Re: [PATCH 2/2] paravirt inline patching

[Andi Kleen <ak@muc.de>]

On Tue, 22 Aug 2006 16:12:32 +1000
Rusty Russell <rusty@rustcorp.com.au> wrote:


> It turns out that the most called ops, by several orders of magnitude,
> are the interrupt manipulation ops.  These are obvious candidates for
> patching, so mark them up and create infrastructure for it.
> 
> The method used is that the ops structure has a patch function, which
> is called for each place which needs to be patched: this returns a
> number of instructions (the rest are NOP-padded).
> 
> Usually we can spare a register (%eax) for the binary patched code to
> use, but in a couple of critical places in entry.S we can't: we make
> the clobbers explicit at the call site, and manually clobber the
> allowed registers in debug mode as an extra check.

Looks good to me.

> +
> +	/* Sync in case we patched this coming "sti" last. */
> +	sync_core();

I guess this needs more comments -- in particular that it is 
only safe because the other CPUs are not executing any of this
yet and preempt does synchronize anyways.

-Andi