Re: Using debug-key 'o: Dump IOMMU p2m table, locks up machine

[Keir Fraser <keir.xen@gmail.com>]

On 01/09/2012 00:16, "Sander Eikelenboom" <linux@eikelenboom.it> wrote:

> 
> Saturday, September 1, 2012, 12:57:45 AM, you wrote:
> 
>> The dump should complete - would be curious to see how long it takes on
>> serial console. What baudrate is the console running at?
> 
> I think for ages, this part seems only to cover a bit of the first of 3 pv
> guests which have devices passed through.
> 38400
> 
> And i wonder if the information is very valuable, gfn == mfn for every line
> ... at an increment of 1 ...
> Perhaps a uhmmm more compact way of getting the interesting data would be
> handy ?
> Or is this the intended output ?
> 
>> The code does allow processing of pending softirqs quite frequently. I am not
>> sure why you are still seeing SATA errors.
> 
> The machine is completely unresponsive in every way.

It might schedule softirqs but that won't include scheduling or running any
guest vcpus. The vcpu that happens to be running on that cpu at the time the
debug dump starts, will be stuck unrunnable until the dump completes.

Well, anyway, I don't know how useful a massive dump of the entire p2m is
going to be for debugging anyway. If investigating an IOMMU page fault, I'd
just want the info pertaining to that fault, and all the mapping information
for that IO virtual address, dumped. :)

 -- Keir

> And using it with "xl debug-keys o" is never going to work i guess, since the
> information flood is far larger than "xl dmesg" keeps ?
> 
> 
> 
>>> -----Original Message-----
>>> From: Sander Eikelenboom [mailto:linux@eikelenboom.it]
>>> Sent: Friday, August 31, 2012 3:43 PM
>>> To: Santosh Jodh
>>> Cc: wei.wang2@amd.com; xen-devel@lists.xen.org
>>> Subject: Re: Using debug-key 'o: Dump IOMMU p2m table, locks up machine
>>> 
>>> 
>>> Saturday, September 1, 2012, 12:24:32 AM, you wrote:
>>> 
>>>> Depending on how many VMs you have and the size of the IOMMU p2m
>>> table, it can take a while. It should not be infinite though.
>>> 
>>>> How many VMs do you have running?
>>> 
>>> 15
>>> 
>>>> Can you please send the serial output when you press 'o'?
>>> 
>>> Attached, to the end you will see the s-ata errors coming through while the
>>> dump still runs.
>>> This is not a complete dump, only a few minutes after which i did a hard
>>> reset.
>>> 
>>>> Santosh
>>> 
>>>>> -----Original Message-----
>>>>> From: Sander Eikelenboom [mailto:linux@eikelenboom.it]
>>>>> Sent: Friday, August 31, 2012 2:45 PM
>>>>> To: Santosh Jodh; wei.wang2@amd.com
>>>>> Cc: xen-devel@lists.xen.org
>>>>> Subject: Using debug-key 'o: Dump IOMMU p2m table, locks up machine
>>>>> 
>>>>> 
>>>>> I was trying to use the 'o' debug key to make a bug report about an "AMD-
>>> Vi:
>>>>> IO_PAGE_FAULT".
>>>>> 
>>>>> The result:
>>>>> - When using "xl debug-keys o", the machine seems in a infinite loop,
>>>>> can hardly login, eventually resulting in a kernel RCU stall and complete
>>> lockup.
>>>>> - When using serial console: I get a infinite stream of "gfn:  mfn: "
>>>>> lines, mean while on the normal console, S-ATA devices are starting to
>>> give errors.
>>>>> 
>>>>> So either option trashes the machine, other debug-keys work fine.
>>>>> 
>>>>> Machine has a 890-fx chipset and AMD phenom x6 proc.
>>>>> 
>>>>> xl dmesg with bootup and output from some other debug-keys is
>>> attached.
>>>>> 
>>>>> --
>>>>> 
>>>>> Sander
>>> 
>>> 
>>> 
>>> 
>>> --
>>> Best regards,
>>>  Sander                            mailto:linux@eikelenboom.it
> 
> 
>