LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Mike Rapoport <rppt@linux.ibm.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Borislav Petkov <bp@suse.de>
Subject: Re: [PATCH] mm/gup: continue VM_FAULT_RETRY processing event for pre-faults
Date: Wed, 22 May 2019 21:43:24 +0200	[thread overview]
Message-ID: <20190522194322.5k52docwgp5zkdcj@linutronix.de> (raw)
In-Reply-To: <20190522122113.a2edc8aba32f0fad189bae21@linux-foundation.org>

On 2019-05-22 12:21:13 [-0700], Andrew Morton wrote:
> On Tue, 14 May 2019 17:29:55 +0300 Mike Rapoport <rppt@linux.ibm.com> wrote:
> 
> > When get_user_pages*() is called with pages = NULL, the processing of
> > VM_FAULT_RETRY terminates early without actually retrying to fault-in all
> > the pages.
> > 
> > If the pages in the requested range belong to a VMA that has userfaultfd
> > registered, handle_userfault() returns VM_FAULT_RETRY *after* user space
> > has populated the page, but for the gup pre-fault case there's no actual
> > retry and the caller will get no pages although they are present.
> > 
> > This issue was uncovered when running post-copy memory restore in CRIU
> > after commit d9c9ce34ed5c ("x86/fpu: Fault-in user stack if
> > copy_fpstate_to_sigframe() fails").
> > 
> > After this change, the copying of FPU state to the sigframe switched from
> > copy_to_user() variants which caused a real page fault to get_user_pages()
> > with pages parameter set to NULL.
> 
> You're saying that argument buf_fx in copy_fpstate_to_sigframe() is NULL?

buf_fx is user stack pointer and it should not be NULL.

> If so was that expected by the (now cc'ed) developers of
> d9c9ce34ed5c8923 ("x86/fpu: Fault-in user stack if
> copy_fpstate_to_sigframe() fails")?
> 
> It seems rather odd.  copy_fpregs_to_sigframe() doesn't look like it's
> expecting a NULL argument.

exactly, this is not expected.

> Also, I wonder if copy_fpstate_to_sigframe() would be better using
> fault_in_pages_writeable() rather than get_user_pages_unlocked().  That
> seems like it operates at a more suitable level and I guess it will fix
> this issue also.

It looks, like fault_in_pages_writeable() would work. If this is the
recommendation from the MM department than I can switch to that.

> > In post-copy mode of CRIU, the destination memory is managed with
> > userfaultfd and lack of the retry for pre-fault case in get_user_pages()
> > causes a crash of the restored process.
> > 
> > Making the pre-fault behavior of get_user_pages() the same as the "normal"
> > one fixes the issue.
> 
> Should this be backported into -stable trees?

Sebastian

  reply	other threads:[~2019-05-22 19:43 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-26 17:33 [PATCH] x86/fpu: Use fault_in_pages_writeable() for pre-faulting Sebastian Andrzej Siewior
2019-05-26 17:35 ` Sebastian Andrzej Siewior
2019-05-26 19:25   ` Hugh Dickins
2019-05-28 11:54     ` My emacs problem -- was " Pavel Machek
2019-05-29  4:18 ` Andrew Morton
2019-05-29  7:25   ` [PATCH v2] " Sebastian Andrzej Siewior
2019-05-14 14:29     ` [PATCH] mm/gup: continue VM_FAULT_RETRY processing event for pre-faults Mike Rapoport
2019-05-16 16:25       ` Andrei Vagin
2019-05-21 15:53       ` Mike Rapoport
2019-05-22 19:21       ` Andrew Morton
2019-05-22 19:43         ` Sebastian Andrzej Siewior [this message]
2019-05-24 22:22           ` Hugh Dickins
2019-05-25  8:45             ` Sebastian Andrzej Siewior
2019-05-25 18:09               ` Hugh Dickins
2019-05-26 19:36                 ` Sebastian Andrzej Siewior
2019-05-26 20:17                   ` Hugh Dickins
2019-05-26 17:25             ` Pavel Machek
2019-05-22 20:38         ` Mike Rapoport
2019-05-22 21:18           ` Andrew Morton
2019-06-22 17:51             ` Andrea Arcangeli
2019-06-06 17:25       ` [tip:x86/urgent] x86/fpu: Use fault_in_pages_writeable() for pre-faulting tip-bot for Hugh Dickins
2019-05-29 21:29     ` [PATCH v2] " Chris Wilson

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20190522194322.5k52docwgp5zkdcj@linutronix.de \
    --to=bigeasy@linutronix.de \
    --cc=aarcange@redhat.com \
    --cc=akpm@linux-foundation.org \
    --cc=bp@suse.de \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=rppt@linux.ibm.com \
    --subject='Re: [PATCH] mm/gup: continue VM_FAULT_RETRY processing event for pre-faults' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).