Re: [Xen-devel] Deadlocks by p2m_lock and event_lock

["Hao, Xudong" <xudong.hao@xxxxxxxxx>]

Hi, Tim and Andres
The patch fix part of this issue. In handle_mmio, function hvmemul_do_io() is 
called and p2m lock was held again by calling get_gfn_unshare(), still trigger 
a deadlocks.

(XEN) Xen call trace:
(XEN)    [<ffff82c4801261a3>] _spin_lock+0x1b/0xa8
(XEN)    [<ffff82c4801070d3>] notify_via_xen_event_channel+0x21/0x106
(XEN)    [<ffff82c4801b6883>] hvm_buffered_io_send+0x1f1/0x21b
(XEN)    [<ffff82c4801bbd3a>] stdvga_intercept_mmio+0x491/0x4c7
(XEN)    [<ffff82c4801b5d58>] hvm_io_intercept+0x218/0x244
(XEN)    [<ffff82c4801aa931>] hvmemul_do_io+0x55a/0x716
(XEN)    [<ffff82c4801aab1a>] hvmemul_do_mmio+0x2d/0x2f
(XEN)    [<ffff82c4801ab239>] hvmemul_write+0x181/0x1a2
(XEN)    [<ffff82c4801963f0>] x86_emulate+0xcad3/0xfbdf
(XEN)    [<ffff82c4801a9d2e>] hvm_emulate_one+0x120/0x1af
(XEN)    [<ffff82c4801b63cb>] handle_mmio+0x4e/0x1d1
(XEN)    [<ffff82c4801afd72>] hvm_hap_nested_page_fault+0x210/0x37f
(XEN)    [<ffff82c4801d2419>] vmx_vmexit_handler+0x1523/0x17d0

Thanks,
-Xudong

> -----Original Message-----
> From: Tim Deegan [mailto:tim@xxxxxxx]
> Sent: Saturday, March 10, 2012 12:56 AM
> To: Andres Lagar-Cavilla
> Cc: Hao, Xudong; Keir Fraser; xen-devel@xxxxxxxxxxxxxxxxxxx; Zhang, Xiantao;
> JBeulich@xxxxxxxx
> Subject: Re: [Xen-devel] Deadlocks by p2m_lock and event_lock
> 
> At 08:29 -0800 on 09 Mar (1331281767), Andres Lagar-Cavilla wrote:
> > >> I don't know about the event lock, but it seems unwise to call in
> > >> to handle_mmio with a gfn lock held.  How about fixing the other path?
> > >>
> > >> diff -r 04673ecb9d78 xen/arch/x86/hvm/hvm.c
> > >> --- a/xen/arch/x86/hvm/hvm.c     Thu Mar 08 16:40:05 2012 +0000
> > >> +++ b/xen/arch/x86/hvm/hvm.c     Fri Mar 09 11:15:25 2012 +0000
> > >> @@ -1324,10 +1324,11 @@ int hvm_hap_nested_page_fault(unsigned l
> > >>      if ( (p2mt == p2m_mmio_dm) ||
> > >>           (access_w && (p2mt == p2m_ram_ro)) )
> > >>      {
> > >> +        put_gfn(p2m->domain, gfn);
> > >>          if ( !handle_mmio() )
> > >>              hvm_inject_exception(TRAP_gp_fault, 0, 0);
> > >>          rc = 1;
> > >> -        goto out_put_gfn;
> > >> +        goto out;
> > >>      }
> > >>
> > >>  #ifdef __x86_64__
> > >> @@ -1379,6 +1380,7 @@ int hvm_hap_nested_page_fault(unsigned l
> > >>
> > >>  out_put_gfn:
> > >>      put_gfn(p2m->domain, gfn);
> > >> +out:
> > >>      if ( paged )
> > >>          p2m_mem_paging_populate(v->domain, gfn);
> > >>      if ( req_ptr )
> > >
> > > Yes, that's fine to release the p2m lock earlier than handle_mmio.
> >
> > Ack
> 
> OK, applied.
> 
> Tim.

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