Re: [PATCH 2/2] mm: set PG_dma_pinned on get_user_pages*()

Jan Kara
2018-06-27T17:02:54Z

On Wed 27-06-18 08:57:18, Jason Gunthorpe wrote:
> On Wed, Jun 27, 2018 at 02:42:55PM +0200, Jan Kara wrote:
> > On Wed 27-06-18 13:59:27, Michal Hocko wrote:
> > > On Wed 27-06-18 13:53:49, Jan Kara wrote:
> > > > On Wed 27-06-18 13:32:21, Michal Hocko wrote:
> > > [...]
> > > > > Appart from that, do we really care about 32b here? Big DIO, IB users
> > > > > seem to be 64b only AFAIU.
> > > >
> > > > IMO it is a bad habit to leave unpriviledged-user-triggerable oops in the
> > > > kernel even for uncommon platforms...
> > >
> > > Absolutely agreed! I didn't mean to keep the blow up for 32b. I just
> > > wanted to say that we can stay with a simple solution for 32b. I thought
> > > the g-u-p-longterm has plugged the most obvious breakage already. But
> > > maybe I just misunderstood.
> >
> > Most yes, but if you try hard enough, you can still trigger the oops e.g.
> > with appropriately set up direct IO when racing with writeback / reclaim.
>
> gup longterm is only different from normal gup if you have DAX and few
> people do, which really means it doesn't help at all.. AFAIK??

Right, what I wrote works only for DAX. For non-DAX situation g-u-p
longterm does not currently help at all. Sorry for confusion.

Honza

--
Jan Kara <jack@suse.com>
SUSE Labs, CR