[PATCH v2 1/5] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths
From: Naveen N. Rao <hidden>
Date: 2018-03-21 10:44:37
Subsystem:
function hooks (ftrace), linux for powerpc (32-bit and 64-bit), the rest · Maintainers:
Steven Rostedt, Masami Hiramatsu, Madhavan Srinivasan, Linus Torvalds
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 <redacted> --- 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