[PATCH 02/14] powerpc/pseries: remove cross-fixup branches in exception code

[Nicholas Piggin]

In preparation for reworking the alternate feature patching code,
remove a case of cross-fixup branching in the exception code. That
is, a branch from one alt feature section targeting another alt
feature section.

We have the following:

BEGIN_FTR_SECTION
b	do_kvm_0x502
...
do_kvm_0x502:
...
FTR_SECTION_ELSE
b	do_kvm_0x500
...
do_kvm_0x500:
...
ALT_FTR_SECTION_END_IFSET(CPU_FTR_HVMODE | CPU_FTR_ARCH_206)


BEGIN_FTR_SECTION
b	do_kvm_0x502
FTR_SECTION_ELSE
b	do_kvm_0x500
ALT_FTR_SECTION_END_IFSET(CPU_FTR_HVMODE)

This somehow manages to work today. The first branch to do_kvm_0x500 works
as expected and branches to the do_kvm_0x500 code that is moved to the
destination location. The second branch to it branches to the linked
location of the do_kvm_0x500 code. Two copies of the code are being
executed.

A subsequent patch moves the patchcode far away and discards it after
boot, so this type of branch doesn't work.

Signed-off-by: Nick Piggin <npiggin at gmail.com>
---
 arch/powerpc/kernel/exceptions-64s.S | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 4c94406..18befa5 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -257,13 +257,18 @@ hardware_interrupt_hv:
 	BEGIN_FTR_SECTION
 		_MASKABLE_EXCEPTION_PSERIES(0x502, hardware_interrupt,
 					    EXC_HV, SOFTEN_TEST_HV)
-		KVM_HANDLER(PACA_EXGEN, EXC_HV, 0x502)
 	FTR_SECTION_ELSE
 		_MASKABLE_EXCEPTION_PSERIES(0x500, hardware_interrupt,
 					    EXC_STD, SOFTEN_TEST_PR)
-		KVM_HANDLER(PACA_EXGEN, EXC_STD, 0x500)
 	ALT_FTR_SECTION_END_IFSET(CPU_FTR_HVMODE | CPU_FTR_ARCH_206)
 
+	/*
+	 * Relon code jumps to these KVM handlers too so can't put them
+	 * in the feature sections.
+	 */
+	KVM_HANDLER(PACA_EXGEN, EXC_HV, 0x502)
+	KVM_HANDLER(PACA_EXGEN, EXC_STD, 0x500)
+
 	STD_EXCEPTION_PSERIES(0x600, alignment)
 	KVM_HANDLER(PACA_EXGEN, EXC_STD, 0x600)
 
-- 
2.8.1