Re: [PATCH v6 00/18] IOMMUFD Dirty Tracking

[Joao Martins <joao.m.martins@oracle.com>]

On 30/10/2024 15:57, Shameerali Kolothum Thodi wrote:
>> On 30/10/2024 15:36, Jason Gunthorpe wrote:
>>> On Wed, Oct 30, 2024 at 11:15:02PM +0800, Zhangfei Gao wrote:
>>>> hw/vfio/migration.c
>>>>     if (vfio_viommu_preset(vbasedev)) {
>>>>         error_setg(&err, "%s: Migration is currently not supported "
>>>>                    "with vIOMMU enabled", vbasedev->name);
>>>>         goto add_blocker;
>>>>     }
>>>
>>> The viommu driver itself does not support live migration, it would
>>> need to preserve all the guest configuration and bring it all back. It
>>> doesn't know how to do that yet.
>>
>> It's more of vfio code, not quite related to actually hw vIOMMU.
>>
>> There's some vfio migration + vIOMMU support patches I have to follow up
>> (v5)
> 
> Are you referring this series here?
> https://lore.kernel.org/qemu-devel/d5d30f58-31f0-1103-6956-377de34a790c@redhat.com/T/
> 
> Is that enabling migration only if Guest doesn’t do any DMA translations? 
> 
No, it does it when guest is using the sw vIOMMU too. to be clear: this has
nothing to do with nested IOMMU or if the guest is doing (emulated) dirty tracking.

When the guest doesn't do DMA translation is this patch:

https://lore.kernel.org/qemu-devel/20230908120521.50903-1-joao.m.martins@oracle.com/

>> but unexpected set backs unrelated to work delay some of my plans for
>> qemu 9.2.
>> I expect to resume in few weeks. I can point you to a branch while I don't
>> submit (provided soft-freeze is coming)
> 
> Also, I think we need a mechanism for page fault handling in case Guest handles 
> the stage 1 plus dirty tracking for stage 1 as well.
> 

I have emulation for x86 iommus to dirty tracking, but that is unrelated to L0
live migration -- It's more for testing in the lack of recent hardware. Even
emulated page fault handling doesn't affect this unless you have to re-map/map
new IOVA, which would also be covered in this series I think.

Unless you are talking about physical IOPF that qemu may terminate, though we
don't have such support in Qemu atm.