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

From: Niklas Schnelle
Subject: Re: [PATCH 0/8] s390x/pci: Fixing s390 vfio-pci ISM support
Date: Thu, 21 Jan 2021 15:54:22 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0

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.

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