From ea678ac627e01daf5b4f1da24bf1d0c500e10898 Mon Sep 17 00:00:00 2001 From: "Naveen N. Rao" Date: Thu, 19 Apr 2018 12:34:00 +0530 Subject: [PATCH] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths We have some C code that we call into from real mode where we cannot take any exceptions. Though the C functions themselves are mostly safe, if these functions are traced, there is a possibility that we may take an exception. For instance, in certain conditions, the ftrace code uses WARN(), which uses a 'trap' to do its job. For such scenarios, introduce a new field in paca 'ftrace_enabled', which is checked on ftrace entry before continuing. This field can then be set to zero to disable/pause ftrace, and set to a non-zero value to resume ftrace. Signed-off-by: Naveen N. Rao Signed-off-by: Michael Ellerman --- arch/powerpc/include/asm/paca.h | 1 + arch/powerpc/kernel/asm-offsets.c | 1 + arch/powerpc/kernel/setup_64.c | 3 +++ arch/powerpc/kernel/trace/ftrace_64_mprofile.S | 14 ++++++++++++++ arch/powerpc/kernel/trace/ftrace_64_pg.S | 4 ++++ 5 files changed, 23 insertions(+) diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h index 4185f1c..163f13f 100644 --- a/arch/powerpc/include/asm/paca.h +++ b/arch/powerpc/include/asm/paca.h @@ -223,6 +223,7 @@ struct paca_struct { u8 hmi_event_available; /* HMI event is available */ u8 hmi_p9_special_emu; /* HMI P9 special emulation */ #endif + u8 ftrace_enabled; /* Hard disable ftrace */ /* Stuff for accurate time accounting */ struct cpu_accounting_data accounting; diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c index 6bee65f..262c44a 100644 --- a/arch/powerpc/kernel/asm-offsets.c +++ b/arch/powerpc/kernel/asm-offsets.c @@ -180,6 +180,7 @@ int main(void) OFFSET(PACAKMSR, paca_struct, kernel_msr); OFFSET(PACAIRQSOFTMASK, paca_struct, irq_soft_mask); OFFSET(PACAIRQHAPPENED, paca_struct, irq_happened); + OFFSET(PACA_FTRACE_ENABLED, paca_struct, ftrace_enabled); #ifdef CONFIG_PPC_BOOK3S OFFSET(PACACONTEXTID, paca_struct, mm_ctx_id); #ifdef CONFIG_PPC_MM_SLICES diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c index b78f142..3131360 100644 --- a/arch/powerpc/kernel/setup_64.c +++ b/arch/powerpc/kernel/setup_64.c @@ -252,6 +252,9 @@ static void cpu_ready_for_interrupts(void) /* Set IR and DR in PACA MSR */ get_paca()->kernel_msr = MSR_KERNEL; + + /* We are now ok to enable ftrace */ + get_paca()->ftrace_enabled = 1; } unsigned long spr_default_dscr = 0; diff --git a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S index 3f3e818..ae1cbe7 100644 --- a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S +++ b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S @@ -47,6 +47,12 @@ _GLOBAL(ftrace_caller) /* Save all gprs to pt_regs */ SAVE_GPR(0, r1) SAVE_10GPRS(2, r1) + + /* Ok to continue? */ + lbz r3, PACA_FTRACE_ENABLED(r13) + cmpdi r3, 0 + beq ftrace_no_trace + SAVE_10GPRS(12, r1) SAVE_10GPRS(22, r1) @@ -168,6 +174,14 @@ _GLOBAL(ftrace_graph_stub) _GLOBAL(ftrace_stub) blr +ftrace_no_trace: + mflr r3 + mtctr r3 + REST_GPR(3, r1) + addi r1, r1, SWITCH_FRAME_SIZE + mtlr r0 + bctr + #ifdef CONFIG_LIVEPATCH /* * This function runs in the mcount context, between two functions. As diff --git a/arch/powerpc/kernel/trace/ftrace_64_pg.S b/arch/powerpc/kernel/trace/ftrace_64_pg.S index f095358..b7ba51a 100644 --- a/arch/powerpc/kernel/trace/ftrace_64_pg.S +++ b/arch/powerpc/kernel/trace/ftrace_64_pg.S @@ -16,6 +16,10 @@ #ifdef CONFIG_DYNAMIC_FTRACE _GLOBAL_TOC(ftrace_caller) + lbz r3, PACA_FTRACE_ENABLED(r13) + cmpdi r3, 0 + beqlr + /* Taken from output of objdump from lib64/glibc */ mflr r3 ld r11, 0(r1) -- 2.7.4