linux-kernel - Re: [RFC 5/9] iov_iter: Add iov_iter_fault_in

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Message-ID: <YMVFaPZtg7ijvYe2@zeniv-ca.linux.org.uk>
Date:   Sat, 12 Jun 2021 23:38:16 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Andreas Gruenbacher <agruenba@...hat.com>,
        cluster-devel <cluster-devel@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jan Kara <jack@...e.cz>, Matthew Wilcox <willy@...radead.org>
Subject: Re: [RFC 5/9] iov_iter: Add iov_iter_fault_in_writeable()

On Sat, Jun 12, 2021 at 04:17:30PM -0700, Linus Torvalds wrote:
> On Sat, Jun 12, 2021 at 2:47 PM Al Viro <viro@...iv.linux.org.uk> wrote:
> >
> >         O_DIRECT case is a PITA - there we use GUP and there's no way
> > to tell GUP that in the current situation we do *NOT* want to hit
> > ->fault()/->page_mkwrite()/etc.  pagefault_disable() won't be even
> > noticed there...
> 
> Well, we could change that.
> 
> And we do have get_user_pages_fast_only() these days.

FWIW, I'm looking through the users of iov_iter_get_pages{,_alloc}()
right now; their semantics feels somewhat wrong.  Will follow up
when I finish looking through that pile...