Re: [Qemu-devel] [PATCH] kvm: deassign irqs in reset path

[Jan Kiszka <jan.kiszka@web.de>]

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On 2012-03-30 22:13, Jason Baron wrote:
> On Fri, Mar 30, 2012 at 09:29:23PM +0200, Jan Kiszka wrote:
>> On 2012-03-30 21:18, Jason Baron wrote:
>>> 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,
>>
>> s/fix/workaround/. This is a kernel bug if userspace can crash the
>> system like this, no? Let's fix the kernel first and then look at what
>> needs to be changed here.
>>
>> Jan
>>
> 
> But don't I need special privalege to run the device assignment bits?

Yes, but even that might be moderated by a management component like
libvirt.

> For example, this crash is precipitated by a write of '0' to the pci
> device config register from userspace. Surely, not every is allowed to
> do that write. So it seems to me, that this patch is in keeping with the
> current model of how things work.

No user should needlessly be able to crash the host by issuing valid
commands in a special order.

Jan


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