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    Subject[PATCH v3 13/16] powerpc/32: implement fast entry for syscalls on non BOOKE
    Date
    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>
    ---
    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 0c555f9f1543..184cc1de2f37 100644
    --- a/arch/powerpc/kernel/entry_32.S
    +++ b/arch/powerpc/kernel/entry_32.S
    @@ -342,6 +342,35 @@ 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.
    */
    @@ -353,9 +382,11 @@ _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
    @@ -1219,6 +1250,7 @@ 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 2404c39373d3..f1da8fef726a 100644
    --- a/arch/powerpc/kernel/head_32.S
    +++ b/arch/powerpc/kernel/head_32.S
    @@ -370,8 +370,7 @@ 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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