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.
Signed-off-by: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com>
---
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
better cache performance in the normal case when ftrace is enabled.
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..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
/* 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_area);
OFFSET(PACA_EXRFI, paca_struct, exrfi);
OFFSET(PACA_L1D_FLUSH_SIZE, paca_struct, l1d_flush_size);
+ OFFSET(PACA_FTRACE_DISABLED, paca_struct, ftrace_disabled);
#endif
OFFSET(PACAHWCPUID, paca_struct, hw_cpu_id);
diff --git a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
b/arch/powerpc/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
+
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
