linux-kernel - Re: [PATCH 1/4] vdpa: introduce config op to get valid iova range

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Message-ID: <9effa14f-e305-2fa0-5aa6-83b146b969e0@redhat.com>
Date:   Wed, 12 Aug 2020 10:02:26 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Eli Cohen <eli@...lanox.com>,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, rob.miller@...adcom.com,
        lingshan.zhu@...el.com, eperezma@...hat.com, lulu@...hat.com,
        shahafs@...lanox.com, hanand@...inx.com, mhabets@...arflare.com,
        gdawar@...inx.com, saugatm@...inx.com, vmireyno@...vell.com,
        zhangweining@...jie.com.cn
Subject: Re: [PATCH 1/4] vdpa: introduce config op to get valid iova range


On 2020/8/11 下午4:29, Michael S. Tsirkin wrote:
> On Tue, Aug 11, 2020 at 10:53:09AM +0800, Jason Wang wrote:
>> On 2020/8/10 下午8:05, Michael S. Tsirkin wrote:
>>> On Thu, Aug 06, 2020 at 03:43:54PM +0300, Eli Cohen wrote:
>>>> On Thu, Aug 06, 2020 at 08:29:22AM -0400, 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@...hat.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.
>>>>>
>>>>>
>>>> Maybe start, size? Not ambiguous, and you don't need to do annoying
>>>> calculations like size = last - start + 1
>>> Size has a bunch of issues: can overlap, can not cover the entire 64 bit
>>> range. The requisite checks are arguably easier to get wrong than
>>> getting the size if you need it.
>> Yes, so do you still prefer first/last or just begin/end which is consistent
>> with iommu_domain_geometry?
>>
>> Thanks
> I prefer first/last I think, these are unambiguous.
> E.g.
>
>          dma_addr_t aperture_start; /* First address that can be mapped    */
>          dma_addr_t aperture_end;   /* Last address that can be mapped     */
>
> instead of addressing ambiguity with a comment, let's just name the field well.


Ok, will do.

Thanks



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