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Re: [Qemu-devel] [PATCH 0/2][RFC] postcopy migration: Linux char device

From: Isaku Yamahata
Subject: Re: [Qemu-devel] [PATCH 0/2][RFC] postcopy migration: Linux char device for postcopy
Date: Fri, 30 Dec 2011 00:53:28 +0900
User-agent: Mutt/1.5.19 (2009-01-05)

On Thu, Dec 29, 2011 at 04:55:11PM +0200, Avi Kivity wrote:
> On 12/29/2011 04:49 PM, Isaku Yamahata wrote:
> > > > Great, then we agreed with list/reattach basically.
> > > > (Maybe identity scheme needs reconsideration.)
> > > 
> > > I guess we miscommunicated.  Why is reattach needed?  If you have the
> > > fd, nothing else is needed.
> >
> > What if malicious process close the fd and does page fault intentionally?
> > Unkillable process issue remains.
> > I think we are talking not only qemu case but also general case.
> It's not unkillable.  If you sleep with TASK_INTERRUPTIBLE then you can
> process signals.  This includes SIGKILL.

Hmm, you said that the fault handler doesn't resolve the page fault.

> > Don't resolve the page fault.  It's up to the user/system to make sure
> > it happens.  qemu can easily do it by watching for the daemon's death
> > and respawning it.

To kill the process, the fault handler must return resolving the fault.
It must return something. What do you expect? VM_FAULT_SIGBUS? zero page?

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