Re: [PATCH] powerpc/booke: Eliminate rfi from exception entry path.

On Tue, 2012-07-10 at 19:47 -0500, Scott Wood wrote:

On 07/10/2012 07:44 PM, Alexander Graf wrote:

quoted

On 11.07.2012, at 02:34, Scott Wood wrote:

quoted

+#ifdef CONFIG_BOOKE
+	/*
+	 * We're not changing address space on Book E, and the extra rfi
+	 * can hurt when virtualized without hardware support -- whereas
+	 * mtmsr can be paravirtualized.

We can always paravirtualize RFI as well if it makes sense.

I'm not sure that's possible.  We thought about it a while back, but
IIRC the difficulty was not leaving a register clobbered.

Besides mtmsr is slow on real HW as well. Also paravirt as done today
for complex instructions like mtmsr is racy :-) (I already had a chat
about that with Alex a while back, we might want to re-consider what
kind of fix can be done at some point).

Cheers,
Ben.