From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (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 406JnR2x9QzF1t9 for ; Thu, 22 Mar 2018 18:53:15 +1100 (AEDT) Received: from pps.filterd (m0098416.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w2M7oDHR194280 for ; Thu, 22 Mar 2018 03:53:12 -0400 Received: from e06smtp14.uk.ibm.com (e06smtp14.uk.ibm.com [195.75.94.110]) by mx0b-001b2d01.pphosted.com with ESMTP id 2gv89kgdjq-1 (version=TLSv1.2 cipher=AES256-SHA256 bits=256 verify=NOT) for ; Thu, 22 Mar 2018 03:53:12 -0400 Received: from localhost by e06smtp14.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 22 Mar 2018 07:53:10 -0000 Date: Thu, 22 Mar 2018 13:23:05 +0530 From: "Naveen N. Rao" Subject: Re: [PATCH v2 1/5] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths To: Michael Ellerman , Paul Mackerras , Steven Rostedt Cc: Anton Blanchard , linuxppc-dev@lists.ozlabs.org, Nicholas Piggin , sathnaga@linux.vnet.ibm.com References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Message-Id: <1521705085.6fya98gc1m.naveen@linux.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Naveen N. Rao wrote: > 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. >=20 > 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. >=20 > Signed-off-by: Naveen N. Rao > --- > Changes since v1: > - Do not guard the paca field check within CONFIG_KVM. > - Move the early return code out of the usual path to optimize for=20 > better cache performance in the normal case when ftrace is enabled. >=20 > 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(+) >=20 > diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/p= aca.h > index d2bf71dddbef..4f47adc2a408 100644 > --- a/arch/powerpc/include/asm/paca.h > +++ b/arch/powerpc/include/asm/paca.h > @@ -211,6 +211,7 @@ struct paca_struct { > u16 in_mce; > u8 hmi_event_available; /* HMI event is available */ > u8 hmi_p9_special_emu; /* HMI P9 special emulation */ > + u8 ftrace_disabled; > #endif > =20 > /* Stuff for accurate time accounting */ > diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-= offsets.c > index ea5eb91b836e..8e4fc96ff6bc 100644 > --- a/arch/powerpc/kernel/asm-offsets.c > +++ b/arch/powerpc/kernel/asm-offsets.c > @@ -240,6 +240,7 @@ int main(void) > OFFSET(PACA_RFI_FLUSH_FALLBACK_AREA, paca_struct, rfi_flush_fallback_ar= ea); > OFFSET(PACA_EXRFI, paca_struct, exrfi); > OFFSET(PACA_L1D_FLUSH_SIZE, paca_struct, l1d_flush_size); > + OFFSET(PACA_FTRACE_DISABLED, paca_struct, ftrace_disabled); > =20 > #endif > OFFSET(PACAHWCPUID, paca_struct, hw_cpu_id); > diff --git a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S b/arch/powerp= c/kernel/trace/ftrace_64_mprofile.S > index 3f3e81852422..8f2380304ef1 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 > + beq ftrace_no_trace ^^^ bne :facepalm: - Naveen =