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Re: [Qemu-devel] [PATCH V3] virtio: do not require IOMMU to be created i

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH V3] virtio: do not require IOMMU to be created in advance
Date: Thu, 9 Mar 2017 11:05:36 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0

On 09/03/2017 10:58, Jason Wang wrote:
> On 2017年03月09日 17:28, Igor Mammedov wrote:
>> On Thu, 9 Mar 2017 10:32:44 +0800
>> Jason Wang<address@hidden>  wrote:
>>> On 2017年03月09日 00:40, Igor Mammedov wrote:
>>>> On Tue, 7 Mar 2017 14:47:30 +0200
>>>> Marcel Apfelbaum<address@hidden>   wrote:
>>>>> On 03/07/2017 11:09 AM, Jason Wang wrote:
>>>>>> After commit 96a8821d2141 ("virtio: unbreak virtio-pci with IOMMU
>>>>>> after caching ring translations"), IOMMU was required to be
>>>>>> created in
>>>>>> advance. This is because we can only get the correct dma_as after pci
>>>>>> IOMMU (e.g intel_iommu) was initialized. This is suboptimal and
>>>>>> inconvenient for user. This patch releases this by:
>>>>>> - introduce a bus_master_ready method for PCIDeviceClass and trigger
>>>>>>     this during pci_init_bus_master
>>>>>> - implement virtio-pci method and 1) reset the dma_as 2) re-register
>>>>>>     the memory listener to the new dma_as
>> Instead of trying to fix up later it's possible to refuse
>> adding iommu device if other devices has been added before
>> it with -device/device_add.
>> That would match current CLI semantics where device that
>> others depend on should be listed on CLI before that others
>> are listed.
> Yes, but it works by chance in the past for the device that does not
> want bus_master_as in their realize. This change may surprise their users.

There is another posssibility.  Create the address space at init time
and add a container region instead of the bus_master_enable_region
alias.  Then at machine_done time you create the bus_master_enable_region.

This removes the need for the callbacks and makes the MemoryListener
just work.


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