kvm: Disable MSI/MSI-X in assigned device reset path

kvm: Disable MSI/MSI-X in assigned device reset path

We've hit a kernel host panic, when issuing a 'system_reset' with an
82576 nic assigned and a Windows guest. Host system is a PowerEdge R815.

[Hardware Error]: Hardware error from APEI Generic Hardware Error Source: 32993
[Hardware Error]: APEI generic hardware error status
[Hardware Error]: severity: 1, fatal
[Hardware Error]: section: 0, severity: 1, fatal
[Hardware Error]: flags: 0x01
[Hardware Error]: primary
[Hardware Error]: section_type: PCIe error
[Hardware Error]: port_type: 0, PCIe end point
[Hardware Error]: version: 1.0
[Hardware Error]: command: 0x0000, status: 0x0010
[Hardware Error]: device_id: 0000:08:00.0
[Hardware Error]: slot: 1
[Hardware Error]: secondary_bus: 0x00
[Hardware Error]: vendor_id: 0x8086, device_id: 0x10c9
[Hardware Error]: class_code: 000002
[Hardware Error]: aer_status: 0x00100000, aer_mask: 0x00018000
[Hardware Error]: Unsupported Request
[Hardware Error]: aer_layer=Transaction Layer, aer_agent=Requester ID
[Hardware Error]: aer_uncor_severity: 0x00067011
[Hardware Error]: aer_tlp_header: 40001001 0020000f edbf800c 01000000
[Hardware Error]: section: 1, severity: 1, fatal
[Hardware Error]: flags: 0x01
[Hardware Error]: primary
[Hardware Error]: section_type: PCIe error
[Hardware Error]: port_type: 0, PCIe end point
[Hardware Error]: version: 1.0
[Hardware Error]: command: 0x0000, status: 0x0010
[Hardware Error]: device_id: 0000:08:00.0
[Hardware Error]: slot: 1
[Hardware Error]: secondary_bus: 0x00
[Hardware Error]: vendor_id: 0x8086, device_id: 0x10c9
[Hardware Error]: class_code: 000002
[Hardware Error]: aer_status: 0x00100000, aer_mask: 0x00018000
[Hardware Error]: Unsupported Request
[Hardware Error]: aer_layer=Transaction Layer, aer_agent=Requester ID
[Hardware Error]: aer_uncor_severity: 0x00067011
[Hardware Error]: aer_tlp_header: 40001001 0020000f edbf800c 01000000
Kernel panic - not syncing: Fatal hardware error!
Pid: 0, comm: swapper Not tainted 2.6.32-242.el6.x86_64 #1
Call Trace:
 <NMI>  [<ffffffff814f2fe5>] ? panic+0xa0/0x168
 [<ffffffff812f919c>] ? ghes_notify_nmi+0x17c/0x180
 [<ffffffff814f91d5>] ? notifier_call_chain+0x55/0x80
 [<ffffffff814f923a>] ? atomic_notifier_call_chain+0x1a/0x20
 [<ffffffff8109667e>] ? notify_die+0x2e/0x30
 [<ffffffff814f6e81>] ? do_nmi+0x1a1/0x2b0
 [<ffffffff814f6760>] ? nmi+0x20/0x30
 [<ffffffff8103762b>] ? native_safe_halt+0xb/0x10
 <<EOE>>  [<ffffffff8101495d>] ? default_idle+0x4d/0xb0
 [<ffffffff81009e06>] ? cpu_idle+0xb6/0x110
 [<ffffffff814da63a>] ? rest_init+0x7a/0x80
 [<ffffffff81c1ff7b>] ? start_kernel+0x424/0x430
 [<ffffffff81c1f33a>] ? x86_64_start_reservations+0x125/0x129
 [<ffffffff81c1f438>] ? x86_64_start_kernel+0xfa/0x109

The root cause of the problem is that the 'reset_assigned_device()' code
first writes a 0 to the command register. Then, when qemu subsequently does
a kvm_deassign_irq() (called by assign_irq(), in the system_reset path),
the kernel ends up calling '__msix_mask_irq()', which performs a write to
the memory mapped msi vector space. Since, we've explicitly told the device
to disallow mmio access (via the 0 write to the command register), we end
up with the above 'Unsupported Request'.

The fix here is to first disable MSI-X, before doing the reset.  We also
disable MSI, leaving the device in INTx mode.  In this way, the device is
a known state after reset, and we avoid touching msi memory mapped space
on any subsequent 'kvm_deassign_irq()'.

Thanks to Michael S. Tsirkin for help in understanding what was going on
here and Jason Baron, the original debugger of this problem.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Jan Kiszka <jan.kiszka@siemens.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>