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: <20200914183436.GD30881@xz-x1>
Date:   Mon, 14 Sep 2020 14:34:36 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Jason Gunthorpe <jgg@...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 Mon, Sep 14, 2020 at 10:32:11AM -0700, Linus Torvalds wrote:
> On Mon, Sep 14, 2020 at 7:38 AM Jason Gunthorpe <jgg@...dia.com> wrote:
> >
> > I don't have a detailed explanation right now, but this patch appears
> > to be causing a regression where RDMA subsystem tests fail. Tests
> > return to normal when this patch is reverted.
> >
> > It kind of looks like the process is not seeing DMA'd data to a
> > pin_user_pages()?
> 
> I'm a nincompoop. I actually _talked_ to Hugh Dickins about this when
> he raised concerns, and I dismissed his concerns with "but PAGE_PIN is
> special".
> 
> As usual, Hugh was right. Page pinning certainly _is_ special, but
> it's not that different from the regular GUP code.
> 
> But in the meantime, I have a lovely confirmation from the kernel test
> robot, saying that commit 09854ba94c results in a
> "vm-scalability.throughput 31.4% improvement", which was what I was
> hoping for - the complexity wasn't just complexity, it was active
> badness due to the page locking horrors.
> 
> I think what we want to do is basically do the "early COW", but only
> do it for FOLL_PIN (and not turn them into writes for anything but the
> COW code). So basically redo the "enforced COW mechanism", but rather
> than do it for everything, now do it only for FOLL_PIN, and only in
> that COW path.
> 
> Peter - any chance you can look at this? I'm still looking at the page
> lock fairness performance regression, although I now think I have a
> test patch for Phoronix to test out.

Sure, I'll try to prepare something like that and share it shortly.

Thanks,

-- 
Peter Xu