[PATCH v2 13/17] powerpc/32: implement fast entry for syscalls on non BOOKE

From: Christophe Leroy
Date: Fri Mar 29 2019 - 12:39:11 EST

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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@xxxxxx>
---
arch/powerpc/kernel/entry_32.S | 32 ++++++++++++++++
arch/powerpc/kernel/head_32.S | 3 +-
arch/powerpc/kernel/head_32.h | 85 ++++++++++++++++++++++++++++++++++++++++--
arch/powerpc/kernel/head_40x.S | 3 +-
arch/powerpc/kernel/head_8xx.S | 3 +-
5 files changed, 116 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 00481116391d..71a101600428 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -335,6 +335,35 @@ stack_ovf:
SYNC
RFI

+#ifndef CONFIG_BOOKE /* to be removed once BOOKE uses fast syscall entry */
+#ifdef CONFIG_TRACE_IRQFLAGS
+trace_syscall_entry_irq_off:
+ /*
+ * Syscall shouldn't happen while interrupts are disabled,
+ * so let's do a warning here.
+ */
+0: trap
+ EMIT_BUG_ENTRY 0b,__FILE__,__LINE__, BUGFLAG_WARNING
+ bl trace_hardirqs_on
+
+ /* Now enable for real */
+ LOAD_MSR_KERNEL(r10, MSR_KERNEL | MSR_EE)
+ mtmsr r10
+
+ REST_GPR(0, r1)
+ REST_4GPRS(3, r1)
+ REST_2GPRS(7, r1)
+ b DoSyscall
+#endif /* CONFIG_TRACE_IRQFLAGS */
+
+ .globl transfer_to_syscall
+transfer_to_syscall:
+#ifdef CONFIG_TRACE_IRQFLAGS
+ andi. r12,r9,MSR_EE
+ beq- trace_syscall_entry_irq_off
+#endif /* CONFIG_TRACE_IRQFLAGS */
+#endif /* !CONFIG_BOOKE */
+
/*
* Handle a system call.
*/
@@ -346,9 +375,11 @@ _GLOBAL(DoSyscall)
stw r3,ORIG_GPR3(r1)
li r12,0
stw r12,RESULT(r1)
+#ifdef CONFIG_BOOKE /* to be removed once BOOKE uses fast syscall entry */
lwz r11,_CCR(r1) /* Clear SO bit in CR */
rlwinm r11,r11,0,4,2
stw r11,_CCR(r1)
+#endif
#ifdef CONFIG_TRACE_IRQFLAGS
/* Make sure interrupts are enabled */
mfmsr r11
@@ -1207,6 +1238,7 @@ load_dbcr0:

.section .bss
.align 4
+ .global global_dbcr0
global_dbcr0:
.space 8*NR_CPUS
.previous
diff --git a/arch/powerpc/kernel/head_32.S b/arch/powerpc/kernel/head_32.S
index 983480f9547b..7309f52002c2 100644
--- a/arch/powerpc/kernel/head_32.S
+++ b/arch/powerpc/kernel/head_32.S
@@ -366,8 +366,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_FPU_UNAVAILABLE)
. = 0xc00
DO_KVM 0xc00
SystemCall:
- EXCEPTION_PROLOG
- EXC_XFER_SYS(0xc00, DoSyscall)
+ SYSCALL_ENTRY 0xc00

/* Single step - not used on 601 */
EXCEPTION(0xd00, SingleStep, single_step_exception, EXC_XFER_STD)
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 @@
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__ */
diff --git a/arch/powerpc/kernel/head_40x.S b/arch/powerpc/kernel/head_40x.S
index b68de183faf1..e115248edda1 100644
--- a/arch/powerpc/kernel/head_40x.S
+++ b/arch/powerpc/kernel/head_40x.S
@@ -348,8 +348,7 @@ _ENTRY(saved_ksp_limit)

/* 0x0C00 - System Call Exception */
START_EXCEPTION(0x0C00, SystemCall)
- EXCEPTION_PROLOG
- EXC_XFER_SYS(0xc00, DoSyscall)
+ SYSCALL_ENTRY 0xc00

EXCEPTION(0x0D00, Trap_0D, unknown_exception, EXC_XFER_STD)
EXCEPTION(0x0E00, Trap_0E, unknown_exception, EXC_XFER_STD)
diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
index 4ebcdfdae920..a5826defad1f 100644
--- a/arch/powerpc/kernel/head_8xx.S
+++ b/arch/powerpc/kernel/head_8xx.S
@@ -185,8 +185,7 @@ Alignment:
/* System call */
. = 0xc00
SystemCall:
- EXCEPTION_PROLOG
- EXC_XFER_SYS(0xc00, DoSyscall)
+ SYSCALL_ENTRY 0xc00

/* Single step - not used on 601 */
EXCEPTION(0xd00, SingleStep, single_step_exception, EXC_XFER_STD)
--
2.13.3

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