linux-kernel - Re: [PATCH 3/3 v7] livepatch: Use the default ftrace_ops instead of REGS when ARGS is available

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Date:   Thu, 19 Nov 2020 12:52:00 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>, live-patching@...r.kernel.org
Subject: Re: [PATCH 3/3 v7] livepatch: Use the default ftrace_ops instead of
 REGS when ARGS is available

On Fri 2020-11-13 12:18:14, Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> 
> When CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS is available, the ftrace call
> will be able to set the ip of the calling function. This will improve the
> performance of live kernel patching where it does not need all the regs to
> be stored just to change the instruction pointer.
> 
> If all archs that support live kernel patching also support
> HAVE_DYNAMIC_FTRACE_WITH_ARGS, then the architecture specific function
> klp_arch_set_pc() could be made generic.
> 
> It is possible that an arch can support HAVE_DYNAMIC_FTRACE_WITH_ARGS but
> not HAVE_DYNAMIC_FTRACE_WITH_REGS and then have access to live patching.
> 
> Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> Cc: Jiri Kosina <jikos@...nel.org>
> Cc: live-patching@...r.kernel.org
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Acked-by: Miroslav Benes <mbenes@...e.cz>
> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> ---
> Changes since v6:
>  - Updated to use ftrace_instruction_pointer_set() macro
> 
>  arch/powerpc/include/asm/livepatch.h | 4 +++-
>  arch/s390/include/asm/livepatch.h    | 5 ++++-
>  arch/x86/include/asm/ftrace.h        | 3 +++
>  arch/x86/include/asm/livepatch.h     | 4 ++--
>  arch/x86/kernel/ftrace_64.S          | 4 ++++
>  include/linux/ftrace.h               | 7 +++++++
>  kernel/livepatch/Kconfig             | 2 +-
>  kernel/livepatch/patch.c             | 9 +++++----
>  8 files changed, 29 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/livepatch.h b/arch/powerpc/include/asm/livepatch.h
> index 4a3d5d25fed5..ae25e6e72997 100644
> --- a/arch/powerpc/include/asm/livepatch.h
> +++ b/arch/powerpc/include/asm/livepatch.h
> @@ -12,8 +12,10 @@
>  #include <linux/sched/task_stack.h>
>  
>  #ifdef CONFIG_LIVEPATCH
> -static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
> +static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned long ip)
>  {
> +	struct pt_regs *regs = ftrace_get_regs(fregs);

Should we check for NULL pointer here?

> +
>  	regs->nip = ip;
>  }
>  
> diff --git a/arch/s390/include/asm/livepatch.h b/arch/s390/include/asm/livepatch.h
> index 818612b784cd..d578a8c76676 100644
> --- a/arch/s390/include/asm/livepatch.h
> +++ b/arch/s390/include/asm/livepatch.h
> @@ -11,10 +11,13 @@
>  #ifndef ASM_LIVEPATCH_H
>  #define ASM_LIVEPATCH_H
>  
> +#include <linux/ftrace.h>
>  #include <asm/ptrace.h>
>  
> -static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
> +static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned long ip)
>  {
> +	struct pt_regs *regs = ftrace_get_regs(fregs);

And here?

> +
>  	regs->psw.addr = ip;
>  }
>  

Otherwise, it looks for me.

Best Regards,
Petr