Re: virtio,iommu_platform=on

[Alexey Kardashevskiy]

On 13/11/2019 17:23, Alexey Kardashevskiy wrote:
> 
> 
> On 13/11/2019 16:54, Michael Roth wrote:
>> Quoting Alexey Kardashevskiy (2019-11-11 21:53:49)
>>> Hi!
>>>
>>> I am enabling IOMMU for virtio in the pseries firmware (SLOF) and seeing
>>> problems, one of them is SLOF does SCSI bus scan, then it stops the
>>> virtio-scsi by clearing MMIO|IO|BUSMASTER from PCI_COMMAND (as SLOF
>>> stopped using the devices) and when this happens, I see unassigned
>>> memory access (see below) which happens because disabling busmaster
>>> disables IOMMU and QEMU cannot access the rings to do some shutdown. And
>>> when this happens, the device does not come back even if SLOF re-enables it.
>>>
>>> Hacking SLOF to not clear BUSMASTER makes virtio-scsi work but it is
>>> hardly a right fix.
>>
>> I hit the same issue enabling IOMMU for virtio-blk using this branch:
>>
>>   https://github.com/mdroth/SLOF/commits/virtio-iommu
>>
>> I just sent a tentative fix for QEMU as:
>>
>>   "virtio-pci: disable vring processing when bus-mastering is disabled"
>>
>> It's an RFC since piggy-backing off dev->broken seems a bit hacky, but
>> it seems to fix the issue at least.


btw this fixes my issue with disabling bus master as well.


>>
>> BTW, the SLOF branch above needs cleanup, but it's booting guests okay
>> and I was planning to post this week. Where are you at on yours? Maybe
>> we should sync up...
> 
> 
> Mine is here: github.com:aik/SLOF.git  virtio-iommu
> 
> Still have to debug a lot, right now virtio-net does not work :-/
> 
> Want to take over? :)
> 
> 

-- 
Alexey