 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 to do the
> real work.
> 
> Signed-off-by: Greg Kurz <address@hidden>

Applied to ppc-for-3.0, thanks.

> ---
> v3: - moved logic to default_caps_with_cpu()
> 
> v2: - moved logic under spapr_caps_init()
> ---
>  hw/ppc/spapr.c      |   13 ++++++-------
>  hw/ppc/spapr_caps.c |   13 +++++++++++++
>  2 files changed, 19 insertions(+), 7 deletions(-)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index b2baec026ff4..062d9dc346d4 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -4095,17 +4095,16 @@ 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 machine init (see default_caps_with_cpu()).
> +     */
> +    smc->default_caps.caps[SPAPR_CAP_HPT_MAXPAGESIZE] = 0;
>  }
>  
>  DEFINE_SPAPR_MACHINE(2_12, "2.12", false);
> diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
> index 62663ebdf51a..aa605cea9108 100644
> --- a/hw/ppc/spapr_caps.c
> +++ b/hw/ppc/spapr_caps.c
> @@ -465,6 +465,19 @@ static sPAPRCapabilities 
> default_caps_with_cpu(sPAPRMachineState *spapr,
>          caps.caps[SPAPR_CAP_IBS] = SPAPR_CAP_BROKEN;
>      }
>  
> +    /* This is for pseries-2.12 and older */
> +    if (smc->default_caps.caps[SPAPR_CAP_HPT_MAXPAGESIZE] == 0) {
> +        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 */
> +        }
> +
> +        caps.caps[SPAPR_CAP_HPT_MAXPAGESIZE] = mps;
> +    }
> +
>      return caps;
>  }
>  
> 

-- 
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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