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

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Message-Id: <c5e7e9c6-15ed-99fb-3cd6-81ec8f2d3dff@linux.ibm.com>
Date:   Thu, 17 Jan 2019 14:02:12 +0100
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>,
        "gerald.schaefer@...ibm.com" <gerald.schaefer@...ibm.com>
Cc:     "joro@...tes.org" <joro@...tes.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "walling@...ux.ibm.com" <walling@...ux.ibm.com>
Subject: Re: [PATCH v1] iommu/s390: Declare s390 iommu reserved regions

On 17/01/2019 10:23, Shameerali Kolothum Thodi wrote:
> Hi Pierre,
> 
>> -----Original Message-----
>> From: Pierre Morel [mailto:pmorel@...ux.ibm.com]
>> Sent: 15 January 2019 17:37
>> To: gerald.schaefer@...ibm.com
>> Cc: joro@...tes.org; linux-s390@...r.kernel.org;
>> iommu@...ts.linux-foundation.org; linux-kernel@...r.kernel.org;
>> alex.williamson@...hat.com; Shameerali Kolothum Thodi
>> <shameerali.kolothum.thodi@...wei.com>; walling@...ux.ibm.com
>> Subject: [PATCH v1] iommu/s390: Declare s390 iommu reserved regions
>>
>> 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.
> 
> Just in case you are planning to use the sysfs interface to retrieve the valid
> regions, and intend to use that in Qemu vfio path, please see the discussion
> here [1] (If you haven't seen this already)
> 
> Thanks,
> Shameer
> 
> [1] https://lists.gnu.org/archive/html/qemu-devel/2017-11/msg03651.html
>   
>> 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(+)
>>
>> --
>> 2.7.4
> 

Thanks Shameer,

Interesting discussion indeed.

AFAIK the patch series you are working on will provide a way to retrieve 
the reserved region through the VFIO IOMMU interface, using capabilities 
in the VFIO_IOMMU_GET_INFO.
Before this patch, the iommu_type1 was not able to retrieve the 
forbidden region from the s390_iommu.

See this patch is a contribution, so that these regions will appear in 
the reserved list when the VFIO_IOMM_GET_INFO will be able to report the 
information.

I am expecting to be able to to retrieve this information from the 
VFIO_IOMMU_GET_INFO syscall as soon as it is available.

Regards,
Pierre


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