Re: [PATCH v5 6/6] hw/arm/virt: Add 'compact-highmem' property

[Eric Auger]

Hi Gavin,

On 10/12/22 01:18, Gavin Shan wrote:
> After the improvement to high memory region address assignment is
> applied, the memory layout can be changed, introducing possible
> migration breakage. For example, VIRT_HIGH_PCIE_MMIO memory region
> is disabled or enabled when the optimization is applied or not, with
> the following configuration.
>
>   pa_bits              = 40;
>   vms->highmem_redists = false;
>   vms->highmem_ecam    = false;
>   vms->highmem_mmio    = true;
>
>   # qemu-system-aarch64 -accel kvm -cpu host    \
>     -machine virt-7.2,compact-highmem={on, off} \
>     -m 4G,maxmem=511G -monitor stdio
>
>   Region            compact-highmem=off         compact-highmem=on
>   ----------------------------------------------------------------
>   RAM               [1GB         512GB]        [1GB         512GB]
>   HIGH_GIC_REDISTS  [512GB       512GB+64MB]   [disabled]
>   HIGH_PCIE_ECAM    [512GB+256MB 512GB+512MB]  [disabled]
>   HIGH_PCIE_MMIO    [disabled]                 [512GB       1TB]
>
> In order to keep backwords compatibility, we need to disable the
> optimization on machines, which is virt-7.1 or ealier than it. It
> means the optimization is enabled by default from virt-7.2. Besides,
> 'compact-highmem' property is added so that the optimization can be
> explicitly enabled or disabled on all machine types by users.
>
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> Tested-by: Zhenyu Zhang <zhenyzha@redhat.com>
> ---
>  docs/system/arm/virt.rst |  4 ++++
>  hw/arm/virt.c            | 47 ++++++++++++++++++++++++++++++++++++++++
>  include/hw/arm/virt.h    |  1 +
>  3 files changed, 52 insertions(+)
>
> diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst
> index 20442ea2c1..75bf5a4994 100644
> --- a/docs/system/arm/virt.rst
> +++ b/docs/system/arm/virt.rst
> @@ -94,6 +94,10 @@ highmem
>    address space above 32 bits. The default is ``on`` for machine types
>    later than ``virt-2.12``.
>  
> +compact-highmem
> +  Set ``on``/``off`` to enable/disable compact space for high memory regions.
> +  The default is ``on`` for machine types later than ``virt-7.2``
> +
>  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 c05cfb5314..8f1dba0ece 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -174,6 +174,27 @@ static const MemMapEntry base_memmap[] = {
>   * Note the extended_memmap is sized so that it eventually also includes the
>   * base_memmap entries (VIRT_HIGH_GIC_REDIST2 index is greater than the last
>   * index of base_memmap).
> + *
> + * The addresses assigned to these regions are affected by 'compact-highmem'
> + * property, which is to enable or disable the compact space in the Highmem
> + * IO regions. For example, VIRT_HIGH_PCIE_MMIO can be disabled or enabled
> + * depending on the property in the following scenario.
To me you shall rather explain here what is the so-called "compact"
space vs the legacy highmem layout.

If I understand correctly the example rather legitimates the use of a
compat option showing how the layout can be affected by the option. I
would put that in the commit msg instead. Also in your example I see
VIRT_HIGH_GIC_REDISTS is disabled but the code does not disable the
region excpet if it does not fit within the PA. This does not match your
example. Also the region is named VIRT_HIGH_GIC_REDIST2.

In v4, Marc also suggested to have individual options for each highmem
region.
0f8e6a58-0dde-fb80-6966-7bb32c4df552@redhat.com/">https://lore.kernel.org/qemu-devel/0f8e6a58-0dde-fb80-6966-7bb32c4df552@redhat.com/

Have you considered that option?

Thanks

Eric
> + *
> + * pa_bits              = 40;
> + * vms->highmem_redists = false;
> + * vms->highmem_ecam    = false;
> + * vms->highmem_mmio    = true;
> + *
> + * # qemu-system-aarch64 -accel kvm -cpu host    \
> + *   -machine virt-7.2,compact-highmem={on, off} \
> + *   -m 4G,maxmem=511G -monitor stdio
> + *
> + * Region            compact-highmem=off        compact-highmem=on
> + * ----------------------------------------------------------------
> + * RAM               [1GB         512GB]        [1GB         512GB]
> + * HIGH_GIC_REDISTS  [512GB       512GB+64MB]   [disabled]
> + * HIGH_PCIE_ECAM    [512GB+256GB 512GB+512MB]  [disabled]
> + * HIGH_PCIE_MMIO    [disabled]                 [512GB       1TB]
>   */
>  static MemMapEntry extended_memmap[] = {
>      /* Additional 64 MB redist region (can contain up to 512 redistributors) 
> */
> @@ -2353,6 +2374,20 @@ static void virt_set_highmem(Object *obj, bool value, 
> Error **errp)
>      vms->highmem = value;
>  }
>  
> +static bool virt_get_compact_highmem(Object *obj, Error **errp)
> +{
> +    VirtMachineState *vms = VIRT_MACHINE(obj);
> +
> +    return vms->highmem_compact;
> +}
> +
> +static void virt_set_compact_highmem(Object *obj, bool value, Error **errp)
> +{
> +    VirtMachineState *vms = VIRT_MACHINE(obj);
> +
> +    vms->highmem_compact = value;
> +}
> +
>  static bool virt_get_its(Object *obj, Error **errp)
>  {
>      VirtMachineState *vms = VIRT_MACHINE(obj);
> @@ -2971,6 +3006,13 @@ static void virt_machine_class_init(ObjectClass *oc, 
> void *data)
>                                            "Set on/off to enable/disable 
> using "
>                                            "physical address space above 32 
> bits");
>  
> +    object_class_property_add_bool(oc, "compact-highmem",
> +                                   virt_get_compact_highmem,
> +                                   virt_set_compact_highmem);
> +    object_class_property_set_description(oc, "compact-highmem",
> +                                          "Set on/off to enable/disable 
> compact "
> +                                          "space for high memory regions");
> +
>      object_class_property_add_str(oc, "gic-version", virt_get_gic_version,
>                                    virt_set_gic_version);
>      object_class_property_set_description(oc, "gic-version",
> @@ -3055,6 +3097,7 @@ static void virt_instance_init(Object *obj)
>  
>      /* High memory is enabled by default */
>      vms->highmem = true;
> +    vms->highmem_compact = !vmc->no_highmem_compact;
>      vms->gic_version = VIRT_GIC_VERSION_NOSEL;
>  
>      vms->highmem_ecam = !vmc->no_highmem_ecam;
> @@ -3124,8 +3167,12 @@ DEFINE_VIRT_MACHINE_AS_LATEST(7, 2)
>  
>  static void virt_machine_7_1_options(MachineClass *mc)
>  {
> +    VirtMachineClass *vmc = VIRT_MACHINE_CLASS(OBJECT_CLASS(mc));
> +
>      virt_machine_7_2_options(mc);
>      compat_props_add(mc->compat_props, hw_compat_7_1, hw_compat_7_1_len);
> +    /* Compact space for high memory regions was introduced with 7.2 */
> +    vmc->no_highmem_compact = true;
>  }
>  DEFINE_VIRT_MACHINE(7, 1)
>  
> diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
> index 709f623741..c7dd59d7f1 100644
> --- a/include/hw/arm/virt.h
> +++ b/include/hw/arm/virt.h
> @@ -125,6 +125,7 @@ struct VirtMachineClass {
>      bool no_pmu;
>      bool claim_edge_triggered_timers;
>      bool smbios_old_sys_ver;
> +    bool no_highmem_compact;
>      bool no_highmem_ecam;
>      bool no_ged;   /* Machines < 4.2 have no support for ACPI GED device */
>      bool kvm_no_adjvtime;