Re: [PATCH v5 06/32] hw/arm/smmuv3-accel: Initialize shared system address space

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

On 11/3/25 2:39 PM, Philippe Mathieu-Daudé wrote:
> Hi,
>
> On 31/10/25 11:49, Shameer Kolothum wrote:
>> To support accelerated SMMUv3 instances, introduce a shared system-wide
>> AddressSpace (shared_as_sysmem) that aliases the global system memory.
>> This shared AddressSpace will be used in a subsequent patch for all
>> vfio-pci devices behind all accelerated SMMUv3 instances within a VM.
>>
>> Signed-off-by: Shameer Kolothum <skolothumtho@nvidia.com>
>> ---
>>   hw/arm/smmuv3-accel.c | 27 +++++++++++++++++++++++++++
>>   1 file changed, 27 insertions(+)
>>
>> diff --git a/hw/arm/smmuv3-accel.c b/hw/arm/smmuv3-accel.c
>> index 99ef0db8c4..f62b6cf2c9 100644
>> --- a/hw/arm/smmuv3-accel.c
>> +++ b/hw/arm/smmuv3-accel.c
>> @@ -11,6 +11,15 @@
>>   #include "hw/arm/smmuv3.h"
>>   #include "smmuv3-accel.h"
>>   +/*
>> + * The root region aliases the global system memory, and
>> shared_as_sysmem
>> + * provides a shared Address Space referencing it. This Address
>> Space is used
>> + * by all vfio-pci devices behind all accelerated SMMUv3 instances
>> within a VM.
>> + */
>> +MemoryRegion root;
>> +MemoryRegion sysmem;
>
> Why can't we store that in SMMUv3State?
>
>> +static AddressSpace *shared_as_sysmem;

We will have several instances of SMMUv3State which all share the same
as, hence the choice of having a global.

Eric
>
> FYI we have object_resolve_type_unambiguous() to check whether an
> instance exists only once (singleton).
>
>> +
>>   static SMMUv3AccelDevice *smmuv3_accel_get_dev(SMMUState *bs,
>> SMMUPciBus *sbus,
>>                                                  PCIBus *bus, int devfn)
>>   {
>> @@ -51,9 +60,27 @@ static const PCIIOMMUOps smmuv3_accel_ops = {
>>       .get_address_space = smmuv3_accel_find_add_as,
>>   };
>>   +static void smmuv3_accel_as_init(SMMUv3State *s)
>> +{
>> +
>> +    if (shared_as_sysmem) {
>> +        return;
>> +    }
>> +
>> +    memory_region_init(&root, OBJECT(s), "root", UINT64_MAX);
>> +    memory_region_init_alias(&sysmem, OBJECT(s), "smmuv3-accel-sysmem",
>> +                             get_system_memory(), 0,
>> +                             memory_region_size(get_system_memory()));
>> +    memory_region_add_subregion(&root, 0, &sysmem);
>> +
>> +    shared_as_sysmem = g_new0(AddressSpace, 1);
>> +    address_space_init(shared_as_sysmem, &root,
>> "smmuv3-accel-as-sysmem");
>> +}
>> +
>>   void smmuv3_accel_init(SMMUv3State *s)
>>   {
>>       SMMUState *bs = ARM_SMMU(s);
>>         bs->iommu_ops = &smmuv3_accel_ops;
>> +    smmuv3_accel_as_init(s);
>>   }
>