linux-kernel - Re: [PATCH 2/2] mm: set PG_dma_pinned on get_user

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Message-ID: <20180627124255.np2a6rxy6rb6v7mm@quack2.suse.cz>
Date:   Wed, 27 Jun 2018 14:42:55 +0200
From:   Jan Kara <jack@...e.cz>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Jan Kara <jack@...e.cz>, Dan Williams <dan.j.williams@...el.com>,
        John Hubbard <jhubbard@...dia.com>,
        Christoph Hellwig <hch@....de>, Jason Gunthorpe <jgg@...pe.ca>,
        John Hubbard <john.hubbard@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        Christopher Lameter <cl@...ux.com>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-rdma <linux-rdma@...r.kernel.org>
Subject: Re: [PATCH 2/2] mm: set PG_dma_pinned on get_user_pages*()

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.

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