RE: [RFC PATCH v2] uacce: Add uacce_ctrl misc device

[Song Bao Hua (Barry Song)]

> -----Original Message-----
> From: Jason Gunthorpe [mailto:jgg@xxxxxxxx]
> Sent: Tuesday, February 2, 2021 12:44 PM
> To: Tian, Kevin <kevin.tian@xxxxxxxxx>
> Cc: Song Bao Hua (Barry Song) <song.bao.hua@xxxxxxxxxxxxx>; chensihang (A)
> <chensihang1@xxxxxxxxxxxxx>; Arnd Bergmann <arnd@xxxxxxxx>; Greg
> Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx;
> iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx; Zhangfei Gao
> <zhangfei.gao@xxxxxxxxxx>; Liguozhu (Kenneth) <liguozhu@xxxxxxxxxxxxx>;
> linux-accelerators@xxxxxxxxxxxxxxxx
> Subject: Re: [RFC PATCH v2] uacce: Add uacce_ctrl misc device
> 
> On Fri, Jan 29, 2021 at 10:09:03AM +0000, Tian, Kevin wrote:
> > > SVA is not doom to work with IO page fault only. If we have SVA+pin,
> > > we would get both sharing address and stable I/O latency.
> >
> > Isn't it like a traditional MAP_DMA API (imply pinning) plus specifying
> > cpu_va of the memory pool as the iova?
> 
> I think their issue is the HW can't do the cpu_va trick without also
> involving the system IOMMU in a SVA mode
> 
> It really is something that belongs under some general /dev/sva as we
> talked on the vfio thread

AFAIK, there is no this /dev/sva so /dev/uacce is an uAPI
which belongs to sva.

Another option is that we add a system call like
fs/userfaultfd.c, and move the file_operations and  ioctl
to the anon inode by creating fd via anon_inode_getfd().
Then nothing will be buried by uacce.

> 
> Jason

Thanks
Barry