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

[Santosh Jodh <Santosh.Jodh@xxxxxxxxxx>]

> -----Original Message-----
> From: Keir Fraser [mailto:keir.xen@xxxxxxxxx]
> Sent: Friday, August 31, 2012 7:01 PM
> To: Sander Eikelenboom; Santosh Jodh
> Cc: wei.wang2@xxxxxxx; xen-devel@xxxxxxxxxxxxx
> Subject: Re: [Xen-devel] Using debug-key 'o: Dump IOMMU p2m table, locks
> up machine
> 
> On 01/09/2012 00:16, "Sander Eikelenboom" <linux@xxxxxxxxxxxxxx> 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.

Why does'nt that vCPU get scheduled on some other pCPU? Is there  a way to 
yield the CPU from the key handler?

> 
> 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. :)

It is not a generically useful command - its usefulness is in the same category 
as dumping the MMU table. Unfortunately, there is no way to pass arguments to 
the key handler - to say provide the VM and or starting gfn and length for a 
more selective output.

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