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

From: Jason Wang
Subject: Re: [Qemu-devel] [PATCH V3] virtio: do not require IOMMU to be created in advance
Date: Fri, 10 Mar 2017 18:54:35 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0

On 2017年03月09日 23:32, Paolo Bonzini wrote:

On 09/03/2017 16:31, Michael S. Tsirkin wrote:
On Thu, Mar 09, 2017 at 11:05:36AM +0100, Paolo Bonzini wrote:

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.

That's definitely cleaner than a callback, though a bit tricky
so needs a good comment explaining what is going on.
And then I think we can revert
96a8821d21411f10d77ea994af369c6e5c35a2cc, right?
Yes. 96a8821d21411f10d77ea994af369c6e5c35a2cc can go then (and this is
how I expected it to work all the time---my bad).


Will prepare patches for this (probably next week).


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