Re: [PATCH v3 1/2] s390x/pci: add support for guests that request direct mapping

[Matthew Rosato]

>>   +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
>