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

[Gavin Shan <gshan@redhat.com>]

Hi Connie,

On 10/19/22 10:00 PM, Cornelia Huck wrote:
> On Wed, Oct 12 2022, Gavin Shan <gshan@redhat.com> 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.
> 
> Maybe s/compact space/the compact layout/ ?
> 

Yeah, 'compact layout' is better. I will amend in next respin.

>> +  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
> 
> s/space in/layout for/ ?
> 

Agreed.

>> + * IO regions. For example, VIRT_HIGH_PCIE_MMIO can be disabled or enabled
>> + * depending on the property in the following scenario.
>> + *
>> + * 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) */
> 
> (...)
> 
>> @@ -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 */
> 
> s/space/layout/ ?
> 

Ack.

>> +    vmc->no_highmem_compact = true;
>>   }
>>   DEFINE_VIRT_MACHINE(7, 1)
>>   
> 
> Other than the wording nits, lgtm.
> 
> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
> 

Thanks,
Gavin