Re: [PATCH/RFC 2.6.21 2/5] ehca: ehca_uverbs.c: "proper" use of mmap

Christoph Raisch
2007-01-12T12:25:44Z

Roland Dreier wrote on 11.01.2007 20:54:58:

> > > int ehca_mmap(struct ib_ucontext *context, struct vm_area_struct
*vma)
> > > {
> >
> > Can you split this monster routine into individual functions for
> > each type of mmap please? With two helpers to get and verify the
cq/qp
> > shared by the individual sub-variants, that would also help to get rid
> > of all those magic offsets.
> >
> > Actually, this routine directly comes from ib_device.mmap - Roland,
> > can you shed some light on what's going on here?
>
> Each userspace-accessible IB device gets a single device node like
> /dev/infiniband/uverbsX. Opening that gives userspace a "context".
> One of the things userspace can do with that fd is mmap() on it --
> that was originally envisioned as a way to map a page of hardware
> registers directly in to the userspace process.
>
> It seems ehca needs to allocate lots of different things in the kernel
> via mmap(). What you're saying I guess is that ideally each of these
> would be mmap() on a different fd rather than using different
> offsets. It's a little awkward to open multiple device nodes to get
> multiple fds, since there's not a good way to attach them all to the
> same context. I guess we could create some hack to return more file
> handles, but I think that cure is worse than the disease of using
> magic offsets...
>
> Maybe longer term we need to look at a scheme like cell's spufs but
> I'm still not confident we have the RDMA interface quite ready to
> freeze at the system call level.
>
> - R.

...as Roland mentions, we're not completely free to change the filehandle
usage,
it's shared by ~5 drivers now.

I'd say lets investigate the direction of an own filesystem unless
there's no other clean solution.
We can polish the current version a bit, but that won't change the "magic
offsets".

Roland, could you take this patchset into your tree?
We hope it adresses the major security concern and vm_insert_page.

We're preparing the next patch for the yield deadlock topic with this
patchset as prereq.

Gruss / Regards . . . Christoph Raisch