linux-kernel - Re: PFs on pages pinned with get_user

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: <1233240757.4495.94.camel@laptop>
Date:	Thu, 29 Jan 2009 15:52:37 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frank Mehnert <Frank.Mehnert@....COM>
Cc:	linux-kernel@...r.kernel.org, Avi Kivity <avi@...hat.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: PFs on pages pinned with get_user_pages()

On Thu, 2009-01-29 at 15:41 +0100, Frank Mehnert wrote:
> On Thursday 29 January 2009, Peter Zijlstra wrote:
> > On Thu, 2009-01-29 at 15:02 +0100, Frank Mehnert wrote:
> > > I'm one of the VirtualBox developers. We are trying to fix the annoying
> > > kerneloops warning 'BUG: sleeping function called from invalid context'
> > > reported by the Fedora folks. This warning occurs when do_swap_page()
> > > calls lock_page() and in_atomic() returns true.
> > >
> > > This warning appears when we touch into memory which is pinned with
> > > get_user_pages(). In VT-x/AMD-V mode we are executing some code in the
> > > context of the Linux kernel. To prevent scheduling of the current CPU
> > > core we disable the interripts. preempt_disable() would be probably the
> > > better choice but this would oops as well if CONFIG_PREEMPT is enabled.
> >
> > but to get there, you'd have to have called handle_mm_fault() which
> > requires the mmap_sem, which should also give that might_sleep()
> > warning.
> 
> The stacktrace is
> 
>   __might_sleep()
>   lock_page()
>   handle_mm_fault()
>   do_page_fault()
>   error_code
> 
> So yes, handle_mm_fault() is called. But I assume that down_read_trylock()
> succeeded before we were forced to call down_read().
> 
> > That aside, is there any reason you have to avoid scheduling? Otherwise
> > I would just allow so and be done with it.
> 
> The reason is that our code expects that to ensure syncing of the CPU
> state with the saved state. I fear it is quite difficult to change that...

Ah, is that what KVM uses the preempt notifiers for? Could you too?

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/