linux-kernel - Re: [Xen-devel] Re: [patch 14/21] Xen-paravirt: Add XEN config options and disable unsupported config options.

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: <45D58531.4010808@vmware.com>
Date:	Fri, 16 Feb 2007 02:19:29 -0800
From:	Zachary Amsden <zach@...are.com>
To:	Keir Fraser <keir@...source.com>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	xen-devel@...ts.xensource.com, Ian Pratt <ian.pratt@...source.com>,
	Dan Hecht <dhecht@...are.com>, linux-kernel@...r.kernel.org,
	Chris Wright <chrisw@...s-sol.org>, Andi Kleen <ak@....de>,
	virtualization@...ts.osdl.org,
	Steven Hand <steven.hand@...cam.ac.uk>
Subject: Re: [Xen-devel] Re: [patch 14/21] Xen-paravirt: Add XEN config options
 and disable unsupported config options.

Keir Fraser wrote:
> On 16/2/07 07:25, "Jeremy Fitzhardinge" <jeremy@...p.org> wrote:
>
>   
>>> Oh, so that's why it doesn't break when CONFIG_PREEMPT=y.  In which case
>>> that preempt_disable() I spotted is wrong-and-unneeded.
>>>
>>> Why doesn't Xen work with preemption??
>>>       
>> I've forgotten the details.  Ian?  Keir?  Steven?  Maybe it can be done.
>>     
>
> It breaks guest save/restore for us currently because threads can be
> sleeping with machine addresses in local storage (registers, stack). There
> are a few ways to achieve an acceptable solution:
>
>  1. Put processes in the freezer when we suspend. This should avoid any
> thread being in a critical section with machine addresses in its hand. We
> haven't yet investigated the performance impact of freezing processes,
> particularly on the downtime of live relocation.
>
>  2. Allow CONFIG_PREEMPT to be compiled in, but disable it at runtime. We
> could do this by, for example, reserving a bit in preempt_count() so that
> most preemption checks do not touch any more cache lines. I guess it would
> need a bit of fixing up (e.g., so that in_atomic() would not be always
> asserted). Even better for us would be to allow switching between
> involuntary and voluntary preemption at runtime. It looks as though the hook
> points for these two techniques are not usually compiled in at the same
> time, however.
>
>   

Doesn't stop_machine_run already take care of getting you out of all 
kernel threads?  So you can only be sleeping, not preempted, in which 
case, this might not be an issue?

Zach

-
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/