linux-kernel - Re: [PATCH -v5 13/17] arm/ftrace: Use __patch_text

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Message-ID: <20191112112950.GB17835@willie-the-truck>
Date:   Tue, 12 Nov 2019 11:29:51 +0000
From:   Will Deacon <will@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, rostedt@...dmis.org,
        mhiramat@...nel.org, bristot@...hat.com, jbaron@...mai.com,
        torvalds@...ux-foundation.org, tglx@...utronix.de,
        mingo@...nel.org, namit@...are.com, hpa@...or.com, luto@...nel.org,
        ard.biesheuvel@...aro.org, jpoimboe@...hat.com, jeyu@...nel.org,
        alexei.starovoitov@...il.com, rabin@....in,
        Mark Rutland <mark.rutland@....com>, james.morse@....com
Subject: Re: [PATCH -v5 13/17] arm/ftrace: Use __patch_text_real()

On Mon, Nov 11, 2019 at 06:25:41PM +0100, Peter Zijlstra wrote:
> On Mon, Nov 11, 2019 at 06:19:55PM +0100, Peter Zijlstra wrote:
> 
> > If you can give me a Tested-by, I'll replace it with the below... :-)
> > 
> > --- a/arch/arm/kernel/ftrace.c
> > +++ b/arch/arm/kernel/ftrace.c
> > @@ -22,6 +22,7 @@
> >  #include <asm/ftrace.h>
> >  #include <asm/insn.h>
> >  #include <asm/set_memory.h>
> > +#include <asm/patch.h>
> >  
> >  #ifdef CONFIG_THUMB2_KERNEL
> >  #define	NOP		0xf85deb04	/* pop.w {lr} */
> > @@ -35,9 +36,7 @@ static int __ftrace_modify_code(void *da
> >  {
> >  	int *command = data;
> >  
> > -	set_kernel_text_rw();
> >  	ftrace_modify_all_code(*command);
> > -	set_kernel_text_ro();
> >  
> >  	return 0;
> >  }
> > @@ -59,13 +58,11 @@ static unsigned long adjust_address(stru
> >  
> >  int ftrace_arch_code_modify_prepare(void)
> >  {
> > -	set_all_modules_text_rw();
> >  	return 0;
> >  }
> >  
> >  int ftrace_arch_code_modify_post_process(void)
> >  {
> > -	set_all_modules_text_ro();
> >  	/* Make sure any TLB misses during machine stop are cleared. */
> >  	flush_tlb_all();
> >  	return 0;
> > @@ -97,10 +94,7 @@ static int ftrace_modify_code(unsigned l
> >  			return -EINVAL;
> >  	}
> >  
> > -	if (probe_kernel_write((void *)pc, &new, MCOUNT_INSN_SIZE))
> > -		return -EPERM;
> > -
> > -	flush_icache_range(pc, pc + MCOUNT_INSN_SIZE);
> > +	__patch_text_real((void *)pc, new, true);
> 
> I'll even make that: __patch_text((void *)pc, new);

This fails to compile. I bodged it as below, but maybe this stuff should
actually live in insn.c. Not fussed either way. I ran the ftrace tests,
loaded a module and toggled ftrace on/off with this applied and it looks
like it works to me:

Tested-by: Will Deacon <will@...nel.org>

Will

--->8

diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 8cad59465af3..a885172e504c 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -49,8 +49,8 @@ obj-$(CONFIG_HAVE_ARM_SCU)	+= smp_scu.o
 obj-$(CONFIG_HAVE_ARM_TWD)	+= smp_twd.o
 obj-$(CONFIG_ARM_ARCH_TIMER)	+= arch_timer.o
 obj-$(CONFIG_FUNCTION_TRACER)	+= entry-ftrace.o
-obj-$(CONFIG_DYNAMIC_FTRACE)	+= ftrace.o insn.o
-obj-$(CONFIG_FUNCTION_GRAPH_TRACER)	+= ftrace.o insn.o
+obj-$(CONFIG_DYNAMIC_FTRACE)	+= ftrace.o insn.o patch.o
+obj-$(CONFIG_FUNCTION_GRAPH_TRACER)	+= ftrace.o insn.o patch.o
 obj-$(CONFIG_JUMP_LABEL)	+= jump_label.o insn.o patch.o
 obj-$(CONFIG_KEXEC)		+= machine_kexec.o relocate_kernel.o
 # Main staffs in KPROBES are in arch/arm/probes/ .