Re: [PATCH v7 7/7] hw/arm/virt: Add properties to disable high memory regions

[Eric Auger <eric.auger@redhat.com>]

Hi Gavin,
On 10/30/22 00:43, Gavin Shan wrote:
> The 3 high memory regions are usually enabled by default, but they may
> be not used. For example, VIRT_HIGH_GIC_REDIST2 isn't needed by GICv2.
> This leads to waste in the PA space.
>
> Add properties ("highmem-redists", "highmem-ecam", "highmem-mmio") to
> allow users selectively disable them if needed. After that, the high
> memory region for GICv3 or GICv4 redistributor can be disabled by user,
> the number of maximal supported CPUs needs to be calculated based on
> 'vms->highmem_redists'. The follow-up error message is also improved
> to indicate if the high memory region for GICv3 and GICv4 has been
> enabled or not.
>
> Suggested-by: Marc Zyngier <maz@kernel.org>
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> Reviewed-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Eric Auger <eric.auger@redhat.com>

Thanks

Eric
> ---
>  docs/system/arm/virt.rst | 13 +++++++
>  hw/arm/virt.c            | 75 ++++++++++++++++++++++++++++++++++++++--
>  2 files changed, 86 insertions(+), 2 deletions(-)
>
> diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst
> index 4454706392..188a4f211f 100644
> --- a/docs/system/arm/virt.rst
> +++ b/docs/system/arm/virt.rst
> @@ -98,6 +98,19 @@ compact-highmem
>    Set ``on``/``off`` to enable/disable the compact layout for high memory regions.
>    The default is ``on`` for machine types later than ``virt-7.2``.
>  
> +highmem-redists
> +  Set ``on``/``off`` to enable/disable the high memory region for GICv3 or
> +  GICv4 redistributor. The default is ``on``. Setting this to ``off`` will
> +  limit the maximum number of CPUs when GICv3 or GICv4 is used.
> +
> +highmem-ecam
> +  Set ``on``/``off`` to enable/disable the high memory region for PCI ECAM.
> +  The default is ``on`` for machine types later than ``virt-3.0``.
> +
> +highmem-mmio
> +  Set ``on``/``off`` to enable/disable the high memory region for PCI MMIO.
> +  The default is ``on``.
> +
>  gic-version
>    Specify the version of the Generic Interrupt Controller (GIC) to provide.
>    Valid values are:
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index 020a95cfa2..65cff7add1 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -2095,14 +2095,20 @@ static void machvirt_init(MachineState *machine)
>      if (vms->gic_version == VIRT_GIC_VERSION_2) {
>          virt_max_cpus = GIC_NCPU;
>      } else {
> -        virt_max_cpus = virt_redist_capacity(vms, VIRT_GIC_REDIST) +
> -            virt_redist_capacity(vms, VIRT_HIGH_GIC_REDIST2);
> +        virt_max_cpus = virt_redist_capacity(vms, VIRT_GIC_REDIST);
> +        if (vms->highmem_redists) {
> +            virt_max_cpus += virt_redist_capacity(vms, VIRT_HIGH_GIC_REDIST2);
> +        }
>      }
>  
>      if (max_cpus > virt_max_cpus) {
>          error_report("Number of SMP CPUs requested (%d) exceeds max CPUs "
>                       "supported by machine 'mach-virt' (%d)",
>                       max_cpus, virt_max_cpus);
> +        if (vms->gic_version != VIRT_GIC_VERSION_2 && !vms->highmem_redists) {
> +            error_printf("Try 'highmem-redists=on' for more CPUs\n");
> +        }
> +
>          exit(1);
>      }
>  
> @@ -2371,6 +2377,49 @@ static void virt_set_compact_highmem(Object *obj, bool value, Error **errp)
>      vms->highmem_compact = value;
>  }
>  
> +static bool virt_get_highmem_redists(Object *obj, Error **errp)
> +{
> +    VirtMachineState *vms = VIRT_MACHINE(obj);
> +
> +    return vms->highmem_redists;
> +}
> +
> +static void virt_set_highmem_redists(Object *obj, bool value, Error **errp)
> +{
> +    VirtMachineState *vms = VIRT_MACHINE(obj);
> +
> +    vms->highmem_redists = value;
> +}
> +
> +static bool virt_get_highmem_ecam(Object *obj, Error **errp)
> +{
> +    VirtMachineState *vms = VIRT_MACHINE(obj);
> +
> +    return vms->highmem_ecam;
> +}
> +
> +static void virt_set_highmem_ecam(Object *obj, bool value, Error **errp)
> +{
> +    VirtMachineState *vms = VIRT_MACHINE(obj);
> +
> +    vms->highmem_ecam = value;
> +}
> +
> +static bool virt_get_highmem_mmio(Object *obj, Error **errp)
> +{
> +    VirtMachineState *vms = VIRT_MACHINE(obj);
> +
> +    return vms->highmem_mmio;
> +}
> +
> +static void virt_set_highmem_mmio(Object *obj, bool value, Error **errp)
> +{
> +    VirtMachineState *vms = VIRT_MACHINE(obj);
> +
> +    vms->highmem_mmio = value;
> +}
> +
> +
>  static bool virt_get_its(Object *obj, Error **errp)
>  {
>      VirtMachineState *vms = VIRT_MACHINE(obj);
> @@ -2996,6 +3045,28 @@ static void virt_machine_class_init(ObjectClass *oc, void *data)
>                                            "Set on/off to enable/disable compact "
>                                            "layout for high memory regions");
>  
> +    object_class_property_add_bool(oc, "highmem-redists",
> +                                   virt_get_highmem_redists,
> +                                   virt_set_highmem_redists);
> +    object_class_property_set_description(oc, "highmem-redists",
> +                                          "Set on/off to enable/disable high "
> +                                          "memory region for GICv3 or GICv4 "
> +                                          "redistributor");
> +
> +    object_class_property_add_bool(oc, "highmem-ecam",
> +                                   virt_get_highmem_ecam,
> +                                   virt_set_highmem_ecam);
> +    object_class_property_set_description(oc, "highmem-ecam",
> +                                          "Set on/off to enable/disable high "
> +                                          "memory region for PCI ECAM");
> +
> +    object_class_property_add_bool(oc, "highmem-mmio",
> +                                   virt_get_highmem_mmio,
> +                                   virt_set_highmem_mmio);
> +    object_class_property_set_description(oc, "highmem-mmio",
> +                                          "Set on/off to enable/disable high "
> +                                          "memory region for PCI MMIO");
> +
>      object_class_property_add_str(oc, "gic-version", virt_get_gic_version,
>                                    virt_set_gic_version);
>      object_class_property_set_description(oc, "gic-version",