[dpdk-dev] [EXT] Re: [PATCH] bus/pci: fix IOVA as VA mode selection

[Burakov, Anatoly]

On 09-Jul-19 4:12 PM, Thomas Monjalon wrote:
> 09/07/2019 17:02, Burakov, Anatoly:
>> When IOMMU is fully enabled (iommu=on at boot time), igb_uio will simply
>> not work. VFIO will work, whichever address mode you use.
>>
>> When IOMMU is in pass-through mode (iommu=pt at boot time), both igb_uio
>> and VFIO will work, although igb_uio will only support IOVA as PA mode.
>> Both modes will enable IOMMU, and both can run in IOVA as PA mode
>> without losing that protection.
>>
>> It's only when IOMMU is off, igb_uio will not engage IOMMU, and VFIO
>> will only work in no-IOMMU mode (thus not engaging IOMMU either), and
>> only then you lack the IOMMU protection.
> 
> Could we try to make IOMMU status clear in DPDK logs?
> Then we could check the kernel drivers loaded and give
> a compatibility status for each of them as debug logs.
> 

I don't think there is a way to know IOMMU status from DPDK. It's a 
property of the system. We can kinda-sorta check IOMMU status if we have 
VFIO driver (there's a API to check for vfio_noiommu i think), and we do 
log it into debug output, but there is no such facility for igb_uio - we 
cannot know if it does or does not engage the IOMMU. (not unless we grep 
dmesg or something)

-- 
Thanks,
Anatoly