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Subject: Re: [PATCH 1/4] vdpa: introduce config op to get valid iova range
To:     "Michael S. Tsirkin" <mst@redhat.com>, Eli Cohen <eli@mellanox.com>
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From:   Jason Wang <jasowang@redhat.com>
Message-ID: <20debde5-1f59-8bd4-1978-68e59abefaea@redhat.com>
Date:   Fri, 7 Aug 2020 11:23:10 +0800
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On 2020/8/6 下午8:29, Michael S. Tsirkin wrote:
> On Thu, Aug 06, 2020 at 03:03:55PM +0300, Eli Cohen wrote:
>> On Wed, Aug 05, 2020 at 08:51:56AM -0400, Michael S. Tsirkin wrote:
>>> On Wed, Jun 17, 2020 at 11:29:44AM +0800, Jason Wang wrote:
>>>> This patch introduce a config op to get valid iova range from the vDPA
>>>> device.
>>>>
>>>> Signed-off-by: Jason Wang<jasowang@redhat.com>
>>>> ---
>>>>   include/linux/vdpa.h | 14 ++++++++++++++
>>>>   1 file changed, 14 insertions(+)
>>>>
>>>> diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h
>>>> index 239db794357c..b7633ed2500c 100644
>>>> --- a/include/linux/vdpa.h
>>>> +++ b/include/linux/vdpa.h
>>>> @@ -41,6 +41,16 @@ struct vdpa_device {
>>>>   	unsigned int index;
>>>>   };
>>>>   
>>>> +/**
>>>> + * vDPA IOVA range - the IOVA range support by the device
>>>> + * @start: start of the IOVA range
>>>> + * @end: end of the IOVA range
>>>> + */
>>>> +struct vdpa_iova_range {
>>>> +	u64 start;
>>>> +	u64 end;
>>>> +};
>>>> +
>>> This is ambiguous. Is end in the range or just behind it?
>>> How about first/last?
>> It is customary in the kernel to use start-end where end corresponds to
>> the byte following the last in the range. See struct vm_area_struct
>> vm_start and vm_end fields
> Exactly my point:
>
> include/linux/mm_types.h:       unsigned long vm_end;           /* The first byte after our end address
>
> in this case Jason wants it to be the last byte, not one behind.


Ok, I somehow recall the reason :)

See:

struct iommu_domain_geometry {
     dma_addr_t aperture_start; /* First address that can be mapped    */
     dma_addr_t aperture_end;   /* Last address that can be mapped     */
     bool force_aperture;       /* DMA only allowed in mappable range? */
};


So what I proposed here is to be consistent with it.

Thanks


>
>