[PATCH] kvm: deassign irqs in reset path

[Jason Baron <jbaron@redhat.com>]

We've hit a kernel host panic, when issuing a 'system_reset' with a 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 call kvm_deassign_irq(), before doing the reset,
and then calling assign_irq() to put the device in an INTx mode. In this
way, the device is a known state after reset (INTx mode), and we avoid touching
msi memory mapped space on any subsequent 'kvm_deassign_irq()', since we're
in INTx mode.

Thanks to Michael S. Tsirkin for help in understanding what was going on here.

Signed-off-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---
 hw/device-assignment.c |   27 +++++++++++++++++++++++++++
 1 files changed, 27 insertions(+), 0 deletions(-)

diff --git a/hw/device-assignment.c b/hw/device-assignment.c
index 89823f1..31aed17 100644
--- a/hw/device-assignment.c
+++ b/hw/device-assignment.c
@@ -1609,10 +1609,32 @@ static void reset_assigned_device(DeviceState *dev)
 {
     PCIDevice *pci_dev = DO_UPCAST(PCIDevice, qdev, dev);
     AssignedDevice *adev = DO_UPCAST(AssignedDevice, dev, pci_dev);
+    struct kvm_assigned_irq assigned_irq_data;
     char reset_file[64];
     const char reset[] = "1";
     int fd, ret;
 
+    /*
+     * Make sure the irq for the device is set to a consistent state of INTx
+     * on reset. This also ensures that a subsequent deassign_irq/assign_irq
+     * sequence (such as during 'system_reset'), does not touch memory
+     * mapped msi space, since we are about to disallow that access via a
+     * 0 write to the command register. In addition, the 'kvm_deassign_irq()'
+     * clears the msi enable bit, thus preventing any unexpected MSIs.
+     */
+    memset(&assigned_irq_data, 0, sizeof assigned_irq_data);
+    assigned_irq_data.assigned_dev_id  =
+        calc_assigned_dev_id(adev);
+    assigned_irq_data.flags = adev->irq_requested_type;
+    free_dev_irq_entries(adev);
+    ret = kvm_deassign_irq(kvm_state, &assigned_irq_data);
+    /* -ENXIO means no assigned irq */
+    if (ret && ret != -ENXIO) {
+        perror("reset_assigned_device: deassign irq");
+    }
+
+    adev->irq_requested_type = 0;
+
     snprintf(reset_file, sizeof(reset_file),
              "/sys/bus/pci/devices/%04x:%02x:%02x.%01x/reset",
              adev->host.seg, adev->host.bus, adev->host.dev, adev->host.func);
@@ -1635,6 +1657,11 @@ static void reset_assigned_device(DeviceState *dev)
      * disconnected from the PCI bus. This avoids further DMA transfers.
      */
     assigned_dev_pci_write_config(pci_dev, PCI_COMMAND, 0, 2);
+
+    ret = assign_irq(adev);
+    if (ret) {
+        perror("reset_assigned_device: assign irq");
+    }
 }
 
 static int assigned_initfn(struct PCIDevice *pci_dev)
-- 
1.7.1