Re: [Qemu-devel] [PATCH 09/17] memory: iommu support

[Paolo Bonzini <pbonzini@redhat.com>]

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Il 01/05/2013 06:35, David Gibson ha scritto:
>> From: Avi Kivity <avi.kivity@gmail.com>
>> 
>> Add a new memory region type that translates addresses it is
>> given, then forwards them to a target address space.  This is
>> similar to an alias, except that the mapping is more flexible
>> than a linear translation and trucation, and also less efficient
>> since the translation happens at runtime.
>> 
>> The implementation uses an AddressSpace mapping the target region
>> to avoid hierarchical dispatch all the way to the resolved
>> region; only iommu regions are looked up dynamically.
>> 
>> Signed-off-by: Avi Kivity <avi.kivity@gmail.com> [Modified to put
>> translation in address_space_translate - Paolo] Signed-off-by:
>> Paolo Bonzini <pbonzini@redhat.com> --- exec.c                |
>> 35 +++++++++++++++++++++++++++++------ include/exec/memory.h |
>> 44 ++++++++++++++++++++++++++++++++++++++++++++ memory.c
>> |   28 ++++++++++++++++++++++++++++ 3 files changed, 101
>> insertions(+), 6 deletions(-)
> 
> [snip]
>> +void memory_region_init_iommu(MemoryRegion *mr, +
>> MemoryRegionIOMMUOps *ops, +
>> MemoryRegion *target, +                              const char
>> *name, +                              uint64_t size) +{ +
>> memory_region_init(mr, name, size); +    mr->ops = NULL; +
>> mr->iommu_ops = ops, +    mr->opaque = mr; +    mr->terminates =
>> true;  /* then re-forwards */ +    mr->destructor =
>> memory_region_destructor_iommu; +    mr->iommu_target_as =
>> g_new(AddressSpace, 1); +
>> address_space_init(mr->iommu_target_as, target);
> 
> Since IOMMUs are very likely to share a target AS (in fact, it
> will nearly always be system memory), it seems odd to me to
> construct new AddressSpace objects for each one, rather than just
> giving the AddressSpace as the parameter to
> memory_region_init_iommu.
> 

I think the problem is that we do not have reference counting, and
this makes it simpler to manage the lifetime.  It can be changed later.

Paolo
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