linux-kernel - Re: [PATCH v1] iommu/s390: Declare s390 iommu reserved regions

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Message-Id: <3cd790d6-aa6f-e817-27ce-56d7a9b6b6e5@linux.ibm.com>
Date:   Fri, 18 Jan 2019 14:29:20 +0100
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Robin Murphy <robin.murphy@....com>, gerald.schaefer@...ibm.com
Cc:     linux-s390@...r.kernel.org, walling@...ux.ibm.com,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        alex.williamson@...hat.com,
        Jean-Philippe Brucker <jean-philippe.brucker@....com>
Subject: Re: [PATCH v1] iommu/s390: Declare s390 iommu reserved regions

On 17/01/2019 14:02, Robin Murphy wrote:
> On 15/01/2019 17:37, Pierre Morel wrote:
>> The s390 iommu can only allow DMA transactions between the zPCI device
>> entries start_dma and end_dma.
>>
>> Let's declare the regions before start_dma and after end_dma as
>> reserved regions using the appropriate callback in iommu_ops.
>>
>> The reserved region may later be retrieved from sysfs or from
>> the vfio iommu internal interface.
> 
> For this particular case, I think the best solution is to give VFIO the 
> ability to directly interrogate the domain geometry (which s390 appears 
> to set correctly already). The idea of reserved regions was really for 
> 'unexpected' holes inside the usable address space - using them to also 
> describe places that are entirely outside that address space rather 
> confuses things IMO.
> 
> Furthermore, even if we *did* end up going down the route of actively 
> reserving addresses beyond the usable aperture, it doesn't seem sensible 
> for individual drivers to do it themselves when the core API already 
> describes the relevant information generically.
> 
> Robin.

Robin,

I already posted a patch retrieving the geometry through 
VFIO_IOMMU_GET_INFO using a specific capability for the geometry [1], 
and AFAIU, Alex did not agree with this.

What is different in what you propose?

@Alex: I was hoping that this patch goes in your direction. What do you 
think?

Thanks,
Pierre

[1]: https://lore.kernel.org/patchwork/patch/1030369/

> 
>>
>> This seems to me related with the work Shameer has started on
>> vfio_iommu_type1 so I add Alex and Shameer to the CC list.
>>
>>
>> Pierre Morel (1):
>>    iommu/s390: Declare s390 iommu reserved regions
>>
>>   drivers/iommu/s390-iommu.c | 29 +++++++++++++++++++++++++++++
>>   1 file changed, 29 insertions(+)
>>
> 


-- 
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany