Re: [PATCH] i386: improve double fault handling

[H. Peter Anvin]

Jan Beulich wrote:
> > > > Joerg Roedel <joro@xxxxxxxxxx> 23.07.08 23:43 >>>
> > On Fri, Jul 18, 2008 at 01:30:42PM +0100, Jan Beulich wrote:
> > > Make the double fault handler use CPU-specific stacks. Add some
> > > abstraction to simplify future change of other exception handlers to go
> > > through task gates.
> > What is the benefit of exception handlers going through task gates?
> > Hardware task switches are not very well supported in virtualization
> > (e.g. its has issues in KVM and is also not in Xen for a long time).
>
> The main goal is to get to a different stack. While at present this is done
> only for the double fault, I think generally NMI and MCE should also do
> so, as they may be caused by a stack access (see x86-64, which runs
> them on IST stacks), and hence continuing to run on that same stack
> may not allow the exception to be handled.

NMI, MCE and #DF are the obvious candidates.

Now, keep in mind TSSes have to be prepared per-CPU, since they get 
marked "busy" when in use, so it's a bit of a nontrivial undertaking.

	-hpa

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