Re: [Qemu-devel] [PATCH] ahci: map memory via device's address space instead of address_space_memory

[Jan Kiszka]

On 2014-07-03 12:02, Michael S. Tsirkin wrote:
> On Thu, Jul 03, 2014 at 10:43:57AM +0200, Jan Kiszka wrote:
>> On 2014-07-03 10:26, Le Tan wrote:
>>> In map_page() in hw/ide/ahci.c, replace cpu_physical_memory_map() and
>>> cpu_physical_memory_unmap() with dma_memory_map() and dma_memory_unmap(),
>>> because ahci devices should not access memory directly but via their address
>>> space. Add an AddressSpace parameter to map_page(). In order to call
>>> map_page(), we should pass the AHCIState.as as the AddressSpace argument.
>>
>> BTW, when doing "git grep cpu_physical_memory_map hw", there are some
>> more cases that should be checked (for x86). I suppose vhost is
>> incompatible with an IOMMU,
> 
> vhost can be made to work: you just need to
> update its memory tables as appropriate.
> But see below
> 
>> but plain virtio should work,
> 
> It doesn't: all guests pass in physical addresses at the moment.

You mean they do not put virtio devices into IOMMU domains, or they do
put them but ignore any translation rules that are not 1:1?

> We discussed requiring this for virtio 1.0, but in the end,
> most people thought that passing through virtio devices
> isn't worthwhile.

It should be consistent at least. If virtio is not translated, we have
to exclude such devices via ACPI tables from the scope of our IOMMUs.

> We can certainly add that as an option, with a feature bit.
> 
> If you feel otherwise, you can comment on the latest spec draft.

Does the spec at least state that "virtio devices are not subject to any
guest configured IOMMU translation"? Is is this left undefined?

Jan

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