Re: [PATCH 2/4] powerpc/kuap: Avoid useless jump_label on empty function
From: "Nicholas Piggin" <npiggin@gmail.com>
Date: 2023-06-06 09:12:27
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On Mon Jun 5, 2023 at 9:04 PM AEST, Christophe Leroy wrote:
Disassembly of interrupt_enter_prepare() shows a pointless nop before the mftb c000abf0 <interrupt_enter_prepare>: c000abf0: 81 23 00 84 lwz r9,132(r3) c000abf4: 71 29 40 00 andi. r9,r9,16384 c000abf8: 41 82 00 28 beq- c000ac20 <interrupt_enter_prepare+0x30> c000abfc: ===> 60 00 00 00 nop <==== c000ac00: 7d 0c 42 e6 mftb r8 c000ac04: 80 e2 00 08 lwz r7,8(r2) c000ac08: 81 22 00 28 lwz r9,40(r2) c000ac0c: 91 02 00 24 stw r8,36(r2) c000ac10: 7d 29 38 50 subf r9,r9,r7 c000ac14: 7d 29 42 14 add r9,r9,r8 c000ac18: 91 22 00 08 stw r9,8(r2) c000ac1c: 4e 80 00 20 blr c000ac20: 60 00 00 00 nop c000ac24: 7d 5a c2 a6 mfmd_ap r10 c000ac28: 3d 20 de 00 lis r9,-8704 c000ac2c: 91 43 00 b0 stw r10,176(r3) c000ac30: 7d 3a c3 a6 mtspr 794,r9 c000ac34: 4e 80 00 20 blr That comes from the call to kuap_loc(), allthough __kuap_lock() is an empty function on the 8xx. To avoid that, only perform kuap_is_disabled() check when there is something to do with __kuap_lock(). Do the same with __kuap_save_and_lock() and __kuap_get_and_assert_locked().
Too bad static branch nops can't be eliminated.
quoted hunk ↗ jump to hunk
diff --git a/arch/powerpc/include/asm/book3s/64/kup.h b/arch/powerpc/include/asm/book3s/64/kup.h index 54cf46808157..1b0215ff3710 100644 --- a/arch/powerpc/include/asm/book3s/64/kup.h +++ b/arch/powerpc/include/asm/book3s/64/kup.h@@ -297,15 +297,7 @@ static inline unsigned long __kuap_get_and_assert_locked(void) WARN_ON_ONCE(amr != AMR_KUAP_BLOCKED); return amr; } - -/* Do nothing, book3s/64 does that in ASM */ -static inline void __kuap_lock(void) -{ -} - -static inline void __kuap_save_and_lock(struct pt_regs *regs) -{ -} +#define __kuap_get_and_assert_locked __kuap_get_and_assert_locked
Maybe leave in /* __kuap_lock notrequired, book3s/64 does that in ASM */ ? Seems okay though Reviewed-by: Nicholas Piggin <npiggin@gmail.com> Thanks, Nick