powerpc/ftrace: Add support for DYNAMIC_FTRACE_WITH_CALL_OPS

JIRA: https://issues.redhat.com/browse/RHEL-24555

commit e717754
Author: Naveen N Rao <naveen@kernel.org>
Date:   Wed Oct 30 12:38:47 2024 +0530

    powerpc/ftrace: Add support for DYNAMIC_FTRACE_WITH_CALL_OPS

    Implement support for DYNAMIC_FTRACE_WITH_CALL_OPS similar to the
    arm64 implementation.

    This works by patching-in a pointer to an associated ftrace_ops
    structure before each traceable function. If multiple ftrace_ops are
    associated with a call site, then a special ftrace_list_ops is used to
    enable iterating over all the registered ftrace_ops. If no ftrace_ops
    are associated with a call site, then a special ftrace_nop_ops structure
    is used to render the ftrace call as a no-op. ftrace trampoline can then
    read the associated ftrace_ops for a call site by loading from an offset
    from the LR, and branch directly to the associated function.

    The primary advantage with this approach is that we don't have to
    iterate over all the registered ftrace_ops for call sites that have a
    single ftrace_ops registered. This is the equivalent of implementing
    support for dynamic ftrace trampolines, which set up a special ftrace
    trampoline for each registered ftrace_ops and have individual call sites
    branch into those directly.

    A secondary advantage is that this gives us a way to add support for
    direct ftrace callers without having to resort to using stubs. The
    address of the direct call trampoline can be loaded from the ftrace_ops
    structure.

    To support this, we reserve a nop before each function on 32-bit
    powerpc. For 64-bit powerpc, two nops are reserved before each
    out-of-line stub. During ftrace activation, we update this location with
    the associated ftrace_ops pointer. Then, on ftrace entry, we load from
    this location and call into ftrace_ops->func().

    For 64-bit powerpc, we ensure that the out-of-line stub area is
    doubleword aligned so that ftrace_ops address can be updated atomically.

    Signed-off-by: Naveen N Rao <naveen@kernel.org>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Link: https://patch.msgid.link/20241030070850.1361304-15-hbathini@linux.ibm.com

Signed-off-by: Viktor Malik <vmalik@redhat.com>

Author: viktormalik

arch/powerpc/Kconfig

@@ -236,6 +236,7 @@ config PPC
 	select HAVE_DEBUG_STACKOVERFLOW
 	select HAVE_DYNAMIC_FTRACE
 	select HAVE_DYNAMIC_FTRACE_WITH_ARGS	if ARCH_USING_PATCHABLE_FUNCTION_ENTRY || MPROFILE_KERNEL || PPC32
+	select HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS if PPC_FTRACE_OUT_OF_LINE || (PPC32 && ARCH_USING_PATCHABLE_FUNCTION_ENTRY)
 	select HAVE_DYNAMIC_FTRACE_WITH_REGS	if ARCH_USING_PATCHABLE_FUNCTION_ENTRY || MPROFILE_KERNEL || PPC32
 	select HAVE_EBPF_JIT
 	select HAVE_EFFICIENT_UNALIGNED_ACCESS

arch/powerpc/Makefile

@@ -158,8 +158,12 @@ KBUILD_CPPFLAGS	+= -DCC_USING_PATCHABLE_FUNCTION_ENTRY
 ifdef CONFIG_PPC_FTRACE_OUT_OF_LINE
 CC_FLAGS_FTRACE := -fpatchable-function-entry=1
 else
+ifdef CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS # PPC32 only
+CC_FLAGS_FTRACE := -fpatchable-function-entry=3,1
+else
 CC_FLAGS_FTRACE := -fpatchable-function-entry=2
 endif
+endif
 else
 CC_FLAGS_FTRACE := -pg
 ifdef CONFIG_MPROFILE_KERNEL

arch/powerpc/include/asm/ftrace.h

@@ -136,8 +136,11 @@ static inline u8 this_cpu_get_ftrace_enabled(void) { return 1; }
 extern unsigned int ftrace_tramp_text[], ftrace_tramp_init[];
 #ifdef CONFIG_PPC_FTRACE_OUT_OF_LINE
 struct ftrace_ool_stub {
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS
+	struct ftrace_ops *ftrace_op;
+#endif
 	u32	insn[4];
-};
+} __aligned(sizeof(unsigned long));
 extern struct ftrace_ool_stub ftrace_ool_stub_text_end[], ftrace_ool_stub_text[],
 			      ftrace_ool_stub_inittext[];
 extern unsigned int ftrace_ool_stub_text_end_count, ftrace_ool_stub_text_count,

arch/powerpc/kernel/asm-offsets.c

@@ -681,5 +681,9 @@ int main(void)
 	DEFINE(FTRACE_OOL_STUB_SIZE, sizeof(struct ftrace_ool_stub));
 #endif
 
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS
+	OFFSET(FTRACE_OPS_FUNC, ftrace_ops, func);
+#endif
+
 	return 0;
 }

arch/powerpc/kernel/trace/ftrace.c

@@ -38,8 +38,11 @@ unsigned long ftrace_call_adjust(unsigned long addr)
 		return 0;
 
 	if (IS_ENABLED(CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY) &&
-	    !IS_ENABLED(CONFIG_PPC_FTRACE_OUT_OF_LINE))
+	    !IS_ENABLED(CONFIG_PPC_FTRACE_OUT_OF_LINE)) {
 		addr += MCOUNT_INSN_SIZE;
+		if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS))
+			addr += MCOUNT_INSN_SIZE;
+	}
 
 	return addr;
 }
@@ -264,6 +267,46 @@ static int ftrace_init_ool_stub(struct module *mod, struct dyn_ftrace *rec)
 #endif
 }
 
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS
+static const struct ftrace_ops *powerpc_rec_get_ops(struct dyn_ftrace *rec)
+{
+	const struct ftrace_ops *ops = NULL;
+
+	if (rec->flags & FTRACE_FL_CALL_OPS_EN) {
+		ops = ftrace_find_unique_ops(rec);
+		WARN_ON_ONCE(!ops);
+	}
+
+	if (!ops)
+		ops = &ftrace_list_ops;
+
+	return ops;
+}
+
+static int ftrace_rec_set_ops(struct dyn_ftrace *rec, const struct ftrace_ops *ops)
+{
+	if (IS_ENABLED(CONFIG_PPC_FTRACE_OUT_OF_LINE))
+		return patch_ulong((void *)(ftrace_get_ool_stub(rec) - sizeof(unsigned long)),
+				   (unsigned long)ops);
+	else
+		return patch_ulong((void *)(rec->ip - MCOUNT_INSN_SIZE - sizeof(unsigned long)),
+				   (unsigned long)ops);
+}
+
+static int ftrace_rec_set_nop_ops(struct dyn_ftrace *rec)
+{
+	return ftrace_rec_set_ops(rec, &ftrace_nop_ops);
+}
+
+static int ftrace_rec_update_ops(struct dyn_ftrace *rec)
+{
+	return ftrace_rec_set_ops(rec, powerpc_rec_get_ops(rec));
+}
+#else
+static int ftrace_rec_set_nop_ops(struct dyn_ftrace *rec) { return 0; }
+static int ftrace_rec_update_ops(struct dyn_ftrace *rec) { return 0; }
+#endif
+
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
 int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr, unsigned long addr)
 {
@@ -294,6 +337,10 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 	if (!ret)
 		ret = ftrace_modify_code(ip, old, new);
 
+	ret = ftrace_rec_update_ops(rec);
+	if (ret)
+		return ret;
+
 	if (!ret && IS_ENABLED(CONFIG_PPC_FTRACE_OUT_OF_LINE))
 		ret = ftrace_modify_code(rec->ip, ppc_inst(PPC_RAW_NOP()),
 			 ppc_inst(PPC_RAW_BRANCH((long)ftrace_get_ool_stub(rec) - (long)rec->ip)));
@@ -345,16 +392,19 @@ void ftrace_replace_code(int enable)
 		case FTRACE_UPDATE_MODIFY_CALL:
 			ret = ftrace_get_call_inst(rec, new_addr, &new_call_inst);
 			ret |= ftrace_get_call_inst(rec, addr, &call_inst);
+			ret |= ftrace_rec_update_ops(rec);
 			old = call_inst;
 			new = new_call_inst;
 			break;
 		case FTRACE_UPDATE_MAKE_NOP:
 			ret = ftrace_get_call_inst(rec, addr, &call_inst);
+			ret |= ftrace_rec_set_nop_ops(rec);
 			old = call_inst;
 			new = nop_inst;
 			break;
 		case FTRACE_UPDATE_MAKE_CALL:
 			ret = ftrace_get_call_inst(rec, new_addr, &call_inst);
+			ret |= ftrace_rec_update_ops(rec);
 			old = nop_inst;
 			new = call_inst;
 			break;
@@ -470,6 +520,13 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
 	ppc_inst_t old, new;
 	int ret;
 
+	/*
+	 * When using CALL_OPS, the function to call is associated with the
+	 * call site, and we don't have a global function pointer to update.
+	 */
+	if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS))
+		return 0;
+
 	old = ppc_inst_read((u32 *)&ftrace_call);
 	new = ftrace_create_branch_inst(ip, ppc_function_entry(func), 1);
 	ret = ftrace_modify_code(ip, old, new);

arch/powerpc/kernel/trace/ftrace_entry.S

@@ -85,11 +85,21 @@
 	/* Save callee's TOC in the ABI compliant location */
 	std	r2, STK_GOT(r1)
 	LOAD_PACA_TOC()		/* get kernel TOC in r2 */
+#endif
+
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS
+	/* r7 points to the instruction following the call to ftrace */
+	PPC_LL	r5, -(MCOUNT_INSN_SIZE*2 + SZL)(r7)
+	PPC_LL	r12, FTRACE_OPS_FUNC(r5)
+	mtctr	r12
+#else /* !CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS */
+#ifdef CONFIG_PPC64
 	LOAD_REG_ADDR(r3, function_trace_op)
 	ld	r5,0(r3)
 #else
 	lis	r3,function_trace_op@ha
 	lwz	r5,function_trace_op@l(r3)
+#endif
 #endif
 
 	/* Save special regs */
@@ -205,20 +215,30 @@
 #endif
 .endm
 
-_GLOBAL(ftrace_regs_caller)
-	ftrace_regs_entry 1
-	/* ftrace_call(r3, r4, r5, r6) */
+.macro ftrace_regs_func allregs
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS
+	bctrl
+#else
+	.if \allregs == 1
 .globl ftrace_regs_call
 ftrace_regs_call:
+	.else
+.globl ftrace_call
+ftrace_call:
+	.endif
+	/* ftrace_call(r3, r4, r5, r6) */
 	bl	ftrace_stub
+#endif
+.endm
+
+_GLOBAL(ftrace_regs_caller)
+	ftrace_regs_entry 1
+	ftrace_regs_func 1
 	ftrace_regs_exit 1
 
 _GLOBAL(ftrace_caller)
 	ftrace_regs_entry 0
-	/* ftrace_call(r3, r4, r5, r6) */
-.globl ftrace_call
-ftrace_call:
-	bl	ftrace_stub
+	ftrace_regs_func 0
 	ftrace_regs_exit 0
 
 _GLOBAL(ftrace_stub)
@@ -377,7 +397,7 @@ _GLOBAL(return_to_handler)
 #ifdef CONFIG_PPC_FTRACE_OUT_OF_LINE
 SYM_DATA(ftrace_ool_stub_text_count, .long CONFIG_PPC_FTRACE_OUT_OF_LINE_NUM_RESERVE)
 
-SYM_CODE_START(ftrace_ool_stub_text)
+SYM_START(ftrace_ool_stub_text, SYM_L_GLOBAL, .balign SZL)
 	.space CONFIG_PPC_FTRACE_OUT_OF_LINE_NUM_RESERVE * FTRACE_OOL_STUB_SIZE
 SYM_CODE_END(ftrace_ool_stub_text)
 #endif

arch/powerpc/tools/ftrace-gen-ool-stubs.sh

@@ -28,12 +28,13 @@ fi
 
 cat > "$arch_vmlinux_S" <<EOF
 #include <asm/asm-offsets.h>
+#include <asm/ppc_asm.h>
 #include <linux/linkage.h>
 
 .pushsection .tramp.ftrace.text,"aw"
 SYM_DATA(ftrace_ool_stub_text_end_count, .long $num_ool_stubs_text_end)
 
-SYM_CODE_START(ftrace_ool_stub_text_end)
+SYM_START(ftrace_ool_stub_text_end, SYM_L_GLOBAL, .balign SZL)
 #if $num_ool_stubs_text_end
 	.space $num_ool_stubs_text_end * FTRACE_OOL_STUB_SIZE
 #endif
@@ -43,7 +44,7 @@ SYM_CODE_END(ftrace_ool_stub_text_end)
 .pushsection .tramp.ftrace.init,"aw"
 SYM_DATA(ftrace_ool_stub_inittext_count, .long $num_ool_stubs_inittext)
 
-SYM_CODE_START(ftrace_ool_stub_inittext)
+SYM_START(ftrace_ool_stub_inittext, SYM_L_GLOBAL, .balign SZL)
 	.space $num_ool_stubs_inittext * FTRACE_OOL_STUB_SIZE
 SYM_CODE_END(ftrace_ool_stub_inittext)
 .popsection