RE: [Xen-devel] mem_sharing: summarized problems when domain is dying

[MaoXiaoyun <tinnycloud@xxxxxxxxxxx>]

Hi George:
 
  Appreciate for your kindly help.
 
 I think the page type should be changed inside mem_sharing_unshare_page() in shr_lock too
,to prevent someone might unshare the page again. So your patch and mine makes the whole solution.
 
As for my patch, it seems that use put_page_and_type(page); to clean the page is enough, and 
don't need to   BUG_ON(set_shared_p2m_entry_invalid(d, gfn)==0); ( which actually calls
set_p2m_entry(d, gfn, _mfn(INVALID_MFN), 0, p2m_invalid)  ), right?
 
One another thing is rcu_lock_domain_by_id(d->domain_id);  When someone hold this lock,
d->is_dying = 0, does this mean  d->is_dying will not be changed untill it call rcu_unlock_domain?
That is to say, the lock actually protects whole d structure?

 
> Date: Fri, 21 Jan 2011 16:41:47 +0000
> Subject: Re: [Xen-devel] mem_sharing: summarized problems when domain is dying
> From: George.Dunlap@xxxxxxxxxxxxx
> To: juihaochiang@xxxxxxxxx
> CC: Tim.Deegan@xxxxxxxxxx; tinnycloud@xxxxxxxxxxx; xen-devel@xxxxxxxxxxxxxxxxxxx
>
> Tim / Xiaoyun, do you think something like this might work?
>
> -George
>
> On Fri, Jan 21, 2011 at 4:32 PM, George Dunlap <dunlapg@xxxxxxxxx> wrote:
> > [sorry, accidentally sent too early]
> >
> > On Fri, Jan 21, 2011 at 4:29 PM, George Dunlap <dunlapg@xxxxxxxxx> wrote:
> >> I'm not sure the exact rationale behind the "cannot fail" flag; but it
> >> looks like in grant_table.c, both callers of gfn_to_mfn_unshare()
> >> handle the case where the returned p2m entry is just
> >
> > ...invalid.  I wonder if "unsharing" the page, but marking the entr y
> > invalid during death would help.
> >
> > I suppose the problem there is that if you're keeping the VM around
> > but paused for analysis, you'll have holes in your address space.  But
> > just returning an invalid entry to the callers who try to unshare
> > pages might work.
> >
> >  -George
> >

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