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

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Date:   Thu, 6 Aug 2020 08:29:22 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Eli Cohen <eli@...lanox.com>
Cc:     Jason Wang <jasowang@...hat.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 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.


> > 
> > 
> > 
> > >  /**
> > >   * vDPA_config_ops - operations for configuring a vDPA device.
> > >   * Note: vDPA device drivers are required to implement all of the
> > > @@ -134,6 +144,9 @@ struct vdpa_device {
> > >   * @get_generation:		Get device config generation (optional)
> > >   *				@vdev: vdpa device
> > >   *				Returns u32: device generation
> > > + * @get_iova_range:		Get supported iova range (on-chip IOMMU)
> > > + *				@vdev: vdpa device
> > > + *				Returns the iova range supported by the device
> > >   * @set_map:			Set device memory mapping (optional)
> > >   *				Needed for device that using device
> > >   *				specific DMA translation (on-chip IOMMU)
> > > @@ -195,6 +208,7 @@ struct vdpa_config_ops {
> > >  	void (*set_config)(struct vdpa_device *vdev, unsigned int offset,
> > >  			   const void *buf, unsigned int len);
> > >  	u32 (*get_generation)(struct vdpa_device *vdev);
> > > +	struct vdpa_iova_range (*get_iova_range)(struct vdpa_device *vdev);
> > >  
> > >  	/* DMA ops */
> > >  	int (*set_map)(struct vdpa_device *vdev, struct vhost_iotlb *iotlb);
> > > -- 
> > > 2.20.1
> >