Re: [PATCH 0/8] s390x/pci: Fixing s390 vfio-pci ISM support

[Cornelia Huck]

On Thu, 21 Jan 2021 15:54:22 +0100
Niklas Schnelle <schnelle@linux.ibm.com> wrote:

> On 1/21/21 3:46 PM, Pierre Morel wrote:
> > 
> > 
> > On 1/21/21 2:37 PM, Niklas Schnelle wrote:  
> >>
> >>
> >> On 1/21/21 1:30 PM, Pierre Morel wrote:  
> >   
> >>>>
> >>>> Just wanted to say that we've had a very similar discussion with
> >>>> Cornelia end of last year and came to the conclusion that explicitly
> >>>> matching the PFT is likely the safest bet:
> >>>> https://lkml.org/lkml/2020/12/22/479  
> >>>
> >>> What I see there is a discussion on the relation between relaxed access 
> >>> and MIO without explaining to Connie that we have in the kernel the 
> >>> possibility to know if a device support MIO or not independently of it 
> >>> supports the relaxed access.
> >>>
> >>> The all point here is about taking decisions for the right reasons.
> >>>
> >>> We have the possibility to take the decision based on functionalities and 
> >>> not on a specific PCI function.  
> >>
> >> Yes but that goes both ways the functionality of the region has to match
> >> that of the device and at least in it's current state the regions 
> >> functionality
> >> matches only ISM in a way that is so specific that it is very unlikely to 
> >> match anything
> >> else. For example it can't support a PCI device that requires non-MIO but
> >> also MSI-X. In its current form it doesn't even support PCI Store only PCI 
> >> Store
> >> Block, we had that in an earlier version and it's trivial but then we get 
> >> the MSI-X
> >> problem.  
> > 
> > 
> > What does that change if we take one or the other solution considering the 
> > checking of MIO/MSIX/relax versus PFT?  
> 
> 
> If it's !MIO && !MSIX && relax_align I'm fine with that check but
> then we should also add PCISTG to the region.
> 

Just to double check: that would today cover only ISM (which doesn't
use PCISTG), correct?

/me getting a bit lost in this discussion :)