Re: [Xen-devel] Debug-Registers in HVM domain destroyed

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.02.14 at 08:44, Juergen Gross <juergen.gross@xxxxxxxxxxxxxx> wrote:
> On 18.02.2014 13:56, Jan Beulich wrote:
>>>>> On 18.02.14 at 13:48, Juergen Gross <juergen.gross@xxxxxxxxxxxxxx> wrote:
>>> On 14.02.2014 14:02, Jan Beulich wrote:
>>>>>>> On 14.02.14 at 13:18, Juergen Gross <juergen.gross@xxxxxxxxxxxxxx> 
>>>>>>> wrote:
>>>>> Is this the case when the guest itself uses single stepping? Initially the
>>>>> debug trap shouldn't cause a VMEXIT, I think.
>>>>
>>>> That looks like a bug, indeed - it's missing from the initially set
>>>> exception_bitmap. Could you check whether adding this in
>>>> construct_vmcs() addresses that part of the issue? (A proper fix
>>>> would likely include further adjustments to the setting of this flag,
>>>> e.g. clearing it alongside clearing the DR intercept.) But then
>>>> again all of this already depends on cpu_has_monitor_trap_flag -
>>>> if that's set on your system, maybe you could try suppressing its
>>>> detection (by removing CPU_BASED_MONITOR_TRAP_FLAG from
>>>> the optional feature set in vmx_init_vmcs_config())?
>>>
>>> I've currently a test running with the attached patch (the bug was hit about
>>> once every 3 hours, test is running now for about 4 hours without problem).
>>> Test machine is running with Xen 4.2.3 hypervisor from SLES11 SP3.
>>
>> Which, if it continues running fine, would confirm the theory.
>> I'd like to defer to the VMX folks though for putting together a
>> proper fix then - I'd likely overlook some corner case.
> 
> Okay, theory confirmed.
> 
> Unless you want to do it, I'll start another thread with the info found so 
> far and include Jun Nakajima and Eddie Dong.

Please do. And perhaps also include Yang Z Zhang.

Jan


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