Re: [RFC PATCH v2 15/19] mm/gup: Introduce vaddr_pin_pages()

Ira Weiny
2019-08-13T17:46:41Z

On Tue, Aug 13, 2019 at 08:47:06AM -0300, Jason Gunthorpe wrote:
> On Mon, Aug 12, 2019 at 02:48:55PM -0700, Ira Weiny wrote:
> > On Mon, Aug 12, 2019 at 09:28:14AM -0300, Jason Gunthorpe wrote:
> > > On Fri, Aug 09, 2019 at 03:58:29PM -0700, ira.weiny@intel.com wrote:
> > > > From: Ira Weiny <ira.weiny@intel.com>
> > > >
> > > > The addition of FOLL_LONGTERM has taken on additional meaning for CMA
> > > > pages.
> > > >
> > > > In addition subsystems such as RDMA require new information to be passed
> > > > to the GUP interface to track file owning information. As such a simple
> > > > FOLL_LONGTERM flag is no longer sufficient for these users to pin pages.
> > > >
> > > > Introduce a new GUP like call which takes the newly introduced vaddr_pin
> > > > information. Failure to pass the vaddr_pin object back to a vaddr_put*
> > > > call will result in a failure if pins were created on files during the
> > > > pin operation.
> > >
> > > Is this a 'vaddr' in the traditional sense, ie does it work with
> > > something returned by valloc?
> >
> > ...or malloc in user space, yes. I think the idea is that it is a user virtual
> > address.
>
> valloc is a kernel call

Oh... I thought you meant this: https://linux.die.net/man/3/valloc

>
> > So I'm open to suggestions. Jan gave me this one, so I figured it was safer to
> > suggest it...
>
> Should have the word user in it, imho

Fair enough...

user_addr_pin_pages(void __user * addr, ...) ?

uaddr_pin_pages(void __user * addr, ...) ?

I think I like uaddr...

>
> > > I also wish GUP like functions took in a 'void __user *' instead of
> > > the unsigned long to make this clear :\
> >
> > Not a bad idea. But I only see a couple of call sites who actually use a 'void
> > __user *' to pass into GUP... :-/
> >
> > For RDMA the address is _never_ a 'void __user *' AFAICS.
>
> That is actually a bug, converting from u64 to a 'user VA' needs to go
> through u64_to_user_ptr().

Fair enough.

But there are a lot of call sites throughout the kernel who have the same
bug... I'm ok with forcing u64_to_user_ptr() to use this new call if others
are.

Ira