linux-kernel - Re: [PATCH 3/5] v2 seccomp_filters: Enable ftrace-based system call filtering

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: <4DDE99F6.4030804@redhat.com>
Date:	Thu, 26 May 2011 21:20:38 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	James Morris <jmorris@...ei.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kees Cook <kees.cook@...onical.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Will Drewry <wad@...omium.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org, gnatapov@...hat.com,
	Chris Wright <chrisw@...s-sol.org>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH 3/5] v2 seccomp_filters: Enable ftrace-based system call
 filtering

On 05/26/2011 09:15 PM, Ingo Molnar wrote:
> * Avi Kivity<avi@...hat.com>  wrote:
>
> >  On 05/26/2011 02:38 PM, Ingo Molnar wrote:
> >  >* Avi Kivity<avi@...hat.com>   wrote:
> >  >
> >  >>   >   The biggest amount of RAM is the guest RAM image - but if that is
> >  >>   >   mmap(SHARED) and mapped using hugepages then the pte overhead
> >  >>   >   from a process model is largely mitigated.
> >  >>
> >  >>   That doesn't work with memory hotplug.
> >  >
> >  >  Why not, if we do the sensible thing and restrict the size
> >  >  granularity and alignment of plugged/unplugged memory regions to
> >  >  2MB?
> >
> >  Once forked, you cannot have new shared anonymous memory, can you?
>
> We can have named shared memory.

But then the benefit of transparent huge pages goes away.

Of course, if some is working on extending transparent hugepages, the 
problem is solved.  I know there is interest in this.

> Incidentally i suggested this to Pekka just yesterday: i think we
> should consider guest RAM images to be named files on the local
> filesystem (prefixed with the disk image's name or so, for easy
> identification), this will help with debugging and with swapping as
> well. (This way guest RAM wont eat up regular anonymous swap space -
> it will be swapped to the filesystem.)

Qemu supports this via -mem-path.  The motivation was supporting 
hugetlbfs, before THP.  I can't say it was useful for debugging (but 
then qemu has a built in memory inspector and debugger, and supports 
attaching gdb to the guest).

> As a sidenote, live migration might also become possible this way: in
> theory we could freeze a guest to its RAM image - which can then be
> copied (together with the disk image) to another box as files and
> restarted there, with some some hw configuration state dumped to a
> header portion of that RAM image as well. (outside of the RAM area)

Live migration involves the guest running in parallel with its memory 
being copied over.  Even a 1GB guest will take 10s over 1GbE; any 
reasonably sized guest will take forever.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

--
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/