linux-kernel - Re: [tip: core/kprobes] arm/ftrace: Use __patch

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Date:   Fri, 7 Feb 2020 12:27:20 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        tip-bot2 for Peter Zijlstra <tip-bot2@...utronix.de>,
        linux-tip-commits@...r.kernel.org, Will Deacon <will@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jon Hunter <jonathanh@...dia.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mark Rutland <mark.rutland@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        ard.biesheuvel@...aro.org, james.morse@....com, rabin@....in,
        Ingo Molnar <mingo@...nel.org>, x86 <x86@...nel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [tip: core/kprobes] arm/ftrace: Use __patch_text()

On Thu, Jan 23, 2020 at 12:26:46AM +0300, Dmitry Osipenko wrote:
> 04.12.2019 11:33, tip-bot2 for Peter Zijlstra пишет:
> > @@ -97,10 +94,7 @@ static int ftrace_modify_code(unsigned long pc, unsigned long old,
> >  			return -EINVAL;
> >  	}
> >  
> > -	if (probe_kernel_write((void *)pc, &new, MCOUNT_INSN_SIZE))
> > -		return -EPERM;
> > -
> > -	flush_icache_range(pc, pc + MCOUNT_INSN_SIZE);
> > +	__patch_text((void *)pc, new);
> >  
> >  	return 0;
> >  }
> > 
> 
> Hello,
> 
> NVIDIA Tegra20/30 are not booting with CONFIG_FTRACE=y, but even with
> CONFIG_FTRACE=n things are not working well.

Ooh, I think I see. Can you try this:

diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
index 2a5ff69c28e6..10499d44964a 100644
--- a/arch/arm/kernel/ftrace.c
+++ b/arch/arm/kernel/ftrace.c
@@ -78,13 +78,10 @@ static int ftrace_modify_code(unsigned long pc, unsigned long old,
 {
 	unsigned long replaced;
 
-	if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
+	if (IS_ENABLED(CONFIG_THUMB2_KERNEL))
 		old = __opcode_to_mem_thumb32(old);
-		new = __opcode_to_mem_thumb32(new);
-	} else {
+	else
 		old = __opcode_to_mem_arm(old);
-		new = __opcode_to_mem_arm(new);
-	}
 
 	if (validate) {
 		if (probe_kernel_read(&replaced, (void *)pc, MCOUNT_INSN_SIZE))