[PATCH v2 0/5] powerpc/ftrace: Add support for ftrace_modify_call() and a few other fixes

[PATCH v2 0/5] powerpc/ftrace: Add support for ftrace_modify_call() and a few other fixes

[Naveen N. Rao]

The first two patches fix a kernel oops when function tracing is enabled 
while using KVM and are v2 of the patches posted at:
https://www.mail-archive.com/linuxppc-dev@lists.ozlabs.org/msg130548.html

Patch 3 is a new patch that tightens how we detect _mcount() call sites 
for -mprofile-kernel during module loading.

The last two patches implement support for ftrace_caller() to 
conditionally save the register state. The existing ftrace_caller() is 
renamed to ftrace_regs_caller() since we save the entire pt_regs today.  
A new implementation of ftrace_caller() that saves the minimum register 
state is provided. We switch between the two variants through 
ftrace_modify_call(). The necessary support to call into the two 
different variants from modules is also added.


- Naveen


Naveen N. Rao (5):
  powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code
    paths
  powerpc64/ftrace: Disable ftrace during kvm guest entry/exit
  powerpc64/module: Tighten detection of mcount call sites with
    -mprofile-kernel
  powerpc64/ftrace: Use the generic version of ftrace_replace_code()
  powerpc64/ftrace: Implement support for ftrace_regs_caller()

 arch/powerpc/include/asm/ftrace.h              |   2 -
 arch/powerpc/include/asm/module.h              |   3 +
 arch/powerpc/include/asm/paca.h                |   1 +
 arch/powerpc/kernel/asm-offsets.c              |   1 +
 arch/powerpc/kernel/module_64.c                |  43 +++--
 arch/powerpc/kernel/trace/ftrace.c             | 210 ++++++++++++++++++++-----
 arch/powerpc/kernel/trace/ftrace_64_mprofile.S |  85 +++++++++-
 arch/powerpc/kernel/trace/ftrace_64_pg.S       |   4 +
 arch/powerpc/kvm/book3s_hv_rmhandlers.S        |   8 +
 9 files changed, 294 insertions(+), 63 deletions(-)

-- 
2.16.2

[PATCH v2 1/5] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths

[Naveen N. Rao]

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.rao@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

Re: [PATCH v2 1/5] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths

[Steven Rostedt]

On Wed, 21 Mar 2018 16:13:18 +0530
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> 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.
> 
> 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.

Looks fine to me:

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

-- Steve

> 
> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
> ---

[PATCH v2 2/5] powerpc64/ftrace: Disable ftrace during kvm guest entry/exit

[Naveen N. Rao]

During guest entry/exit, we switch over to/from the guest MMU context.
While doing so, we set our state to KVM_GUEST_MODE_HOST_HV to note down
the fact that we cannot take any exceptions in the hypervisor code.

Since ftrace may be enabled and since it can result in us taking a trap,
disable ftrace by setting paca->ftrace_disabled. Once we exit the guest
and restore host MMU context, we re-enable ftrace.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
---
 arch/powerpc/kvm/book3s_hv_rmhandlers.S | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index f31f357b8c5a..9292087adb68 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -600,6 +600,10 @@ kvmppc_hv_entry:
 	/* Save R1 in the PACA */
 	std	r1, HSTATE_HOST_R1(r13)
 
+	/* Disable ftrace since we can't take a trap any more */
+	li	r6, 1
+	stb	r6, PACA_FTRACE_DISABLED(r13)
+
 	li	r6, KVM_GUEST_MODE_HOST_HV
 	stb	r6, HSTATE_IN_GUEST(r13)
 
@@ -2048,6 +2052,8 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_TYPE_RADIX)
 	/* Unset guest mode */
 	li	r0, KVM_GUEST_MODE_NONE
 	stb	r0, HSTATE_IN_GUEST(r13)
+	li	r0, 0
+	stb	r0, PACA_FTRACE_DISABLED(r13)
 
 	ld	r0, SFS+PPC_LR_STKOFF(r1)
 	addi	r1, r1, SFS
@@ -3379,6 +3385,8 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_TYPE_RADIX)
 	ld	r8, KVM_HOST_LPCR(r10)
 	mtspr	SPRN_LPCR, r8
 	isync
+	li	r0, 0
+	stb	r0, PACA_FTRACE_DISABLED(r13)
 	li	r0, KVM_GUEST_MODE_NONE
 	stb	r0, HSTATE_IN_GUEST(r13)
 
-- 
2.16.2

[PATCH v2 3/5] powerpc64/module: Tighten detection of mcount call sites with -mprofile-kernel

[Naveen N. Rao]

For R_PPC64_REL24 relocations, we suppress emitting instructions for TOC
load/restore in the relocation stub if the relocation is for _mcount()
call when using -mprofile-kernel ABI.

To detect this, we check if the preceding instructions are per the
standard set of instructions emitted by gcc: either the two instruction
sequence of 'mflr r0; std r0,16(r1)', or the more optimized variant of a
single 'mflr r0'. This is not sufficient since nothing prevents users
from hand coding sequences involving a 'mflr r0' followed by a 'bl'.

For removing the toc save instruction from the stub, we additionally
check if the symbol is "_mcount". Add the same check here as well.

Also rename is_early_mcount_callsite() to is_mprofile_mcount_callsite()
since that is what is being checked. The use of "early" is misleading
since there is nothing involving this function that qualifies as early.

Fixes: 153086644fd1f ("powerpc/ftrace: Add support for -mprofile-kernel ftrace ABI")
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
---
 arch/powerpc/kernel/module_64.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index a2636c250b7b..8413be31d6a4 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -463,8 +463,11 @@ static unsigned long stub_for_addr(const Elf64_Shdr *sechdrs,
 }
 
 #ifdef CC_USING_MPROFILE_KERNEL
-static bool is_early_mcount_callsite(u32 *instruction)
+static bool is_mprofile_mcount_callsite(const char *name, u32 *instruction)
 {
+	if (strcmp("_mcount", name))
+		return false;
+
 	/*
 	 * Check if this is one of the -mprofile-kernel sequences.
 	 */
@@ -496,8 +499,7 @@ static void squash_toc_save_inst(const char *name, unsigned long addr)
 #else
 static void squash_toc_save_inst(const char *name, unsigned long addr) { }
 
-/* without -mprofile-kernel, mcount calls are never early */
-static bool is_early_mcount_callsite(u32 *instruction)
+static bool is_mprofile_mcount_callsite(const char *name, u32 *instruction)
 {
 	return false;
 }
@@ -505,11 +507,11 @@ static bool is_early_mcount_callsite(u32 *instruction)
 
 /* We expect a noop next: if it is, replace it with instruction to
    restore r2. */
-static int restore_r2(u32 *instruction, struct module *me)
+static int restore_r2(const char *name, u32 *instruction, struct module *me)
 {
 	u32 *prev_insn = instruction - 1;
 
-	if (is_early_mcount_callsite(prev_insn))
+	if (is_mprofile_mcount_callsite(name, prev_insn))
 		return 1;
 
 	/*
@@ -650,7 +652,8 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
 				value = stub_for_addr(sechdrs, value, me);
 				if (!value)
 					return -ENOENT;
-				if (!restore_r2((u32 *)location + 1, me))
+				if (!restore_r2(strtab + sym->st_name,
+							(u32 *)location + 1, me))
 					return -ENOEXEC;
 
 				squash_toc_save_inst(strtab + sym->st_name, value);
-- 
2.16.2

[PATCH v2 4/5] powerpc64/ftrace: Use the generic version of ftrace_replace_code()

[Naveen N. Rao]

Our implementation matches that of the generic version, which also
handles FTRACE_UPDATE_MODIFY_CALL. So, remove our implementation in
favor of the generic version.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
---
 arch/powerpc/kernel/trace/ftrace.c | 36 ------------------------------------
 1 file changed, 36 deletions(-)

diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
index 4741fe112f05..80667128db3d 100644
--- a/arch/powerpc/kernel/trace/ftrace.c
+++ b/arch/powerpc/kernel/trace/ftrace.c
@@ -485,42 +485,6 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
 	return ret;
 }
 
-static int __ftrace_replace_code(struct dyn_ftrace *rec, int enable)
-{
-	unsigned long ftrace_addr = (unsigned long)FTRACE_ADDR;
-	int ret;
-
-	ret = ftrace_update_record(rec, enable);
-
-	switch (ret) {
-	case FTRACE_UPDATE_IGNORE:
-		return 0;
-	case FTRACE_UPDATE_MAKE_CALL:
-		return ftrace_make_call(rec, ftrace_addr);
-	case FTRACE_UPDATE_MAKE_NOP:
-		return ftrace_make_nop(NULL, rec, ftrace_addr);
-	}
-
-	return 0;
-}
-
-void ftrace_replace_code(int enable)
-{
-	struct ftrace_rec_iter *iter;
-	struct dyn_ftrace *rec;
-	int ret;
-
-	for (iter = ftrace_rec_iter_start(); iter;
-	     iter = ftrace_rec_iter_next(iter)) {
-		rec = ftrace_rec_iter_record(iter);
-		ret = __ftrace_replace_code(rec, enable);
-		if (ret) {
-			ftrace_bug(ret, rec);
-			return;
-		}
-	}
-}
-
 /*
  * Use the default ftrace_modify_all_code, but without
  * stop_machine().
-- 
2.16.2

[PATCH v2 5/5] powerpc64/ftrace: Implement support for ftrace_regs_caller()

[Naveen N. Rao]

With -mprofile-kernel, we always save the full register state in
ftrace_caller(). While this works, this is inefficient if we're not
interested in the register state, such as when we're using the function
tracer.

Rename the existing ftrace_caller() as ftrace_regs_caller() and provide
a simpler implementation for ftrace_caller() that is used when registers
are not required to be saved.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/ftrace.h              |   2 -
 arch/powerpc/include/asm/module.h              |   3 +
 arch/powerpc/kernel/module_64.c                |  28 +++-
 arch/powerpc/kernel/trace/ftrace.c             | 184 +++++++++++++++++++++++--
 arch/powerpc/kernel/trace/ftrace_64_mprofile.S |  71 +++++++++-
 5 files changed, 262 insertions(+), 26 deletions(-)

diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h
index 9abddde372ab..f7a23c2dce74 100644
--- a/arch/powerpc/include/asm/ftrace.h
+++ b/arch/powerpc/include/asm/ftrace.h
@@ -49,8 +49,6 @@
 extern void _mcount(void);
 
 #ifdef CONFIG_DYNAMIC_FTRACE
-# define FTRACE_ADDR ((unsigned long)ftrace_caller)
-# define FTRACE_REGS_ADDR FTRACE_ADDR
 static inline unsigned long ftrace_call_adjust(unsigned long addr)
 {
        /* reloction of mcount call site is the same as the address */
diff --git a/arch/powerpc/include/asm/module.h b/arch/powerpc/include/asm/module.h
index 7e28442827f1..2d16b6d9147d 100644
--- a/arch/powerpc/include/asm/module.h
+++ b/arch/powerpc/include/asm/module.h
@@ -43,6 +43,9 @@ struct mod_arch_specific {
 #ifdef CONFIG_DYNAMIC_FTRACE
 	unsigned long toc;
 	unsigned long tramp;
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+	unsigned long tramp_regs;
+#endif
 #endif
 
 	/* For module function descriptor dereference */
diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index 8413be31d6a4..f7667e2ebfcb 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -280,6 +280,10 @@ static unsigned long get_stubs_size(const Elf64_Ehdr *hdr,
 #ifdef CONFIG_DYNAMIC_FTRACE
 	/* make the trampoline to the ftrace_caller */
 	relocs++;
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+	/* an additional one for ftrace_regs_caller */
+	relocs++;
+#endif
 #endif
 
 	pr_debug("Looks like a total of %lu stubs, max\n", relocs);
@@ -765,7 +769,8 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
  * via the paca (in r13). The target (ftrace_caller()) is responsible for
  * saving and restoring the toc before returning.
  */
-static unsigned long create_ftrace_stub(const Elf64_Shdr *sechdrs, struct module *me)
+static unsigned long create_ftrace_stub(const Elf64_Shdr *sechdrs,
+				struct module *me, unsigned long addr)
 {
 	struct ppc64_stub_entry *entry;
 	unsigned int i, num_stubs;
@@ -792,9 +797,10 @@ static unsigned long create_ftrace_stub(const Elf64_Shdr *sechdrs, struct module
 	memcpy(entry->jump, stub_insns, sizeof(stub_insns));
 
 	/* Stub uses address relative to kernel toc (from the paca) */
-	reladdr = (unsigned long)ftrace_caller - kernel_toc_addr();
+	reladdr = addr - kernel_toc_addr();
 	if (reladdr > 0x7FFFFFFF || reladdr < -(0x80000000L)) {
-		pr_err("%s: Address of ftrace_caller out of range of kernel_toc.\n", me->name);
+		pr_err("%s: Address of %ps out of range of kernel_toc.\n",
+							me->name, (void *)addr);
 		return 0;
 	}
 
@@ -802,22 +808,30 @@ static unsigned long create_ftrace_stub(const Elf64_Shdr *sechdrs, struct module
 	entry->jump[2] |= PPC_LO(reladdr);
 
 	/* Eventhough we don't use funcdata in the stub, it's needed elsewhere. */
-	entry->funcdata = func_desc((unsigned long)ftrace_caller);
+	entry->funcdata = func_desc(addr);
 	entry->magic = STUB_MAGIC;
 
 	return (unsigned long)entry;
 }
 #else
-static unsigned long create_ftrace_stub(const Elf64_Shdr *sechdrs, struct module *me)
+static unsigned long create_ftrace_stub(const Elf64_Shdr *sechdrs,
+				struct module *me, unsigned long addr)
 {
-	return stub_for_addr(sechdrs, (unsigned long)ftrace_caller, me);
+	return stub_for_addr(sechdrs, addr, me);
 }
 #endif
 
 int module_finalize_ftrace(struct module *mod, const Elf_Shdr *sechdrs)
 {
 	mod->arch.toc = my_r2(sechdrs, mod);
-	mod->arch.tramp = create_ftrace_stub(sechdrs, mod);
+	mod->arch.tramp = create_ftrace_stub(sechdrs, mod,
+					(unsigned long)ftrace_caller);
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+	mod->arch.tramp_regs = create_ftrace_stub(sechdrs, mod,
+					(unsigned long)ftrace_regs_caller);
+	if (!mod->arch.tramp_regs)
+		return -ENOENT;
+#endif
 
 	if (!mod->arch.tramp)
 		return -ENOENT;
diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
index 80667128db3d..79d2924e75d5 100644
--- a/arch/powerpc/kernel/trace/ftrace.c
+++ b/arch/powerpc/kernel/trace/ftrace.c
@@ -357,6 +357,8 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 {
 	unsigned int op[2];
 	void *ip = (void *)rec->ip;
+	unsigned long entry, ptr, tramp;
+	struct module *mod = rec->arch.mod;
 
 	/* read where this goes */
 	if (probe_kernel_read(op, ip, sizeof(op)))
@@ -368,19 +370,44 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 		return -EINVAL;
 	}
 
-	/* If we never set up a trampoline to ftrace_caller, then bail */
-	if (!rec->arch.mod->arch.tramp) {
+	/* If we never set up ftrace trampoline(s), then bail */
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+	if (!mod->arch.tramp || !mod->arch.tramp_regs) {
+#else
+	if (!mod->arch.tramp) {
+#endif
 		pr_err("No ftrace trampoline\n");
 		return -EINVAL;
 	}
 
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+	if (rec->flags & FTRACE_FL_REGS)
+		tramp = mod->arch.tramp_regs;
+	else
+#endif
+		tramp = mod->arch.tramp;
+
+	if (module_trampoline_target(mod, tramp, &ptr)) {
+		pr_err("Failed to get trampoline target\n");
+		return -EFAULT;
+	}
+
+	pr_devel("trampoline target %lx", ptr);
+
+	entry = ppc_global_function_entry((void *)addr);
+	/* This should match what was called */
+	if (ptr != entry) {
+		pr_err("addr %lx does not match expected %lx\n", ptr, entry);
+		return -EINVAL;
+	}
+
 	/* Ensure branch is within 24 bits */
-	if (!create_branch(ip, rec->arch.mod->arch.tramp, BRANCH_SET_LINK)) {
+	if (!create_branch(ip, tramp, BRANCH_SET_LINK)) {
 		pr_err("Branch out of range\n");
 		return -EINVAL;
 	}
 
-	if (patch_branch(ip, rec->arch.mod->arch.tramp, BRANCH_SET_LINK)) {
+	if (patch_branch(ip, tramp, BRANCH_SET_LINK)) {
 		pr_err("REL24 out of range!\n");
 		return -EINVAL;
 	}
@@ -388,14 +415,6 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 	return 0;
 }
 
-#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
-int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
-			unsigned long addr)
-{
-	return ftrace_make_call(rec, addr);
-}
-#endif
-
 #else  /* !CONFIG_PPC64: */
 static int
 __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
@@ -472,6 +491,137 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 #endif /* CONFIG_MODULES */
 }
 
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+#ifdef CONFIG_MODULES
+static int
+__ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
+					unsigned long addr)
+{
+	unsigned int op;
+	unsigned long ip = rec->ip;
+	unsigned long entry, ptr, tramp;
+	struct module *mod = rec->arch.mod;
+
+	/* If we never set up ftrace trampolines, then bail */
+	if (!mod->arch.tramp || !mod->arch.tramp_regs) {
+		pr_err("No ftrace trampoline\n");
+		return -EINVAL;
+	}
+
+	/* read where this goes */
+	if (probe_kernel_read(&op, (void *)ip, sizeof(int))) {
+		pr_err("Fetching opcode failed.\n");
+		return -EFAULT;
+	}
+
+	/* Make sure that that this is still a 24bit jump */
+	if (!is_bl_op(op)) {
+		pr_err("Not expected bl: opcode is %x\n", op);
+		return -EINVAL;
+	}
+
+	/* lets find where the pointer goes */
+	tramp = find_bl_target(ip, op);
+	entry = ppc_global_function_entry((void *)old_addr);
+
+	pr_devel("ip:%lx jumps to %lx", ip, tramp);
+
+	if (tramp != entry) {
+		/* old_addr is not within range, so we must have used a trampoline */
+		if (module_trampoline_target(mod, tramp, &ptr)) {
+			pr_err("Failed to get trampoline target\n");
+			return -EFAULT;
+		}
+
+		pr_devel("trampoline target %lx", ptr);
+
+		/* This should match what was called */
+		if (ptr != entry) {
+			pr_err("addr %lx does not match expected %lx\n", ptr, entry);
+			return -EINVAL;
+		}
+	}
+
+	/* The new target may be within range */
+	if (test_24bit_addr(ip, addr)) {
+		/* within range */
+		if (patch_branch((unsigned int *)ip, addr, BRANCH_SET_LINK)) {
+			pr_err("REL24 out of range!\n");
+			return -EINVAL;
+		}
+
+		return 0;
+	}
+
+	if (rec->flags & FTRACE_FL_REGS)
+		tramp = mod->arch.tramp_regs;
+	else
+		tramp = mod->arch.tramp;
+
+	if (module_trampoline_target(mod, tramp, &ptr)) {
+		pr_err("Failed to get trampoline target\n");
+		return -EFAULT;
+	}
+
+	pr_devel("trampoline target %lx", ptr);
+
+	entry = ppc_global_function_entry((void *)addr);
+	/* This should match what was called */
+	if (ptr != entry) {
+		pr_err("addr %lx does not match expected %lx\n", ptr, entry);
+		return -EINVAL;
+	}
+
+	/* Ensure branch is within 24 bits */
+	if (!create_branch((unsigned int *)ip, tramp, BRANCH_SET_LINK)) {
+		pr_err("Branch out of range\n");
+		return -EINVAL;
+	}
+
+	if (patch_branch((unsigned int *)ip, tramp, BRANCH_SET_LINK)) {
+		pr_err("REL24 out of range!\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+#endif
+
+int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
+			unsigned long addr)
+{
+	unsigned long ip = rec->ip;
+	unsigned int old, new;
+
+	/*
+	 * If the calling address is more that 24 bits away,
+	 * then we had to use a trampoline to make the call.
+	 * Otherwise just update the call site.
+	 */
+	if (test_24bit_addr(ip, addr) && test_24bit_addr(ip, old_addr)) {
+		/* within range */
+		old = ftrace_call_replace(ip, old_addr, 1);
+		new = ftrace_call_replace(ip, addr, 1);
+		return ftrace_modify_code(ip, old, new);
+	}
+
+#ifdef CONFIG_MODULES
+	/*
+	 * Out of range jumps are called from modules.
+	 */
+	if (!rec->arch.mod) {
+		pr_err("No module loaded\n");
+		return -EINVAL;
+	}
+
+	return __ftrace_modify_call(rec, old_addr, addr);
+#else
+	/* We should not get here without modules */
+	return -EINVAL;
+#endif /* CONFIG_MODULES */
+}
+#endif
+
 int ftrace_update_ftrace_func(ftrace_func_t func)
 {
 	unsigned long ip = (unsigned long)(&ftrace_call);
@@ -482,6 +632,16 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
 	new = ftrace_call_replace(ip, (unsigned long)func, 1);
 	ret = ftrace_modify_code(ip, old, new);
 
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+	/* Also update the regs callback function */
+	if (!ret) {
+		ip = (unsigned long)(&ftrace_regs_call);
+		old = *(unsigned int *)&ftrace_regs_call;
+		new = ftrace_call_replace(ip, (unsigned long)func, 1);
+		ret = ftrace_modify_code(ip, old, new);
+	}
+#endif
+
 	return ret;
 }
 
diff --git a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
index 8f2380304ef1..7b81db85f76e 100644
--- a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
+++ b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
@@ -20,8 +20,8 @@
 #ifdef CONFIG_DYNAMIC_FTRACE
 /*
  *
- * ftrace_caller() is the function that replaces _mcount() when ftrace is
- * active.
+ * ftrace_caller()/ftrace_regs_caller() is the function that replaces _mcount()
+ * when ftrace is active.
  *
  * We arrive here after a function A calls function B, and we are the trace
  * function for B. When we enter r1 points to A's stack frame, B has not yet
@@ -37,7 +37,7 @@
  * Our job is to save the register state into a struct pt_regs (on the stack)
  * and then arrange for the ftrace function to be called.
  */
-_GLOBAL(ftrace_caller)
+_GLOBAL(ftrace_regs_caller)
 	/* Save the original return address in A's stack frame */
 	std	r0,LRSAVE(r1)
 
@@ -100,8 +100,8 @@ _GLOBAL(ftrace_caller)
 	addi    r6, r1 ,STACK_FRAME_OVERHEAD
 
 	/* ftrace_call(r3, r4, r5, r6) */
-.globl ftrace_call
-ftrace_call:
+.globl ftrace_regs_call
+ftrace_regs_call:
 	bl	ftrace_stub
 	nop
 
@@ -162,6 +162,7 @@ ftrace_call:
 	bne-	livepatch_handler
 #endif
 
+ftrace_caller_common:
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 .globl ftrace_graph_call
 ftrace_graph_call:
@@ -182,6 +183,66 @@ ftrace_no_trace:
 	mtlr	r0
 	bctr
 
+_GLOBAL(ftrace_caller)
+	/* Save the original return address in A's stack frame */
+	std	r0, LRSAVE(r1)
+
+	/* Create our stack frame + pt_regs */
+	stdu	r1, -SWITCH_FRAME_SIZE(r1)
+
+	/* Save all gprs to pt_regs */
+	SAVE_8GPRS(3, r1)
+
+	lbz	r3, PACA_FTRACE_DISABLED(r13)
+	cmpdi	r3, 0
+	beq	ftrace_no_trace
+
+	/* Get the _mcount() call site out of LR */
+	mflr	r7
+	std     r7, _NIP(r1)
+
+	/* Save callee's TOC in the ABI compliant location */
+	std	r2, 24(r1)
+	ld	r2, PACATOC(r13)	/* get kernel TOC in r2 */
+
+	addis	r3, r2, function_trace_op@toc@ha
+	addi	r3, r3, function_trace_op@toc@l
+	ld	r5, 0(r3)
+
+	/* Calculate ip from nip-4 into r3 for call below */
+	subi    r3, r7, MCOUNT_INSN_SIZE
+
+	/* Put the original return address in r4 as parent_ip */
+	mr	r4, r0
+
+	/* Set pt_regs to NULL */
+	li	r6, 0
+
+	/* ftrace_call(r3, r4, r5, r6) */
+.globl ftrace_call
+ftrace_call:
+	bl	ftrace_stub
+	nop
+
+	ld	r3, _NIP(r1)
+	mtctr	r3
+
+	/* Restore gprs */
+	REST_8GPRS(3,r1)
+
+	/* Restore callee's TOC */
+	ld	r2, 24(r1)
+
+	/* Pop our stack frame */
+	addi	r1, r1, SWITCH_FRAME_SIZE
+
+	/* Reload original LR */
+	ld	r0, LRSAVE(r1)
+	mtlr	r0
+
+	/* Handle function_graph or go back */
+	b	ftrace_caller_common
+
 #ifdef CONFIG_LIVEPATCH
 	/*
 	 * This function runs in the mcount context, between two functions. As
-- 
2.16.2

Re: [PATCH v2 5/5] powerpc64/ftrace: Implement support for ftrace_regs_caller()

[Steven Rostedt]

On Wed, 21 Mar 2018 16:13:22 +0530
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:

>  int module_finalize_ftrace(struct module *mod, const Elf_Shdr *sechdrs)
>  {
>  	mod->arch.toc = my_r2(sechdrs, mod);
> -	mod->arch.tramp = create_ftrace_stub(sechdrs, mod);
> +	mod->arch.tramp = create_ftrace_stub(sechdrs, mod,
> +					(unsigned long)ftrace_caller);
> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> +	mod->arch.tramp_regs = create_ftrace_stub(sechdrs, mod,
> +					(unsigned long)ftrace_regs_caller);

So you only reference ftrace_regs_caller if you have
DYNAMIC_FTRACE_WITH_REGS defined?

> +	if (!mod->arch.tramp_regs)
> +		return -ENOENT;
> +#endif
>  
>  	if (!mod->arch.tramp)
>  		return -ENOENT;


> diff --git a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
> index 8f2380304ef1..7b81db85f76e 100644
> --- a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
> +++ b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
> @@ -20,8 +20,8 @@
>  #ifdef CONFIG_DYNAMIC_FTRACE
>  /*
>   *
> - * ftrace_caller() is the function that replaces _mcount() when ftrace is
> - * active.
> + * ftrace_caller()/ftrace_regs_caller() is the function that replaces _mcount()
> + * when ftrace is active.
>   *
>   * We arrive here after a function A calls function B, and we are the trace
>   * function for B. When we enter r1 points to A's stack frame, B has not yet
> @@ -37,7 +37,7 @@
>   * Our job is to save the register state into a struct pt_regs (on the stack)
>   * and then arrange for the ftrace function to be called.
>   */

Perhaps you want to add:

#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS

here.

> -_GLOBAL(ftrace_caller)
> +_GLOBAL(ftrace_regs_caller)
>  	/* Save the original return address in A's stack frame */
>  	std	r0,LRSAVE(r1)
>  
> @@ -100,8 +100,8 @@ _GLOBAL(ftrace_caller)
>  	addi    r6, r1 ,STACK_FRAME_OVERHEAD
>  
>  	/* ftrace_call(r3, r4, r5, r6) */
> -.globl ftrace_call
> -ftrace_call:
> +.globl ftrace_regs_call
> +ftrace_regs_call:
>  	bl	ftrace_stub
>  	nop
>  
> @@ -162,6 +162,7 @@ ftrace_call:
>  	bne-	livepatch_handler
>  #endif
>  
> +ftrace_caller_common:
>  #ifdef CONFIG_FUNCTION_GRAPH_TRACER
>  .globl ftrace_graph_call
>  ftrace_graph_call:
> @@ -182,6 +183,66 @@ ftrace_no_trace:
>  	mtlr	r0
>  	bctr
>  
> +_GLOBAL(ftrace_caller)
> +	/* Save the original return address in A's stack frame */
> +	std	r0, LRSAVE(r1)
> +
> +	/* Create our stack frame + pt_regs */
> +	stdu	r1, -SWITCH_FRAME_SIZE(r1)
> +
> +	/* Save all gprs to pt_regs */
> +	SAVE_8GPRS(3, r1)
> +
> +	lbz	r3, PACA_FTRACE_DISABLED(r13)
> +	cmpdi	r3, 0
> +	beq	ftrace_no_trace

Of course you would need to keep the ftrace_no_trace part out of the
#if block then.

-- Steve

> +
> +	/* Get the _mcount() call site out of LR */
> +	mflr	r7
> +	std     r7, _NIP(r1)
> +
> +	/* Save callee's TOC in the ABI compliant location */
> +	std	r2, 24(r1)
> +	ld	r2, PACATOC(r13)	/* get kernel TOC in r2 */
> +
> +	addis	r3, r2, function_trace_op@toc@ha
> +	addi	r3, r3, function_trace_op@toc@l
> +	ld	r5, 0(r3)
> +
> +	/* Calculate ip from nip-4 into r3 for call below */
> +	subi    r3, r7, MCOUNT_INSN_SIZE
> +
> +	/* Put the original return address in r4 as parent_ip */
> +	mr	r4, r0
> +
> +	/* Set pt_regs to NULL */
> +	li	r6, 0
> +
> +	/* ftrace_call(r3, r4, r5, r6) */
> +.globl ftrace_call
> +ftrace_call:
> +	bl	ftrace_stub
> +	nop
> +
> +	ld	r3, _NIP(r1)
> +	mtctr	r3
> +
> +	/* Restore gprs */
> +	REST_8GPRS(3,r1)
> +
> +	/* Restore callee's TOC */
> +	ld	r2, 24(r1)
> +
> +	/* Pop our stack frame */
> +	addi	r1, r1, SWITCH_FRAME_SIZE
> +
> +	/* Reload original LR */
> +	ld	r0, LRSAVE(r1)
> +	mtlr	r0
> +
> +	/* Handle function_graph or go back */
> +	b	ftrace_caller_common
> +
>  #ifdef CONFIG_LIVEPATCH
>  	/*
>  	 * This function runs in the mcount context, between two functions. As

Re: [PATCH v2 5/5] powerpc64/ftrace: Implement support for ftrace_regs_caller()

[Naveen N. Rao]

Steven Rostedt wrote:
> On Wed, 21 Mar 2018 16:13:22 +0530
> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:
>=20
>>  int module_finalize_ftrace(struct module *mod, const Elf_Shdr *sechdrs)
>>  {
>>  	mod->arch.toc =3D my_r2(sechdrs, mod);
>> -	mod->arch.tramp =3D create_ftrace_stub(sechdrs, mod);
>> +	mod->arch.tramp =3D create_ftrace_stub(sechdrs, mod,
>> +					(unsigned long)ftrace_caller);
>> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
>> +	mod->arch.tramp_regs =3D create_ftrace_stub(sechdrs, mod,
>> +					(unsigned long)ftrace_regs_caller);
>=20
> So you only reference ftrace_regs_caller if you have
> DYNAMIC_FTRACE_WITH_REGS defined?

Yes.

>=20
>> +	if (!mod->arch.tramp_regs)
>> +		return -ENOENT;
>> +#endif
>> =20
>>  	if (!mod->arch.tramp)
>>  		return -ENOENT;
>=20
>=20
>> diff --git a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S b/arch/power=
pc/kernel/trace/ftrace_64_mprofile.S
>> index 8f2380304ef1..7b81db85f76e 100644
>> --- a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
>> +++ b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
>> @@ -20,8 +20,8 @@
>>  #ifdef CONFIG_DYNAMIC_FTRACE
>>  /*
>>   *
>> - * ftrace_caller() is the function that replaces _mcount() when ftrace =
is
>> - * active.
>> + * ftrace_caller()/ftrace_regs_caller() is the function that replaces _=
mcount()
>> + * when ftrace is active.
>>   *
>>   * We arrive here after a function A calls function B, and we are the t=
race
>>   * function for B. When we enter r1 points to A's stack frame, B has no=
t yet
>> @@ -37,7 +37,7 @@
>>   * Our job is to save the register state into a struct pt_regs (on the =
stack)
>>   * and then arrange for the ftrace function to be called.
>>   */
>=20
> Perhaps you want to add:
>=20
> #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
>=20
> here.

I think that will always be set here. ftrace_64_mprofile.S is only built=20
for -mprofile-kernel and we select HAVE_DYNAMIC_FTRACE_WITH_REGS if=20
MPROFILE_KERNEL is enabled. It looks like there is no way to unset just=20
CONFIG_DYNAMIC_FTRACE_WITH_REGS and so, for -mprofile-kernel, we can=20
assume it is always set?

- Naveen

=

Re: [PATCH v2 5/5] powerpc64/ftrace: Implement support for ftrace_regs_caller()

[Steven Rostedt]

On Wed, 21 Mar 2018 20:07:32 +0530
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:

> I think that will always be set here. ftrace_64_mprofile.S is only built 
> for -mprofile-kernel and we select HAVE_DYNAMIC_FTRACE_WITH_REGS if 
> MPROFILE_KERNEL is enabled. It looks like there is no way to unset just 
> CONFIG_DYNAMIC_FTRACE_WITH_REGS and so, for -mprofile-kernel, we can 
> assume it is always set?

OK, if that's the case, then I'm fine with it.

-- Steve

Re: [PATCH v2 5/5] powerpc64/ftrace: Implement support for ftrace_regs_caller()

[Naveen N. Rao]

Steven Rostedt wrote:
> On Wed, 21 Mar 2018 20:07:32 +0530
> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:
>=20
>> I think that will always be set here. ftrace_64_mprofile.S is only built=
=20
>> for -mprofile-kernel and we select HAVE_DYNAMIC_FTRACE_WITH_REGS if=20
>> MPROFILE_KERNEL is enabled. It looks like there is no way to unset just=20
>> CONFIG_DYNAMIC_FTRACE_WITH_REGS and so, for -mprofile-kernel, we can=20
>> assume it is always set?
>=20
> OK, if that's the case, then I'm fine with it.

Thanks for the review!

- Naveen

=

Re: [PATCH v2 5/5] powerpc64/ftrace: Implement support for ftrace_regs_caller()

[Steven Rostedt]

On Wed, 21 Mar 2018 20:59:03 +0530
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:

> Thanks for the review!

You're welcome. Note, I did put "Acked-by" and not "Reviewed-by"
because my "Reviewed-by" is usually a bit more thorough than what I did
for your patches. That's because it's been a while since I have worked
on PPC and don't feel comfortable adding "Reviewed-by" for PPC code. :-/

-- Steve

Re: [PATCH v2 5/5] powerpc64/ftrace: Implement support for ftrace_regs_caller()

[Naveen N. Rao]

Steven Rostedt wrote:
> On Wed, 21 Mar 2018 20:59:03 +0530
> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:
>=20
>> Thanks for the review!
>=20
> You're welcome. Note, I did put "Acked-by" and not "Reviewed-by"
> because my "Reviewed-by" is usually a bit more thorough than what I did
> for your patches. That's because it's been a while since I have worked
> on PPC and don't feel comfortable adding "Reviewed-by" for PPC code. :-/

Sure, I understand. As long as the rest of the changes look fine, that's=20
good. Michael Ellerman wrote the -mprofile-kernel ftrace_caller()=20
implementation, so I'll look forward to his review of that part.

- Naveen

=

Re: [PATCH v2 1/5] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths

[Naveen N. Rao]

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 <naveen.n.rao@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=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

=