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Commit b48bbb82 authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
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powerpc/64s: Don't unbalance the return branch predictor in __replay_interrupt() 



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: default avatarGautham R. Shenoy <ego@linux.vnet.ibm.com>
Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent a9af97aa

arch/powerpc/kernel/exceptions-64s.S

+7 −1
Original line number Original line Diff line number Diff line
@@ -1639,6 +1639,10 @@ doorbell_super_common_msgclr: 
 * Note: While MSR:EE is off, we need to make sure that _MSR

 * 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

 * in the generated frame has EE set to 1 or the exception

 * handler will not properly re-enable them.

 * 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)

_GLOBAL(__replay_interrupt)

	/* We are going to jump to the exception common code which

	/* We are going to jump to the exception common code which
@@ -1646,7 +1650,7 @@ _GLOBAL(__replay_interrupt) 
	 * we don't give a damn about, so we don't bother storing them.

	 * we don't give a damn about, so we don't bother storing them.

	 */

	 */

	mfmsr	r12

	mfmsr	r12

	mflr	r11

	LOAD_REG_ADDR(r11, .L__replay_interrupt_return)

	mfcr	r9

	mfcr	r9

	ori	r12,r12,MSR_EE

	ori	r12,r12,MSR_EE

	cmpwi	r3,0x900

	cmpwi	r3,0x900
@@ -1664,4 +1668,6 @@ FTR_SECTION_ELSE 
	cmpwi	r3,0xa00

	cmpwi	r3,0xa00

	beq	doorbell_super_common_msgclr

	beq	doorbell_super_common_msgclr

ALT_FTR_SECTION_END_IFSET(CPU_FTR_HVMODE)

ALT_FTR_SECTION_END_IFSET(CPU_FTR_HVMODE)

.L__replay_interrupt_return:

	blr

	blr