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 406N9X3qvpzF1sl for ; Thu, 22 Mar 2018 21:25:52 +1100 (AEDT) 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 w2MAP8in138545 for ; Thu, 22 Mar 2018 06:25:48 -0400 Received: from e06smtp11.uk.ibm.com (e06smtp11.uk.ibm.com [195.75.94.107]) by mx0a-001b2d01.pphosted.com with ESMTP id 2gv5e04hdk-1 (version=TLSv1.2 cipher=AES256-SHA256 bits=256 verify=NOT) for ; Thu, 22 Mar 2018 06:25:47 -0400 Received: from localhost by e06smtp11.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 22 Mar 2018 10:25:44 -0000 From: "Naveen N. Rao" To: Michael Ellerman , Steven Rostedt , Paul Mackerras Cc: linuxppc-dev@lists.ozlabs.org, Anton Blanchard , Nicholas Piggin , sathnaga@linux.vnet.ibm.com Subject: [PATCH v3 1/6] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths Date: Thu, 22 Mar 2018 15:55:21 +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_disabled', which is checked on ftrace entry before continuing. This field can then be set to a non-zero value to disable/pause ftrace, and reset to zero to resume ftrace. Acked-by: Steven Rostedt (VMware) Signed-off-by: Naveen N. Rao --- Changes since v2: - Move paca->ftrace_disabled out of CONFIG_BOOK3S_64. - Disable tracing when asked for, not the other way around. arch/powerpc/include/asm/paca.h | 1 + arch/powerpc/kernel/asm-offsets.c | 1 + arch/powerpc/kernel/trace/ftrace_64_mprofile.S | 14 ++++++++++++++ arch/powerpc/kernel/trace/ftrace_64_pg.S | 4 ++++ 4 files changed, 20 insertions(+) diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h index d2bf71dddbef..5be57c20c8c5 100644 --- a/arch/powerpc/include/asm/paca.h +++ b/arch/powerpc/include/asm/paca.h @@ -164,6 +164,7 @@ struct paca_struct { u8 io_sync; /* writel() needs spin_unlock sync */ u8 irq_work_pending; /* IRQ_WORK interrupt while soft-disable */ u8 nap_state_lost; /* NV GPR values lost in power7_idle */ + u8 ftrace_disabled; /* Hard disable ftrace */ u64 sprg_vdso; /* Saved user-visible sprg */ #ifdef CONFIG_PPC_TRANSACTIONAL_MEM u64 tm_scratch; /* TM scratch area for reclaim */ diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c index ea5eb91b836e..775c847f0e33 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_DISABLED, paca_struct, ftrace_disabled); #ifdef CONFIG_PPC_BOOK3S OFFSET(PACACONTEXTID, paca_struct, mm_ctx_id); #ifdef CONFIG_PPC_MM_SLICES diff --git a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S index 3f3e81852422..9d234835e1e6 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_DISABLED(r13) + cmpdi r3, 0 + bne 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..3d8186832a34 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_DISABLED(r13) + cmpdi r3, 0 + bnelr + /* Taken from output of objdump from lib64/glibc */ mflr r3 ld r11, 0(r1) -- 2.16.2