Re: virtio,iommu_platform=on

[Alexey Kardashevskiy]

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, 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