Re: Implement generic double fault generation mechanism

[Gleb Natapov <gleb@redhat.com>]

On Mon, May 11, 2009 at 09:04:52AM +0800, Dong, Eddie wrote:
> 
> > There is not point referring to current code. Current code does not
> > handle serial exceptions properly. So fix it in your patch otherwise I
> > propose to use my patch that fixes current code
> > (http://patchwork.kernel.org/patch/21829/).
> > 
> 
> I would like Avi to decide. As comments to the difference of 2 patches, my undrestanding is that I am addressing the problem base on SDM 5-4 with the answer to serial injection as first in first service. Your patch doesn;t solve generic double fault case for example exception 11 on 11, or GP on GP which needs to be converted to #DF per SDM, rather you only handle the case the secondary exception is PF,  and servicing PF.
> 
There is nothing to decide really. I prefer your patch with serial
exception handling fixed. If you'll not do it I'll do it.

> I can check with internal architecture to see what does "handle exceptions serially" mean in really. For me serial means first in first out, and thus we should remain 1st exception.
> 
There is a table 5.2 that defines an order between some events.  The table
is not complete, I don't see #DE there for instance.  But consider
this case: #DE (or #NP) happens while exception stack is paged out so
#PF happens next. #PF is handled by TSS gate so it uses its own stack
and it fixes exception stack in its handler. If we drop #PF because #DE
is already waiting we will keep trying to inject #DE indefinitely. The
result is hanging QEMU process eating 100% cpu time. If we replace #DE
with #PF on the other hand then #PF handler will fix exception stack
instruction that caused #DE will be re-executed, #DE regenerated and
handled properly. So which scenario do you prefer?

WFIW bochs/qemu replace old exception with a new one.

--
			Gleb.