Re: Detecting deadlocks with hypervisor..

[Anthony Liguori <aliguori@us.ibm.com>]

T S wrote:
>> Take a look at linux-2.6-sparse/drivers/core/reboot.c:__do_suspend(). 
>> Canonicalization is done both in Dom-0 and in the guest itself. Dom-0 
>> attempts to do as much of it as it can but as I've said before, it 
>> cannot do all of it.
>
> Anthony,
> Thank you for your reply.
> In linux-2.6-sparse/drivers/core/reboot.c:__do_suspend(), we see 
> store_mfn and console_mfn being canonicalized before the guest-OS goes 
> to sleep (as done in "xm save"). But before this canonicalization took 
> place the python layer writes the store_mfn and console_mfn into the 
> save-file (in the file's header area).

Yes, although this strictly isn't necessary.

> Does this mean the store_mfn and console_mfn values present in the 
> header of the file are re-written at a later part of the file ?
>
> Other than the store & console mfn's are there any other parameters 
> canoicalized BY the guest OS during "xm save" ?

Not currently, although, as Keir pointed out, you still have to contend 
with the fact that a guest may have a cached PFN somewhere (for 
instance, because it's in the process of updating a page table).

Regards,

Anthony Liguori

> thanks.
>
>
>>
>>> Also, given that Dom-0 can access the page tables and other 
>>> structures of the deadlocked guest,
>>> can one of you be able to tell me what changes I need to do to 
>>> xm_linux_save( ) (and other related functions) to save the state of 
>>> the deadlocked guest without doing any handshake with the guest OS ?
>>
>> If you want to attempt to futz with the state of a guest while it's 
>> running without the guest cooperating, your best bet is to do as Keir 
>> suggested and pause the domain, make your changes, and then unpause.
>>
>> Regards,
>>
>> Anthony Liguori
>>
>>>
>>> thanks!
>>> - T
>>>
>>>
>>>> If the guest isn't responsive when you do a save, then it will 
>>>> never canonicalize itself and there is no way to restore the domain.
>>>>
>>>> Regards,
>>>>
>>>> Anthony Liguori
>>>>
>>>>> thanks
>>>>> TS
>>>>>
>>>>>>
>>>>>> If a suspend completes correctly, Xend will see it (another watch 
>>>>>> will fire),
>>>>>> and xc_linux_save will be free to complete the save.
>>>>>>
>>>>>> > Also, does it seem viable to clone a copy of a deadlocked guest 
>>>>>> OS in the
>>>>>> > first place?
>>>>>>
>>>>>> If you have a byte-for-byte copy of a deadlocked guest, even if 
>>>>>> you could
>>>>>> suspend it, surely it will be deadlocked when it is resumed. How 
>>>>>> do you
>>>>>> intend to break the deadlock, and how is it easier to do that 
>>>>>> from outside
>>>>>> than it is to perform deadlock detection in the guest?
>>>>>>
>>>>>> Ewan.
>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> Xen-devel mailing list
>>>>>> Xen-devel@lists.xensource.com
>>>>>> http://lists.xensource.com/xen-devel
>>>>>
>>>>> _________________________________________________________________
>>>>> Express yourself instantly with MSN Messenger! Download today - 
>>>>> it's FREE! 
>>>>> http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> Xen-devel mailing list
>>>>> Xen-devel@lists.xensource.com
>>>>> http://lists.xensource.com/xen-devel
>>>>
>>>
>>> _________________________________________________________________
>>> Don’t just search. Find. Check out the new MSN Search! 
>>> http://search.msn.click-url.com/go/onm00200636ave/direct/01/
>>>
>>
>
> _________________________________________________________________
> Don’t just search. Find. Check out the new MSN Search! 
> http://search.msn.click-url.com/go/onm00200636ave/direct/01/
>