From: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
To: Michael Ellerman <mpe@ellerman.id.au>,
Steven Rostedt <rostedt@goodmis.org>,
Paul Mackerras <paulus@ozlabs.org>
Cc: linuxppc-dev@lists.ozlabs.org, Anton Blanchard <anton@samba.org>,
Nicholas Piggin <npiggin@gmail.com>,
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 [thread overview]
Message-ID: <fa3e12766e7dd9e28ebea36a7eadab1e2782515c.1521713762.git.naveen.n.rao@linux.vnet.ibm.com> (raw)
In-Reply-To: <cover.1521713762.git.naveen.n.rao@linux.vnet.ibm.com>
In-Reply-To: <cover.1521713762.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_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) <rostedt@goodmis.org>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
---
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
next prev parent reply other threads:[~2018-03-22 10:25 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-22 10:25 [PATCH v3 0/6] powerpc64/ftrace: Add support for ftrace_modify_call() and a few other fixes Naveen N. Rao
2018-03-22 10:25 ` Naveen N. Rao [this message]
2018-03-22 10:25 ` [PATCH v3 2/6] powerpc64/ftrace: Disable ftrace during kvm guest entry/exit Naveen N. Rao
2018-03-22 10:25 ` [PATCH v3 3/6] powerpc/kexec: Disable ftrace before switching to the new kernel Naveen N. Rao
2018-03-26 22:30 ` Michael Ellerman
2018-03-26 22:32 ` Michael Ellerman
2018-03-27 6:53 ` Naveen N. Rao
2018-03-22 10:25 ` [PATCH v3 4/6] powerpc64/module: Tighten detection of mcount call sites with -mprofile-kernel Naveen N. Rao
2018-03-22 10:25 ` [PATCH v3 5/6] powerpc64/ftrace: Use the generic version of ftrace_replace_code() Naveen N. Rao
2018-03-22 10:25 ` [PATCH v3 6/6] powerpc64/ftrace: Implement support for ftrace_regs_caller() Naveen N. Rao
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