>> +void s390_pci_iommu_dm_enable(S390PCIIOMMU *iommu)
>> +{
>> + MachineState *ms = MACHINE(qdev_get_machine());
>> + S390CcwMachineState *s390ms = S390_CCW_MACHINE(ms);
>> +
>> + /*
>> + * For direct-mapping we must map the entire guest address space.
>> Rather
>> + * than using an iommu, create a memory region alias that maps GPA X to
>> + * iova X + SDMA. VFIO will handle pinning via its memory listener.
>> + */
>> + g_autofree char *name = g_strdup_printf("iommu-dm-s390-%04x",
>> + iommu->pbdev->uid);
>> + memory_region_init_alias(&iommu->dm_mr, OBJECT(&iommu->mr), name,
>> ms->ram,
>> + 0, s390_get_memory_limit(s390ms));
>
> Hm, the memory limit can exceed ms->ram.
>
> Would it be possible to use get_system_memory() here, such that whatever is
> mapped into physical address space (including virtio-mem devices etc) would
> simply be aliased with an offset?
>
> Or does that blow up elsewhere?
Testing with
memory_region_init_alias(&iommu->dm_mr, OBJECT(&iommu->mr), name,
get_system_memory(), 0,
s390_get_memory_limit(s390ms));
Looks good so far, will change for next version
>
> target/i386/kvm/kvm.c seems to do that:
>
> memory_region_init_alias(&smram_as_mem, OBJECT(kvm_state), "mem-smram",
> get_system_memory(), 0, ~0ull);
>
> and target/i386/tcg/system/tcg-cpu.c
>
