linux-kernel - Re: [PATCH v11 05/22] vfio iommu: Added pin and unpin callback functions to vfio_iommu_driver

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Date:   Wed, 9 Nov 2016 00:17:53 +0530
From:   Kirti Wankhede <kwankhede@...dia.com>
To:     Alex Williamson <alex.williamson@...hat.com>
CC:     <pbonzini@...hat.com>, <kraxel@...hat.com>, <cjia@...dia.com>,
        <qemu-devel@...gnu.org>, <kvm@...r.kernel.org>,
        <kevin.tian@...el.com>, <jike.song@...el.com>,
        <bjsdjshi@...ux.vnet.ibm.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v11 05/22] vfio iommu: Added pin and unpin callback
 functions to vfio_iommu_driver_ops



On 11/8/2016 10:09 PM, Alex Williamson wrote:
> On Tue, 8 Nov 2016 19:25:35 +0530
> Kirti Wankhede <kwankhede@...dia.com> wrote:
> 
...

>>>> -
>>>> +	int		(*pin_pages)(void *iommu_data, unsigned long *user_pfn,
>>>> +				     int npage, int prot,
>>>> +				     unsigned long *phys_pfn);
>>>> +	int		(*unpin_pages)(void *iommu_data,  
>>>
>>> Are we changing from long to int here simply because of the absurdity
>>> in passing in more than a 2^31 entry array, that would already consume
>>> more than 16GB itself?
>>>   
>>
>> These are on demand pin/unpin request, will that request go beyond 16GB
>> limit? For Nvidia vGPU solution, pin request will not go beyond this limit.
> 
> 16G is simply the size of the user_pfn or phys_pfn arrays at a maximal
> int32_t npage value, the interface actually allows mapping up to 8TB
> per call, but at that point we have 16GB of input, 16GB of output, and
> 80GB of vfio_pfns created.  So I don't really have a problem changing
> form long to int given lack of scalability in the API in general, but
> it does make me second guess the API itself.  Thanks,
> 

Changing to 'long', in future we might enhance this API without changing
it signature.

Thanks,
Kirti