[dpdk-dev] [PATCH v2] vfio: noiommu check error handling

[Maxime Coquelin]

Hi Jonas,

On 01/16/2018 05:08 PM, Jonas Pfefferle wrote:
> 
>   On Mon, 15 Jan 2018 17:11:58 +0100
>   Thomas Monjalon <thomas at monjalon.net> wrote:
>> 15/01/2018 13:22, Jonas Pfefferle:
>>>
>>>   On Sat, 13 Jan 2018 23:49:30 +0100
>>>   Thomas Monjalon <thomas at monjalon.net> wrote:
>>> > 13/01/2018 13:15, Burakov, Anatoly:
>>> >> On 11-Jan-18 11:45 PM, Thomas Monjalon wrote:
>>> >> > 07/11/2017 10:50, Jonas Pfefferle1:
>>> >> >>> Is there something urgent for 17.11?
>>> >> >>> Or can it be refined in 18.02?
>>> >> >>
>>> >> >> Nothing urgent. We can refine this for 18.02.
>>> >> >>
>>> >> >>> Anatoly, any thought?
>>> >> > >> > Anatoly, Jonas, how do you want to proceed with this patch?
>>> >> > >> >> I don't see anything to be refined here, it's a simple bug 
>>> fix - >>code >> assumes noiommu mode support is always available, 
>>> when it might not >>be >> the case on older kernels.
>>> > > As a bug fix, the title must start with "fix" and a tag "Fixes:"
>>> > must be added to help with backport.
>>> > At the same time, the explanation of the bug must be added in
>>> > the commit log please.
>>> > > Thanks
>>>
>>> It's not really a bug fix since it does not change the semantic of 
>>> the function but just adds nicer error handling.
>>> Regarding redefining the code: What I don't like is the special cases 
>>> we have to check for when using the sPAPR iommu because it does not 
>>> support VA mappings yet. I think we should decide which iova mode to 
>>> use based on the iommu types available, i.e. each iommu type should 
>>> report which iova type it supports. Thoughts?
>>
>> Have you looked at what Maxime did?
>>     https://dpdk.org/dev/patchwork/patch/33650/
>>
>> How does it affect this patch?
>>
>>
> 
> IMO it has the same problem. We shouldn't add more exception cases in 
> drivers/bus/pci/linux/pci.c but instead keep all the information about 
> what an IOMMU can do in lib/librte_eal/linuxapp/eal/eal_vfio.c

I agree adding an exception in drivers/bus/pci/linux/pci.c isn't great,
but we need first to fix a regression introduced in v17.11 LTS, and
IMHO, we cannot do a big rework as the fix is to be backported.

Once fixed, I agree we should work on a refactoring. I don't know if
eal_vfio is the right place though, as in my case for example I cannot
get the information needed through vfio ioctl().

Out of curiosity, what prevents sPAPR to use VA mode for now?

Maxime