[PATCH v5 15/22] powerpc/32: Remove verification of MSR_PR on syscall in the ASM entry

From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	npiggin@gmail.com, msuchanek@suse.de
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: [PATCH v5 15/22] powerpc/32: Remove verification of MSR_PR on syscall in the ASM entry
Date: Mon,  8 Feb 2021 15:10:34 +0000 (UTC)	[thread overview]
Message-ID: <1eddb42cb12092b1e3d72608d182c365db3da41d.1612796617.git.christophe.leroy@csgroup.eu> (raw)
In-Reply-To: <cover.1612796617.git.christophe.leroy@csgroup.eu>

system_call_exception() checks MSR_PR and BUGs if a syscall
is issued from kernel mode.

No need to handle it anymore from the ASM entry code.

null_syscall reduction 2 cycles (348 => 346 cycles)

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 arch/powerpc/kernel/entry_32.S   | 30 ------------------------------
 arch/powerpc/kernel/head_32.h    |  3 ---
 arch/powerpc/kernel/head_booke.h |  3 ---
 3 files changed, 36 deletions(-)

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index bbf7ecea6fe0..cffe58e63356 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -421,36 +421,6 @@ ret_from_kernel_thread:
 	li	r3,0
 	b	ret_from_syscall
 
-	/*
-	 * System call was called from kernel. We get here with SRR1 in r9.
-	 * Mark the exception as recoverable once we have retrieved SRR0,
-	 * trap a warning and return ENOSYS with CR[SO] set.
-	 */
-	.globl	ret_from_kernel_syscall
-ret_from_kernel_syscall:
-	mfspr	r9, SPRN_SRR0
-	mfspr	r10, SPRN_SRR1
-#if !defined(CONFIG_4xx) && !defined(CONFIG_BOOKE)
-	LOAD_REG_IMMEDIATE(r11, MSR_KERNEL & ~(MSR_IR|MSR_DR))
-	mtmsr	r11
-#endif
-
-0:	trap
-	EMIT_BUG_ENTRY 0b,__FILE__,__LINE__, BUGFLAG_WARNING
-
-	li	r3, ENOSYS
-	crset	so
-#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PERF_EVENTS)
-	mtspr	SPRN_NRI, r0
-#endif
-	mtspr	SPRN_SRR0, r9
-	mtspr	SPRN_SRR1, r10
-	rfi
-#ifdef CONFIG_40x
-	b .	/* Prevent prefetch past rfi */
-#endif
-_ASM_NOKPROBE_SYMBOL(ret_from_kernel_syscall)
-
 /*
  * Top-level page fault handling.
  * This is in assembler because if do_page_fault tells us that
diff --git a/arch/powerpc/kernel/head_32.h b/arch/powerpc/kernel/head_32.h
index fea7fe00a690..282d8fd443a9 100644
--- a/arch/powerpc/kernel/head_32.h
+++ b/arch/powerpc/kernel/head_32.h
@@ -118,8 +118,6 @@
 .macro SYSCALL_ENTRY trapno
 	mfspr	r9, SPRN_SRR1
 	mfspr	r10, SPRN_SRR0
-	andi.	r11, r9, MSR_PR
-	beq-	99f
 	LOAD_REG_IMMEDIATE(r11, MSR_KERNEL)		/* can take exceptions */
 	lis	r12, 1f@h
 	ori	r12, r12, 1f@l
@@ -174,7 +172,6 @@
 3:
 #endif
 	b	transfer_to_syscall		/* jump to handler */
-99:	b	ret_from_kernel_syscall
 .endm
 
 .macro save_dar_dsisr_on_stack reg1, reg2, sp
diff --git a/arch/powerpc/kernel/head_booke.h b/arch/powerpc/kernel/head_booke.h
index db931f1167aa..bfbd240cc8a2 100644
--- a/arch/powerpc/kernel/head_booke.h
+++ b/arch/powerpc/kernel/head_booke.h
@@ -106,10 +106,8 @@ ALT_FTR_SECTION_END_IFSET(CPU_FTR_EMB_HV)
 #endif
 	mfspr	r9, SPRN_SRR1
 	BOOKE_CLEAR_BTB(r11)
-	andi.	r11, r9, MSR_PR
 	lwz	r11, TASK_STACK - THREAD(r10)
 	rlwinm	r12,r12,0,4,2	/* Clear SO bit in CR */
-	beq-	99f
 	ALLOC_STACK_FRAME(r11, THREAD_SIZE - INT_FRAME_SIZE)
 	stw	r12, _CCR(r11)		/* save various registers */
 	mflr	r12
@@ -155,7 +153,6 @@ ALT_FTR_SECTION_END_IFSET(CPU_FTR_EMB_HV)
 
 3:
 	b	transfer_to_syscall	/* jump to handler */
-99:	b	ret_from_kernel_syscall
 .endm
 
 /* To handle the additional exception priority levels on 40x and Book-E
-- 
2.25.0

