[PATCH v2 14/17] powerpc/32: implement fast entry for syscalls on BOOKE

From: Christophe Leroy
Date: Fri Mar 29 2019 - 12:38:44 EST

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.

Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
---
arch/powerpc/kernel/entry_32.S | 7 ---
arch/powerpc/kernel/head_44x.S | 3 +-
arch/powerpc/kernel/head_booke.h | 103 +++++++++++++++++++++++++++++++++--
arch/powerpc/kernel/head_fsl_booke.S | 3 +-
4 files changed, 100 insertions(+), 16 deletions(-)

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 71a101600428..5f52a71c2838 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -335,7 +335,6 @@ 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:
/*
@@ -362,7 +361,6 @@ transfer_to_syscall:
andi. r12,r9,MSR_EE
beq- trace_syscall_entry_irq_off
#endif /* CONFIG_TRACE_IRQFLAGS */
-#endif /* !CONFIG_BOOKE */

/*
* Handle a system call.
@@ -375,11 +373,6 @@ _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
diff --git a/arch/powerpc/kernel/head_44x.S b/arch/powerpc/kernel/head_44x.S
index e06cb1c84951..7d73c7e39afe 100644
--- a/arch/powerpc/kernel/head_44x.S
+++ b/arch/powerpc/kernel/head_44x.S
@@ -282,8 +282,7 @@ interrupt_base:
#endif
/* System Call Interrupt */
START_EXCEPTION(SystemCall)
- NORMAL_EXCEPTION_PROLOG(BOOKE_INTERRUPT_SYSCALL)
- EXC_XFER_SYS(0x0c00, DoSyscall)
+ SYSCALL_ENTRY 0xc00 BOOKE_INTERRUPT_SYSCALL

/* Auxiliary Processor Unavailable Interrupt */
EXCEPTION(0x2020, BOOKE_INTERRUPT_AP_UNAVAIL, \
diff --git a/arch/powerpc/kernel/head_booke.h b/arch/powerpc/kernel/head_booke.h
index 56dd1341eb3d..bfeb469e8106 100644
--- a/arch/powerpc/kernel/head_booke.h
+++ b/arch/powerpc/kernel/head_booke.h
@@ -6,6 +6,8 @@
#include <asm/kvm_asm.h>
#include <asm/kvm_booke_hv_asm.h>

+#ifdef __ASSEMBLY__
+
/*
* Macros used for common Book-e exception handling
*/
@@ -81,6 +83,101 @@ END_BTB_FLUSH_SECTION
SAVE_4GPRS(3, r11); \
SAVE_2GPRS(7, r11)

+.macro SYSCALL_ENTRY trapno intno
+ mfspr r10, SPRN_SPRG_THREAD
+#ifdef CONFIG_KVM_BOOKE_HV
+BEGIN_FTR_SECTION
+ mtspr SPRN_SPRG_WSCRATCH0, r10
+ stw r11, THREAD_NORMSAVE(0)(r10)
+ stw r13, THREAD_NORMSAVE(2)(r10)
+ mfcr r13 /* save CR in r13 for now */
+ mfspr r11, SPRN_SRR1
+ mtocrf 0x80, r11 /* check MSR[GS] without clobbering reg */
+ bf 3, 1975f
+ b kvmppc_handler_BOOKE_INTERRUPT_\intno\()_SPRN_SRR1
+1975:
+ mr r12, r13
+ lwz r13, THREAD_NORMSAVE(2)(r10)
+FTR_SECTION_ELSE
+#endif
+ mfcr r12
+#ifdef CONFIG_KVM_BOOKE_HV
+ALT_FTR_SECTION_END_IFSET(CPU_FTR_EMB_HV)
+#endif
+ BOOKE_CLEAR_BTB(r11)
+ lwz r11, TASK_STACK - THREAD(r10)
+ rlwinm r12,r12,0,4,2 /* Clear SO bit in CR */
+ ALLOC_STACK_FRAME(r11, THREAD_SIZE - INT_FRAME_SIZE)
+ stw r12, _CCR(r11) /* save various registers */
+ mflr r12
+ stw r12,_LINK(r11)
+ mfspr r12,SPRN_SRR0
+ stw r1, GPR1(r11)
+ mfspr r9,SPRN_SRR1
+ stw r1, 0(r11)
+ mr r1, r11
+ stw r12,_NIP(r11)
+ rlwinm r9,r9,0,14,12 /* clear MSR_WE (necessary?) */
+ lis r12, STACK_FRAME_REGS_MARKER@ha /* exception frame marker */
+ stw r2,GPR2(r11)
+ addi r12, r12, STACK_FRAME_REGS_MARKER@l
+ stw r9,_MSR(r11)
+ li r2, \trapno + 1
+ stw r12, 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,r10,-THREAD
+ stw r11,PT_REGS(r10)
+ /* 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(r10)
+ andis. r12,r12,DBCR0_IDM@h
+ ACCOUNT_CPU_USER_ENTRY(r2, r11, r12)
+ 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
+#ifdef CONFIG_SMP
+ lwz r9,TASK_CPU(r2)
+ slwi r9,r9,3
+ add r11,r11,r9
+#endif
+ lwz r12,0(r11)
+ mtspr SPRN_DBCR0,r12
+ lwz r12,4(r11)
+ addi r12,r12,-1
+ stw r12,4(r11)
+
+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.
+ */
+ lis r10, MSR_KERNEL@h
+ ori r10, r10, MSR_KERNEL@l
+ rlwimi r10, r9, 0, MSR_EE
+#else
+ lis r10, (MSR_KERNEL | MSR_EE)@h
+ ori r10, r10, (MSR_KERNEL | MSR_EE)@l
+#endif
+ mtspr SPRN_SRR1,r10
+ mtspr SPRN_SRR0,r11
+ SYNC
+ RFI /* jump to handler, enable MMU */
+.endm
+
/* To handle the additional exception priority levels on 40x and Book-E
* processors we allocate a stack per additional priority level.
*
@@ -245,10 +342,6 @@ END_BTB_FLUSH_SECTION
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)
-
/* Check for a single step debug exception while in an exception
* handler before state has been saved. This is to catch the case
* where an instruction that we are trying to single step causes
@@ -418,7 +511,7 @@ END_BTB_FLUSH_SECTION
1: addi r3,r1,STACK_FRAME_OVERHEAD; \
EXC_XFER_STD(0x800, kernel_fp_unavailable_exception)

-#ifndef __ASSEMBLY__
+#else /* __ASSEMBLY__ */
struct exception_regs {
unsigned long mas0;
unsigned long mas1;
diff --git a/arch/powerpc/kernel/head_fsl_booke.S b/arch/powerpc/kernel/head_fsl_booke.S
index b351851dc73d..a757be4f1cb5 100644
--- a/arch/powerpc/kernel/head_fsl_booke.S
+++ b/arch/powerpc/kernel/head_fsl_booke.S
@@ -410,8 +410,7 @@ interrupt_base:

/* System Call Interrupt */
START_EXCEPTION(SystemCall)
- NORMAL_EXCEPTION_PROLOG(SYSCALL)
- EXC_XFER_SYS(0x0c00, DoSyscall)
+ SYSCALL_ENTRY 0xc00 SYSCALL

/* Auxiliary Processor Unavailable Interrupt */
EXCEPTION(0x2900, AP_UNAVAIL, AuxillaryProcessorUnavailable, \
--
2.13.3