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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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