[PATCH 05/13] powerpc/64s: interrupt replay balance the return branch predictor
From: Nicholas Piggin <npiggin@gmail.com>
Date: 2017-06-13 13:06:27
Subsystem:
linux for powerpc (32-bit and 64-bit), the rest · Maintainers:
Madhavan Srinivasan, Linus Torvalds
The __replay_interrupt code is branched to with bl, but the caller is returned to directly with rfid from the interrupt. Instead, rfid to a stub that returns to the caller with blr, which should keep the return branch predictor balanced. Reviewed-by: Gautham R. Shenoy <redacted> Signed-off-by: Nicholas Piggin <npiggin@gmail.com> --- arch/powerpc/kernel/exceptions-64s.S | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index a04ee0d7f88e..31a9114860c4 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S@@ -1579,6 +1579,10 @@ doorbell_super_common_msgclr: * Note: While MSR:EE is off, we need to make sure that _MSR * in the generated frame has EE set to 1 or the exception * handler will not properly re-enable them. + * + * Note that we don't specify LR as the NIP (return address) for + * the interrupt because that would unbalance the return branch + * predictor. */ _GLOBAL(__replay_interrupt) /* We are going to jump to the exception common code which
@@ -1586,7 +1590,7 @@ _GLOBAL(__replay_interrupt) * we don't give a damn about, so we don't bother storing them. */ mfmsr r12 - mflr r11 + LOAD_REG_ADDR(r11, .L__replay_interrupt_return) mfcr r9 ori r12,r12,MSR_EE cmpwi r3,0x900
@@ -1604,4 +1608,6 @@ FTR_SECTION_ELSE cmpwi r3,0xa00 beq doorbell_super_common_msgclr ALT_FTR_SECTION_END_IFSET(CPU_FTR_HVMODE) +.L__replay_interrupt_return: blr +
--
2.11.0