Re: [Xen-devel] [PATCH V2] arm: p2m.c bug-fix: hypervisor hang on __p2m_get_mem_access

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Wed, 2016-02-03 at 13:54 +0200, Corneliu ZUZU wrote:
> On 2/3/2016 1:48 PM, Ian Campbell wrote:
> > On Wed, 2016-01-27 at 14:24 +0200, Corneliu ZUZU wrote:
> > > When __p2m_get_mem_access gets called, the p2m lock is already taken
> > > by either get_page_from_gva or p2m_get_mem_access.
> > > 
> > > Possible code paths:
> > > 1)        -> get_page_from_gva
> > >           -> p2m_mem_access_check_and_get_page
> > >                   -> __p2m_get_mem_access
> > > 2)        -> p2m_get_mem_access
> > >           -> __p2m_get_mem_access
> > > 
> > > In both cases if __p2m_get_mem_access subsequently gets to
> > > call p2m_lookup (happens if !radix_tree_lookup(...)), a hypervisor
> > > hang will occur, since p2m_lookup also spin-locks on the p2m lock.
> > > 
> > > This bug-fix simply replaces the p2m_lookup call from
> > > __p2m_get_mem_access
> > > with a call to __p2m_lookup.
> > > 
> > > Following Ian's suggestion, we also add an ASSERT to ensure that
> > > the p2m lock is taken upon __p2m_get_mem_access entry.
> > > 
> > > Signed-off-by: Corneliu ZUZU <czuzu@xxxxxxxxxxxxxxx>
> > Acked + applied, thanks.
> > 
> > 
> I thought this mail was not sent properly (didn't find it any longer on 
> the web (?)) and I resent it just earlier.
> I figured it must've been the fact that I forgot to put a "Changed since 
> v1" section & that I didn't include an
> "--in-reply-to" option. Apparently it was actually sent correctly.
> Sorry, ignore the last one (which contains a "Changed since v1" section).

OK, please check that what is currently in xen.git#staging is what you
think should be there.

Ian.


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