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Date:   Wed, 09 Mar 2022 17:05:29 +0530
From:   "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Subject: Re: [PATCH v1 2/4] powerpc/ftrace: Refactor ftrace_{regs_}caller
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Paul Mackerras <paulus@samba.org>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
References: <ec286d2cc6989668a96f14543275437d2f3f0e3a.1645099283.git.christophe.leroy@csgroup.eu>
        <9d7df9e4fc98a86051489f61d3c9bc67f92f7e27.1645099283.git.christophe.leroy@csgroup.eu>
        <1646326634.jzerx009p9.naveen@linux.ibm.com>
        <5c0a3a26-ee52-a4f7-9bc2-b38f27a12a76@csgroup.eu>
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Christophe Leroy wrote:
>=20
>=20
> Le 03/03/2022 =C3=A0 17:59, Naveen N. Rao a =C3=A9crit=C2=A0:
>> Christophe Leroy wrote:
>>
>> The ability to disable ftrace in certain code paths through=20
>> paca_struct->ftrace_enabled will also be relevant on ppc32 - it will be=20
>> nice if it can be introduced there.
>=20
> Ah ? I understood from commit ea678ac627e0 ("powerpc64/ftrace: Add a=20
> field in paca to disable ftrace in unsafe code paths") that it was for=20
> when it runs in real mode. PPC32 doesn't run any C code in real mode.

It likely isn't necessary in that case.

>=20
> Are there any other situations that real_mode where we'd like to disable=20
> 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,=20
mce/hmi and idle/hotplug. If none of those are problematic on ppc32,=20
then this isn't necessary.


Thanks,
- Naveen