[Xen-devel] RE: [PATCH] [RFC] VT-d: always clean up dpci timers.

["Kay, Allen M" <allen.m.kay@xxxxxxxxx>]

Hi Tim,

Can you provide the code flow that can cause this failure?

In pci_release_devices(), pci_clean_dpci_irqs() is called before "d->need_iommu 
= 0" in deassign_device().  If this path is taken, then it should not return 
from !need_iommu(d) in pci_clean_dpci_irqs().

Allen

-----Original Message-----
From: Tim Deegan [mailto:Tim.Deegan@xxxxxxxxxx] 
Sent: Monday, July 18, 2011 9:39 AM
To: xen-devel@xxxxxxxxxxxxxxxxxxx
Cc: keir@xxxxxxx; Kay, Allen M
Subject: [PATCH] [RFC] VT-d: always clean up dpci timers.

If a VM has all its PCI devices deassigned, need_iommu(d) becomes false
but it might still have DPCI EOI timers that were init_timer()d but not
yet kill_timer()d.  That causes xen to crash later because the linked
list of inactive timers gets corrupted, e.g.:

(XEN) Xen call trace:
(XEN)    [<ffff82c480126256>] set_timer+0x1c2/0x24f
(XEN)    [<ffff82c48011fbf8>] schedule+0x129/0x5dd
(XEN)    [<ffff82c480122c1e>] __do_softirq+0x7e/0x89
(XEN)    [<ffff82c480122c9d>] do_softirq+0x26/0x28
(XEN)    [<ffff82c480153c85>] idle_loop+0x5a/0x5c
(XEN)    
(XEN) 
(XEN) ****************************************
(XEN) Panic on CPU 0:
(XEN) Assertion 'entry->next->prev == entry' failed at 
/local/scratch/tdeegan/xen-unstable.hg/xen/include:172
(XEN) ****************************************

The following patch makes sure that the domain destruction path always
clears up the DPCI state even if !needs_iommu(d). 

Although it fixes the crash for me, I'm sufficiently confused by this
code that I don't know whether it's enough.  If the dpci timer state
gets freed earlier than pci_clean_dpci_irqs() then there's still a race,
and some other function (reassign_device_ownership() ?) needs to sort
out the timers when the PCI card is deassigned.

Allen, can you comment?

Signed-off-by: Tim Deegan <Tim.Deegan@xxxxxxxxxx>

diff -r ab6551e30841 xen/drivers/passthrough/pci.c
--- a/xen/drivers/passthrough/pci.c     Mon Jul 18 10:59:44 2011 +0100
+++ b/xen/drivers/passthrough/pci.c     Mon Jul 18 17:22:48 2011 +0100
@@ -269,7 +269,7 @@ static void pci_clean_dpci_irqs(struct d
     if ( !iommu_enabled )
         return;
 
-    if ( !is_hvm_domain(d) || !need_iommu(d) )
+    if ( !is_hvm_domain(d) )
         return;
 
     spin_lock(&d->event_lock);

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