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Re: [qemu-s390x] [PATCH] s390x: Fence huge pages prior to 3.1


From: David Hildenbrand
Subject: Re: [qemu-s390x] [PATCH] s390x: Fence huge pages prior to 3.1
Date: Fri, 28 Sep 2018 13:16:44 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0

On 28/09/2018 11:34, Janosch Frank wrote:
> As the kernel has no way of disallowing the start of a huge page
> backed VM, we can migrate a running huge backed VM to a host that has
> no huge page KVM support.
> 
> Let's glue huge page support support to the 3.1 machine, so we do not
> migrate to a destination host that doesn't have QEMU huge page support
> and can stop migration if KVM doesn't indicate support.
> 
> Signed-off-by: Janosch Frank <address@hidden>
> ---
>  hw/s390x/s390-virtio-ccw.c         | 10 ++++++++++
>  include/hw/s390x/s390-virtio-ccw.h |  3 +++
>  target/s390x/kvm.c                 |  6 ++++++
>  3 files changed, 19 insertions(+)
> 
> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> index f0f7fdcadd..53fd7c975f 100644
> --- a/hw/s390x/s390-virtio-ccw.c
> +++ b/hw/s390x/s390-virtio-ccw.c
> @@ -456,6 +456,7 @@ static void ccw_machine_class_init(ObjectClass *oc, void 
> *data)
>      s390mc->ri_allowed = true;
>      s390mc->cpu_model_allowed = true;
>      s390mc->css_migration_enabled = true;
> +    s390mc->hpage_1m_allowed = true;
>      mc->init = ccw_init;
>      mc->reset = s390_machine_reset;
>      mc->hot_add_cpu = s390_hot_add_cpu;
> @@ -535,6 +536,12 @@ bool cpu_model_allowed(void)
>      return get_machine_class()->cpu_model_allowed;
>  }
>  
> +bool hpage_1m_allowed(void)
> +{
> +    /* for "none" machine this results in true */
> +    return get_machine_class()->hpage_1m_allowed;
> +}
> +
>  static char *machine_get_loadparm(Object *obj, Error **errp)
>  {
>      S390CcwMachineState *ms = S390_CCW_MACHINE(obj);
> @@ -747,6 +754,9 @@ static void ccw_machine_3_0_instance_options(MachineState 
> *machine)
>  
>  static void ccw_machine_3_0_class_options(MachineClass *mc)
>  {
> +    S390CcwMachineClass *s390mc = S390_MACHINE_CLASS(mc);
> +
> +    s390mc->hpage_1m_allowed = false;
>      ccw_machine_3_1_class_options(mc);
>      SET_MACHINE_COMPAT(mc, CCW_COMPAT_3_0);
>  }
> diff --git a/include/hw/s390x/s390-virtio-ccw.h 
> b/include/hw/s390x/s390-virtio-ccw.h
> index e9c4f4182b..8aa27199c9 100644
> --- a/include/hw/s390x/s390-virtio-ccw.h
> +++ b/include/hw/s390x/s390-virtio-ccw.h
> @@ -39,12 +39,15 @@ typedef struct S390CcwMachineClass {
>      bool ri_allowed;
>      bool cpu_model_allowed;
>      bool css_migration_enabled;
> +    bool hpage_1m_allowed;
>  } S390CcwMachineClass;
>  
>  /* runtime-instrumentation allowed by the machine */
>  bool ri_allowed(void);
>  /* cpu model allowed by the machine */
>  bool cpu_model_allowed(void);
> +/* 1M huge page mappings allowed by the machine */
> +bool hpage_1m_allowed(void);
>  
>  /**
>   * Returns true if (vmstate based) migration of the channel subsystem
> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
> index 348e8cc546..323cb00e6a 100644
> --- a/target/s390x/kvm.c
> +++ b/target/s390x/kvm.c
> @@ -292,6 +292,12 @@ static int kvm_s390_configure_mempath_backing(KVMState 
> *s)
>          return 0;
>      }
>  
> +    if (!hpage_1m_allowed()) {
> +        error_report("This QEMU machine does not support huge page "
> +                     "mappings");
> +        return -EINVAL;
> +    }
> +
>      if (path_psize != 1 * MiB) {
>          error_report("Memory backing with 2G pages was specified, "
>                       "but KVM does not support this memory backing");
> 

Yes, this makes sense.

Reviewed-by: David Hildenbrand <address@hidden>

-- 

Thanks,

David / dhildenb



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