Re: [Xen-devel] [xen-unstable test] 33690: regressions - FAIL

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 26/01/15 14:51, Boris Ostrovsky wrote:
> On 01/26/2015 09:49 AM, Andrew Cooper wrote:
>> On 26/01/15 11:38, Jan Beulich wrote:
>>>>>> On 26.01.15 at 12:04, <JBeulich@xxxxxxxx> wrote:
>>>>>>> On 24.01.15 at 13:54, <Ian.Jackson@xxxxxxxxxxxxx> wrote:
>>>>>   test-amd64-amd64-xl-qemut-win7-amd64  7 windows-install   fail
>>>>> REGR. vs. 33637
>>>> Jan 24 00:35:16.262627 (XEN) ----[ Xen-4.6-unstable  x86_64 
>>>> debug=y  Not tainted ]----
>>>> Jan 24 00:35:16.478599 (XEN) CPU:    1
>>>> Jan 24 00:35:16.478624 (XEN) RIP:    e008:[<0000000000000000>]
>>>> 0000000000000000
>>>> Jan 24 00:35:16.486596 (XEN) RFLAGS: 0000000000010082   CONTEXT:
>>>> hypervisor
>>>> ...
>>>> Jan 24 00:35:16.678620 (XEN) Xen call trace:
>>>> Jan 24 00:35:16.678650 (XEN)    [<ffff82d0801d36d0>]
>>>> vpmu_do_interrupt+0x2f/0x8a
>>>> Jan 24 00:35:16.686605 (XEN)    [<ffff82d08015e242>]
>>>> pmu_apic_interrupt+0x33/0x35
>>>> Jan 24 00:35:16.698582 (XEN)    [<ffff82d080171bf0>] do_IRQ+0x9c/0x624
>>>> Jan 24 00:35:16.698615 (XEN)    [<ffff82d080234062>]
>>>> common_interrupt+0x62/0x70
>>>> Jan 24 00:35:16.698653 (XEN)    [<ffff82d08012c6fe>]
>>>> _spin_unlock_irq+0x30/0x31
>>>> Jan 24 00:35:16.706604 (XEN)    [<ffff82d08012bcf1>]
>>>> __do_softirq+0x81/0x8c
>>>> Jan 24 00:35:16.706638 (XEN)    [<ffff82d08012bd49>]
>>>> do_softirq+0x13/0x15
>>>> Jan 24 00:35:16.718591 (XEN)    [<ffff82d0801ec4da>]
>>>> vmx_asm_do_vmentry+0x2a/0x50
>>> I think I see what the problem here is: Commit 8097616fbd
>>> ("x86/VPMU: handle APIC_LVTPC accesses") gives the guest
>>> control over LVTPC.mask regardless of whether the vPMU was
>>> actually initialized for it. Supposedly in the case above the
>>> guest is being run with core2_no_vpmu_ops, which in
>>> particular has .do_interrupt == NULL. It's not immediately
>>> clear whether vpmu_lvtpc_update() should do the check or its
>>> (sole) caller. In any event I'm going to revert that commit as
>>> the primary suspect for causing the regression.
>> I have just fallen over this as well.  I second a revert in the absence
>> of a clear way to fix the patch.
>
> I can't reproduce this -- neither at this patch level nor at full series.
>
> Yes, we can test for do_interrupt presence in vpmu_lvtpc_update() (or
> in vpmu_interrupt() itself) but since we cannot arm the counters
> (there is no do_wrmsr op) I am not sure I understand what can trigger
> this interrupt.
>
> -boris
>
>

As Jan explained, The patch in question allows guests (windows in both
problematic cases) to arm LVTPC, with a vpmu instance with a NULL
pointer for do_interrupt.

When a pmu apic interrupt arrives, the interrupt handler dies from a
NULL function pointer dereference.

~Andrew

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