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

[Jason Wang]

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@xxxxxxxxxx>
> > > > ---
> > > >   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


>