From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 40G0dH02cpzF29s for ; Wed, 4 Apr 2018 06:12:50 +1000 (AEST) Received: from pps.filterd (m0098404.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w33KBY88101214 for ; Tue, 3 Apr 2018 16:12:48 -0400 Received: from e06smtp14.uk.ibm.com (e06smtp14.uk.ibm.com [195.75.94.110]) by mx0a-001b2d01.pphosted.com with ESMTP id 2h4fuqhs7f-1 (version=TLSv1.2 cipher=AES256-SHA256 bits=256 verify=NOT) for ; Tue, 03 Apr 2018 16:12:47 -0400 Received: from localhost by e06smtp14.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 3 Apr 2018 21:12:45 +0100 From: "Naveen N. Rao" To: Michael Ellerman , Steven Rostedt Cc: linuxppc-dev@lists.ozlabs.org, Paul Mackerras , Nicholas Piggin , Anton Blanchard , sathnaga@linux.vnet.ibm.com Subject: [PATCH v4 01/10] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths Date: Wed, 4 Apr 2018 01:42:16 +0530 In-Reply-To: References: In-Reply-To: References: Message-Id: List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 --- 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 4185f1c96125..163f13f31255 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 6bee65f3cfd3..262c44a90ea1 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 66f2b6299c40..a96ea3bab8f4 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 3f3e81852422..ae1cbe783ab6 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 f095358da96e..b7ba51a0f3b6 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) -- 2.16.2