From: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
To: Michael Ellerman <mpe@ellerman.id.au>,
Steven Rostedt <rostedt@goodmis.org>
Cc: linuxppc-dev@lists.ozlabs.org, Paul Mackerras <paulus@ozlabs.org>,
Nicholas Piggin <npiggin@gmail.com>,
Anton Blanchard <anton@samba.org>,
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 [thread overview]
Message-ID: <bff5845923c4bea9fa7ef9dcb31a138afe273302.1522784883.git.naveen.n.rao@linux.vnet.ibm.com> (raw)
In-Reply-To: <cover.1522784883.git.naveen.n.rao@linux.vnet.ibm.com>
In-Reply-To: <cover.1522784883.git.naveen.n.rao@linux.vnet.ibm.com>
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 <naveen.n.rao@linux.vnet.ibm.com>
---
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
next prev parent reply other threads:[~2018-04-03 20:12 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-03 20:12 [PATCH v4 00/10] powerpc64/ftrace: Add support for ftrace_modify_call() and a few other fixes Naveen N. Rao
2018-04-03 20:12 ` Naveen N. Rao [this message]
2018-04-03 20:12 ` [PATCH v4 02/10] powerpc64/ftrace: Disable ftrace during kvm guest entry/exit Naveen N. Rao
2018-04-03 20:12 ` [PATCH v4 03/10] powerpc64/ftrace: Rearrange #ifdef sections in ftrace.h Naveen N. Rao
2018-04-03 20:12 ` [PATCH v4 04/10] powerpc64/ftrace: Add helpers to hard disable ftrace Naveen N. Rao
2018-04-03 20:12 ` [PATCH v4 05/10] powerpc64/ftrace: Delay enabling ftrace on secondary cpus Naveen N. Rao
2018-04-03 20:12 ` [PATCH v4 06/10] powerpc64/ftrace: Disable ftrace during hotplug Naveen N. Rao
2018-04-03 20:12 ` [PATCH v4 07/10] powerpc64/kexec: Hard disable ftrace before switching to the new kernel Naveen N. Rao
2018-04-03 20:12 ` [PATCH v4 08/10] powerpc64/module: Tighten detection of mcount call sites with -mprofile-kernel Naveen N. Rao
2018-04-03 20:12 ` [PATCH v4 09/10] powerpc64/ftrace: Use the generic version of ftrace_replace_code() Naveen N. Rao
2018-04-03 20:12 ` [PATCH v4 10/10] powerpc64/ftrace: Implement support for ftrace_regs_caller() Naveen N. Rao
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