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KarimAllah Ahmed 72a9b18629 xen: Remove event channel notification through Xen PCI platform device 
Ever since commit 254d1a3f02 ("xen/pv-on-hvm kexec: shutdown watches
from old kernel") using the INTx interrupt from Xen PCI platform
device for event channel notification would just lockup the guest
during bootup.  postcore_initcall now calls xs_reset_watches which
will eventually try to read a value from XenStore and will get stuck
on read_reply at XenBus forever since the platform driver is not
probed yet and its INTx interrupt handler is not registered yet. That
means that the guest can not be notified at this moment of any pending
event channels and none of the per-event handlers will ever be invoked
(including the XenStore one) and the reply will never be picked up by
the kernel.

The exact stack where things get stuck during xenbus_init:

-xenbus_init
 -xs_init
  -xs_reset_watches
   -xenbus_scanf
    -xenbus_read
     -xs_single
      -xs_single
       -xs_talkv

Vector callbacks have always been the favourite event notification
mechanism since their introduction in commit 38e20b07ef ("x86/xen:
event channels delivery on HVM.") and the vector callback feature has
always been advertised for quite some time by Xen that's why INTx was
broken for several years now without impacting anyone.

Luckily this also means that event channel notification through INTx
is basically dead-code which can be safely removed without impacting
anybody since it has been effectively disabled for more than 4 years
with nobody complaining about it (at least as far as I'm aware of).

This commit removes event channel notification through Xen PCI
platform device.

Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Julien Grall <julien.grall@citrix.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Ross Lagerwall <ross.lagerwall@citrix.com>
Cc: xen-devel@lists.xenproject.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-pci@vger.kernel.org
Cc: Anthony Liguori <aliguori@amazon.com>
Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
 		2016-09-30 11:44:34 +01:00
..
cpuid.h x86/xen: update cpuid.h from Xen-4.7 2016-07-25 13:30:45 +01:00
events.h xen: Remove event channel notification through Xen PCI platform device 2016-09-30 11:44:34 +01:00
hypercall.h x86/xen: Add stack frame dependency to hypercall inline asm calls 2016-02-24 08:35:41 +01:00
hypervisor.h x86/iopl/64: Properly context-switch IOPL on Xen PV 2016-03-17 09:49:26 +01:00
interface.h xen/PMU: Initialization code for Xen PMU 2015-08-20 12:25:20 +01:00
interface_32.h xen: implement XENMEM_machphys_mapping 2010-11-12 15:00:06 -08:00
interface_64.h xen: implement XENMEM_machphys_mapping 2010-11-12 15:00:06 -08:00
page-coherent.h dma-mapping: use unsigned long for dma_attrs 2016-08-04 08:50:07 -04:00
page.h xen/swiotlb: Pass addresses rather than frame numbers to xen_arch_need_swiotlb 2015-10-23 14:20:43 +01:00
pci.h xen/pcifront: Report the errors better. 2016-02-15 14:21:18 +00:00
swiotlb-xen.h xen/swiotlb: Use the swiotlb_late_init_with_tbl to init Xen-SWIOTLB late when PV PCI is used. 2012-09-17 12:58:16 -04:00
trace_types.h xen/trace: add multicall tracing 2011-07-18 15:43:26 -07:00