linux-kernel - Re: [PATCH 1/4] mm: Trial do_wp

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200918094439.GD18920@quack2.suse.cz>
Date:   Fri, 18 Sep 2020 11:44:39 +0200
From:   Jan Kara <jack@...e.cz>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Peter Xu <peterx@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        John Hubbard <jhubbard@...dia.com>,
        Leon Romanovsky <leonro@...dia.com>,
        Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Maya B . Gokhale" <gokhale2@...l.gov>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Marty Mcfadden <mcfadden8@...l.gov>,
        Kirill Shutemov <kirill@...temov.name>,
        Oleg Nesterov <oleg@...hat.com>, Jann Horn <jannh@...gle.com>,
        Jan Kara <jack@...e.cz>, Kirill Tkhai <ktkhai@...tuozzo.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/4] mm: Trial do_wp_page() simplification

On Thu 17-09-20 19:09:00, Jason Gunthorpe wrote:
> On Thu, Sep 17, 2020 at 05:40:59PM -0400, Peter Xu wrote:
> > On Thu, Sep 17, 2020 at 01:35:56PM -0700, Linus Torvalds wrote:
> > > For that to happen, we'd need to have the vma flag so that we wouldn't
> > > have any worry about non-pinners, but as you suggested, I think even
> > > just a mm-wide counter - or flag - to deal with the fast-bup case is
> > > likely perfectly sufficient.
> > 
> > Would mm_struct.pinned_vm suffice?
> 
> I think that could be a good long term goal
> 
> IIRC last time we dug into the locked_vm vs pinned_vm mess it didn't
> get fixed. There is a mix of both kinds, as you saw, and some
> resistance I don't clearly remember to changing it.
> 
> My advice for this -rc fix is to go with a single bit in the mm_struct
> set on any call to pin_user_pages*
> 
> Then only users using pin_user_pages and forking are the only ones who
> would ever do extra COW on fork. I think that is OK for -rc, this
> workload should be rare due to the various historical issues. Anyhow,
> a slow down regression is better than a it is broken regression.

Agreed. I really like the solution of not write-protecting pinned pages on
fork(2).
 
> This can be improved into a counter later. Due to the pinned_vm
> accounting all call sites should have the mm_struct at unpin, but I
> have a feeling it will take a alot of driver patches to sort it all
> out.

I somewhat fear that some of the users of pin_user_pages() don't bother
with pinned_vm accounting exactly because they don't have mm_struct on
unpin...

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