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

From: Scott Wood <[email-masked]>
Date: Tue, 10 Jul 2012 19:34:54 -0500

Unlike classic, we don't really need the MSR change to be atomic with the
branch.  This eliminates a trap as a KVM guest (in the absence of
hardware hypervisor extensions), where mtmsr is paravirtualized but rfi
is not.  For a virtualized guest without any paravirtualization, this
eliminates an additional two traps (SRR0/1).

Signed-off-by: Scott Wood <[email-masked]>
---
 arch/powerpc/kernel/entry_32.S |   16 ++++++++++++++++
 1 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index ba3aeb4..6bb637c 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -193,6 +193,9 @@ transfer_to_handler_cont:
 	lwz	r11,0(r9)		/* virtual address of handler */
 	lwz	r9,4(r9)		/* where to go when done */
 #ifdef CONFIG_TRACE_IRQFLAGS
+#ifdef CONFIG_BOOKE
+	mtmsr	r10
+#else
 	lis	r12,reenable_mmu@h
 	ori	r12,r12,reenable_mmu@l
 	mtspr	SPRN_SRR0,r12
@@ -201,6 +204,7 @@ transfer_to_handler_cont:
 	RFI
 reenable_mmu:				/* re-enable mmu so we can */
 	mfmsr	r10
+#endif /* !CONFIG_BOOKE */
 	lwz	r12,_MSR(r1)
 	xor	r10,r10,r12
 	andi.	r10,r10,MSR_EE		/* Did EE change? */
@@ -247,11 +251,23 @@ reenable_mmu:				/* re-enable mmu so we can */
 	mtlr	r9
 	bctr				/* jump to handler */
 #else /* CONFIG_TRACE_IRQFLAGS */
+#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.
+	 */
+	mtmsr	r10
+	mtctr	r11
+	mtlr	r9
+	bctr
+#else
 	mtspr	SPRN_SRR0,r11
 	mtspr	SPRN_SRR1,r10
 	mtlr	r9
 	SYNC
 	RFI				/* jump to handler, enable MMU */
+#endif /* !CONFIG_BOOKE */
 #endif /* CONFIG_TRACE_IRQFLAGS */
 
 #if defined (CONFIG_6xx) || defined(CONFIG_E500)
-- 
1.7.5.4