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Commit 49d09bf2 authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
Browse files

powerpc/64s: Optimise MSR handling in exception handling 



mtmsrd with L=1 only affects MSR_EE and MSR_RI bits, and we always
know what state those bits are, so the kernel MSR does not need to be
loaded when modifying them.

mtmsrd is often in the critical execution path, so avoiding dependency
on even L1 load is noticable. On a POWER8 this saves about 3 cycles
from the syscall path, and possibly a few from other exception returns
(not measured).

Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent 18e3f56b

arch/powerpc/kernel/entry_64.S

+9 −12
Original line number Diff line number Diff line
@@ -139,7 +139,7 @@ END_FW_FTR_SECTION_IFSET(FW_FEATURE_SPLPAR) 
#ifdef CONFIG_PPC_BOOK3E

	wrteei	1

#else

	ld	r11,PACAKMSR(r13)

	li	r11,MSR_RI

	ori	r11,r11,MSR_EE

	mtmsrd	r11,1

#endif /* CONFIG_PPC_BOOK3E */
@@ -195,7 +195,6 @@ system_call: /* label this so stack traces look sane */ 
#ifdef CONFIG_PPC_BOOK3E

	wrteei	0

#else

	ld	r10,PACAKMSR(r13)

	/*

	 * For performance reasons we clear RI the same time that we

	 * clear EE. We only need to clear RI just before we restore r13
@@ -203,8 +202,7 @@ system_call: /* label this so stack traces look sane */ 
	 * We have to be careful to restore RI if we branch anywhere from

	 * here (eg syscall_exit_work).

	 */

	li	r9,MSR_RI

	andc	r11,r10,r9

	li	r11,0

	mtmsrd	r11,1

#endif /* CONFIG_PPC_BOOK3E */
@@ -221,13 +219,12 @@ system_call: /* label this so stack traces look sane */ 
#endif

2:	addi    r3,r1,STACK_FRAME_OVERHEAD

#ifdef CONFIG_PPC_BOOK3S

	li	r10,MSR_RI

	mtmsrd	r10,1		/* Restore RI */

#endif

	bl	restore_math

#ifdef CONFIG_PPC_BOOK3S

	ld	r10,PACAKMSR(r13)

	li	r9,MSR_RI

	andc	r11,r10,r9 /* Re-clear RI */

	li	r11,0

	mtmsrd	r11,1

#endif

	ld	r8,_MSR(r1)
@@ -308,6 +305,7 @@ syscall_enosys: 
	

syscall_exit_work:

#ifdef CONFIG_PPC_BOOK3S

	li	r10,MSR_RI

	mtmsrd	r10,1		/* Restore RI */

#endif

	/* If TIF_RESTOREALL is set, don't scribble on either r3 or ccr.
@@ -354,7 +352,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR) 
#ifdef CONFIG_PPC_BOOK3E

	wrteei	1

#else

	ld	r10,PACAKMSR(r13)

	li	r10,MSR_RI

	ori	r10,r10,MSR_EE

	mtmsrd	r10,1

#endif /* CONFIG_PPC_BOOK3E */
@@ -619,7 +617,7 @@ _GLOBAL(ret_from_except_lite) 
#ifdef CONFIG_PPC_BOOK3E

	wrteei	0

#else

	ld	r10,PACAKMSR(r13) /* Get kernel MSR without EE */

	li	r10,MSR_RI

	mtmsrd	r10,1		  /* Update machine state */

#endif /* CONFIG_PPC_BOOK3E */
@@ -751,7 +749,7 @@ resume_kernel: 
#ifdef CONFIG_PPC_BOOK3E

	wrteei	0

#else

	ld	r10,PACAKMSR(r13) /* Get kernel MSR without EE */

	li	r10,MSR_RI

	mtmsrd	r10,1		  /* Update machine state */

#endif /* CONFIG_PPC_BOOK3E */

#endif /* CONFIG_PREEMPT */
@@ -841,8 +839,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR) 
	 * userspace and we take an exception after restoring r13,

	 * we end up corrupting the userspace r13 value.

	 */

	ld	r4,PACAKMSR(r13) /* Get kernel MSR without EE */

	andc	r4,r4,r0	 /* r0 contains MSR_RI here */

	li	r4,0

	mtmsrd	r4,1



#ifdef CONFIG_PPC_TRANSACTIONAL_MEM