linux-kernel - Re: [PATCH v1 2/4] powerpc/ftrace: Refactor ftrace_{regs

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Message-Id: <1646825481.p25t8oi12m.naveen@linux.ibm.com>
Date:   Wed, 09 Mar 2022 17:05:29 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v1 2/4] powerpc/ftrace: Refactor ftrace_{regs_}caller

Christophe Leroy wrote:
> 
> 
> Le 03/03/2022 à 17:59, Naveen N. Rao a écrit :
>> Christophe Leroy wrote:
>>
>> The ability to disable ftrace in certain code paths through 
>> paca_struct->ftrace_enabled will also be relevant on ppc32 - it will be 
>> nice if it can be introduced there.
> 
> Ah ? I understood from commit ea678ac627e0 ("powerpc64/ftrace: Add a 
> field in paca to disable ftrace in unsafe code paths") that it was for 
> when it runs in real mode. PPC32 doesn't run any C code in real mode.

It likely isn't necessary in that case.

> 
> Are there any other situations that real_mode where we'd like to disable 
> it ? If so we could use the thread_struct as we don't have paca on PPC32.

For ppc64, we use this flag to disable certain paths in kvm, kexec, 
mce/hmi and idle/hotplug. If none of those are problematic on ppc32, 
then this isn't necessary.


Thanks,
- Naveen