powerpc/32: implement fast entry for syscalls on non BOOKE

This patch implements a fast entry for syscalls.

Syscalls don't have to preserve non volatile registers except LR.

This patch then implement a fast entry for syscalls, where
volatile registers get clobbered.

As this entry is dedicated to syscall it always sets MSR_EE
and warns in case MSR_EE was previously off

It also assumes that the call is always from user, system calls are
unexpected from kernel.

The overall series improves null_syscall selftest by 12,5% on an 83xx
and by 17% on a 8xx.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 81 insertions, 4 deletions

diff --git a/arch/powerpc/kernel/head_32.h b/arch/powerpc/kernel/head_32.h
index 14cb0af2f494..4a692553651f 100644
--- a/arch/powerpc/kernel/head_32.h
+++ b/arch/powerpc/kernel/head_32.h
@@ -73,6 +73,87 @@
 	SAVE_2GPRS(7, r11)
 .endm
 
+.macro SYSCALL_ENTRY trapno
+	mfspr	r12,SPRN_SPRG_THREAD
+	mfcr	r10
+	lwz	r11,TASK_STACK-THREAD(r12)
+	mflr	r9
+	addi	r11,r11,THREAD_SIZE - INT_FRAME_SIZE
+	rlwinm	r10,r10,0,4,2	/* Clear SO bit in CR */
+	tophys(r11,r11)
+	stw	r10,_CCR(r11)		/* save registers */
+	mfspr	r10,SPRN_SRR0
+	stw	r9,_LINK(r11)
+	mfspr	r9,SPRN_SRR1
+	stw	r1,GPR1(r11)
+	stw	r1,0(r11)
+	tovirt(r1,r11)			/* set new kernel sp */
+	stw	r10,_NIP(r11)
+#ifdef CONFIG_40x
+	rlwinm	r9,r9,0,14,12		/* clear MSR_WE (necessary?) */
+#else
+	LOAD_MSR_KERNEL(r10, MSR_KERNEL & ~(MSR_IR|MSR_DR)) /* can take exceptions */
+	MTMSRD(r10)			/* (except for mach check in rtas) */
+#endif
+	lis	r10,STACK_FRAME_REGS_MARKER@ha /* exception frame marker */
+	stw	r2,GPR2(r11)
+	addi	r10,r10,STACK_FRAME_REGS_MARKER@l
+	stw	r9,_MSR(r11)
+	li	r2, \trapno + 1
+	stw	r10,8(r11)
+	stw	r2,_TRAP(r11)
+	SAVE_GPR(0, r11)
+	SAVE_4GPRS(3, r11)
+	SAVE_2GPRS(7, r11)
+	addi	r11,r1,STACK_FRAME_OVERHEAD
+	addi	r2,r12,-THREAD
+	stw	r11,PT_REGS(r12)
+#if defined(CONFIG_40x)
+	/* Check to see if the dbcr0 register is set up to debug.  Use the
+	   internal debug mode bit to do this. */
+	lwz	r12,THREAD_DBCR0(r12)
+	andis.	r12,r12,DBCR0_IDM@h
+#endif
+	ACCOUNT_CPU_USER_ENTRY(r2, r11, r12)
+#if defined(CONFIG_40x)
+	beq+	3f
+	/* From user and task is ptraced - load up global dbcr0 */
+	li	r12,-1			/* clear all pending debug events */
+	mtspr	SPRN_DBSR,r12
+	lis	r11,global_dbcr0@ha
+	tophys(r11,r11)
+	addi	r11,r11,global_dbcr0@l
+	lwz	r12,0(r11)
+	mtspr	SPRN_DBCR0,r12
+	lwz	r12,4(r11)
+	addi	r12,r12,-1
+	stw	r12,4(r11)
+#endif
+
+3:
+	tovirt(r2, r2)			/* set r2 to current */
+	lis	r11, transfer_to_syscall@h
+	ori	r11, r11, transfer_to_syscall@l
+#ifdef CONFIG_TRACE_IRQFLAGS
+	/*
+	 * If MSR is changing we need to keep interrupts disabled at this point
+	 * otherwise we might risk taking an interrupt before we tell lockdep
+	 * they are enabled.
+	 */
+	LOAD_MSR_KERNEL(r10, MSR_KERNEL)
+	rlwimi	r10, r9, 0, MSR_EE
+#else
+	LOAD_MSR_KERNEL(r10, MSR_KERNEL | MSR_EE)
+#endif
+#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PERF_EVENTS)
+	mtspr	SPRN_NRI, r0
+#endif
+	mtspr	SPRN_SRR1,r10
+	mtspr	SPRN_SRR0,r11
+	SYNC
+	RFI				/* jump to handler, enable MMU */
+.endm
+
 /*
  * Note: code which follows this uses cr0.eq (set if from kernel),
  * r11, r12 (SRR0), and r9 (SRR1).
@@ -119,8 +200,4 @@ label:
 	EXC_XFER_TEMPLATE(hdlr, n+1, MSR_KERNEL, transfer_to_handler, \
 			  ret_from_except)
 
-#define EXC_XFER_SYS(n, hdlr)		\
-	EXC_XFER_TEMPLATE(hdlr, n+1, MSR_KERNEL | MSR_EE, transfer_to_handler, \
-			  ret_from_except)
-
 #endif /* __HEAD_32_H__ */