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Date: Thu, 14 Apr 2022 05:58:45 +0000 From: Song Liu <songliubraving@...com> To: Xu Kuohai <xukuohai@...wei.com> CC: bpf <bpf@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, open list <linux-kernel@...r.kernel.org>, Networking <netdev@...r.kernel.org>, "open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>, Will Deacon <will@...nel.org>, Steven Rostedt <rostedt@...dmis.org>, Daniel Borkmann <daniel@...earbox.net>, Alexei Starovoitov <ast@...nel.org>, Zi Shen Lim <zlim.lnx@...il.com>, Andrii Nakryiko <andrii@...nel.org>, Martin Lau <kafai@...com>, Yonghong Song <yhs@...com>, John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>, Shuah Khan <shuah@...nel.org>, Mark Rutland <mark.rutland@....com>, Ard Biesheuvel <ardb@...nel.org>, Pasha Tatashin <pasha.tatashin@...een.com>, Peter Collingbourne <pcc@...gle.com>, Daniel Kiss <daniel.kiss@....com>, Sudeep Holla <sudeep.holla@....com>, Steven Price <steven.price@....com>, Marc Zyngier <maz@...nel.org>, Mark Brown <broonie@...nel.org>, Kumar Kartikeya Dwivedi <memxor@...il.com>, Delyan Kratunov <delyank@...com> Subject: Re: [PATCH bpf-next 1/5] arm64: ftrace: Add ftrace direct call support > On Apr 12, 2022, at 10:49 PM, Xu Kuohai <xukuohai@...wei.com> wrote: > > Add ftrace direct support for arm64. > > 1. When there is custom trampoline only, replace the fentry nop to a > jump instruction that jumps directly to the custom trampoline. > > 2. When ftrace trampoline and custome coexist, jump from fentry to > ftrace trampoline first, then jump to custom trampoline when ftrace > trampoline exits. The currently unused register pt_regs->x0 is used > as an intermediary for jumping from ftrace trampoline to custom > trampoline. > > Signed-off-by: Xu Kuohai <xukuohai@...wei.com> For the series: Acked-by: Song Liu <songliubraving@...com> (Pardon my laziness, I somehow only got 1/5 and 3/5 in one of my inboxes, and nothing in my other inbox. :( ) Just one nitpick for 2/5: as we move is_valid_bpf_tramp_flags to trampoline.c, we should change the multi-line comment into net style: /* BPF_TRAMP_F_RET_FENTRY_RET is only used by bpf_struct_ops, * and it must be used alone. */ Thanks, Song > --- > arch/arm64/Kconfig | 2 ++ > arch/arm64/include/asm/ftrace.h | 10 ++++++++++ > arch/arm64/kernel/asm-offsets.c | 1 + > arch/arm64/kernel/entry-ftrace.S | 18 +++++++++++++++--- > 4 files changed, 28 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 57c4c995965f..81cc330daafc 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -177,6 +177,8 @@ config ARM64 > select HAVE_DYNAMIC_FTRACE > select HAVE_DYNAMIC_FTRACE_WITH_REGS \ > if $(cc-option,-fpatchable-function-entry=2) > + select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS \ > + if DYNAMIC_FTRACE_WITH_REGS > select FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY \ > if DYNAMIC_FTRACE_WITH_REGS > select HAVE_EFFICIENT_UNALIGNED_ACCESS > diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h > index 1494cfa8639b..3a363d6a3bd0 100644 > --- a/arch/arm64/include/asm/ftrace.h > +++ b/arch/arm64/include/asm/ftrace.h > @@ -78,6 +78,16 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr) > return addr; > } > > +static inline void arch_ftrace_set_direct_caller(struct pt_regs *regs, > + unsigned long addr) > +{ > + /* > + * Place custom trampoline address in regs->orig_x0 to let ftrace > + * trampoline jump to it. > + */ > + regs->orig_x0 = addr; > +} > + > #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS > struct dyn_ftrace; > int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec); > diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c > index 1197e7679882..b1ed0bf01c59 100644 > --- a/arch/arm64/kernel/asm-offsets.c > +++ b/arch/arm64/kernel/asm-offsets.c > @@ -80,6 +80,7 @@ int main(void) > DEFINE(S_SDEI_TTBR1, offsetof(struct pt_regs, sdei_ttbr1)); > DEFINE(S_PMR_SAVE, offsetof(struct pt_regs, pmr_save)); > DEFINE(S_STACKFRAME, offsetof(struct pt_regs, stackframe)); > + DEFINE(S_ORIG_X0, offsetof(struct pt_regs, orig_x0)); > DEFINE(PT_REGS_SIZE, sizeof(struct pt_regs)); > BLANK(); > #ifdef CONFIG_COMPAT > diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S > index e535480a4069..b1bd6576f205 100644 > --- a/arch/arm64/kernel/entry-ftrace.S > +++ b/arch/arm64/kernel/entry-ftrace.S > @@ -60,6 +60,9 @@ > str x29, [sp, #S_FP] > .endif > > + /* Set orig_x0 to zero */ > + str xzr, [sp, #S_ORIG_X0] > + > /* Save the callsite's SP and LR */ > add x10, sp, #(PT_REGS_SIZE + 16) > stp x9, x10, [sp, #S_LR] > @@ -119,12 +122,21 @@ ftrace_common_return: > /* Restore the callsite's FP, LR, PC */ > ldr x29, [sp, #S_FP] > ldr x30, [sp, #S_LR] > - ldr x9, [sp, #S_PC] > - > + ldr x10, [sp, #S_PC] > + > + ldr x11, [sp, #S_ORIG_X0] > + cbz x11, 1f > + /* Set x9 to parent ip before jump to bpf trampoline */ > + mov x9, x30 > + /* Set lr to self ip */ > + ldr x30, [sp, #S_PC] > + /* Set x10 (used for return address) to bpf trampoline */ > + mov x10, x11 > +1: > /* Restore the callsite's SP */ > add sp, sp, #PT_REGS_SIZE + 16 > > - ret x9 > + ret x10 > SYM_CODE_END(ftrace_common) > > #ifdef CONFIG_FUNCTION_GRAPH_TRACER > -- > 2.30.2 >
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