linux-kernel - Re: [PATCH v2 08/13] powerpc/ftrace: Prepare PPC64's ftrace_caller() for CONFIG_DYNAMIC_FTRACE_WITH

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Message-Id: <1644851672.d8a13a7hsf.naveen@linux.ibm.com>
Date:   Mon, 14 Feb 2022 20:49:57 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Jiri Kosina <jikos@...nel.org>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Miroslav Benes <mbenes@...e.cz>,
        Ingo Molnar <mingo@...hat.com>, Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "live-patching@...r.kernel.org" <live-patching@...r.kernel.org>
Subject: Re: [PATCH v2 08/13] powerpc/ftrace: Prepare PPC64's ftrace_caller()
 for CONFIG_DYNAMIC_FTRACE_WITH_ARGS

Hi Christophe,
Thanks for your work enabling DYNAMIC_FTRACE_WITH_ARGS on powerpc. Sorry 
for the late review on this series, but I have a few comments below.


Christophe Leroy wrote:
> In order to implement CONFIG_DYNAMIC_FTRACE_WITH_ARGS, change ftrace_caller()
> to handle LIVEPATCH the same way as frace_caller_regs().
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>  .../powerpc/kernel/trace/ftrace_64_mprofile.S | 25 ++++++++++++++-----
>  1 file changed, 19 insertions(+), 6 deletions(-)

I think we also need to save r1 into pt_regs so that the stack pointer 
is available in the callbacks.

Other than that, a few minor nits below...

> 
> diff --git a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
> index d636fc755f60..f6f787819273 100644
> --- a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
> +++ b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
> @@ -172,14 +172,19 @@ _GLOBAL(ftrace_caller)
>  	addi	r3, r3, function_trace_op@toc@l
>  	ld	r5, 0(r3)
>  
> +#ifdef CONFIG_LIVEPATCH_64
> +	SAVE_GPR(14, r1)
> +	mr	r14,r7		/* remember old NIP */
                    ^ add a space
> +#endif

Please add a blank line here, to match the formatting for the rest of 
this file.

>  	/* 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 */
> +	std	r0, _LINK(r1)
>  	mr	r4, r0
>  
> -	/* Set pt_regs to NULL */
> -	li	r6, 0
> +	/* Load &pt_regs in r6 for call below */
> +	addi    r6, r1 ,STACK_FRAME_OVERHEAD
                      ^^ incorrect spacing
>  
>  	/* ftrace_call(r3, r4, r5, r6) */
>  .globl ftrace_call
> @@ -189,6 +194,10 @@ ftrace_call:
>  
>  	ld	r3, _NIP(r1)
>  	mtctr	r3

Another blank line here.

> +#ifdef CONFIG_LIVEPATCH_64
> +	cmpd	r14, r3		/* has NIP been altered? */
> +	REST_GPR(14, r1)
> +#endif
>  
>  	/* Restore gprs */
>  	REST_GPRS(3, 10, r1)
> @@ -196,13 +205,17 @@ ftrace_call:
>  	/* Restore callee's TOC */
>  	ld	r2, 24(r1)
>  
> +	/* Restore possibly modified LR */
> +	ld	r0, _LINK(r1)
> +	mtlr	r0
> +
>  	/* Pop our stack frame */
>  	addi	r1, r1, SWITCH_FRAME_SIZE
>  
> -	/* Reload original LR */
> -	ld	r0, LRSAVE(r1)
> -	mtlr	r0
> -
> +#ifdef CONFIG_LIVEPATCH_64
> +        /* Based on the cmpd above, if the NIP was altered handle livepatch */
> +	bne-	livepatch_handler
> +#endif

Here too.

>  	/* Handle function_graph or go back */
>  	b	ftrace_caller_common
>  


- Naveen