linux-kernel - Re: [PATCH v2 09/13] powerpc/ftrace: Implement CONFIG_DYNAMIC_FTRACE_WITH

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Message-ID: <yt9dmtir3psi.fsf@linux.ibm.com>
Date:   Wed, 16 Feb 2022 14:27:09 +0100
From:   Sven Schnelle <svens@...ux.ibm.com>
To:     Heiko Carstens <hca@...ux.ibm.com>
Cc:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Jiri Kosina <jikos@...nel.org>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Miroslav Benes <mbenes@...e.cz>,
        Ingo Molnar <mingo@...hat.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "live-patching@...r.kernel.org" <live-patching@...r.kernel.org>
Subject: Re: [PATCH v2 09/13] powerpc/ftrace: Implement
 CONFIG_DYNAMIC_FTRACE_WITH_ARGS

Heiko Carstens <hca@...ux.ibm.com> writes:

> So, the in both variants s390 provides nearly identical data. The only
> difference is that for FL_SAVE_REGS the program status word mask is
> missing; therefore it is not possible to figure out the condition code
> or if interrupts were enabled/disabled.
>
> Vasily, Sven, I think we have two options here:
>
> - don't provide sane psw mask contents at all and say (again) that
>   ptregs contents are identical
>
> - provide (finally) a full psw mask contents using epsw, and indicate
>   validity with a flags bit in pt_regs
>
> I would vote for the second option, even though epsw is slow. But this
> is about the third or fourth time this came up in different
> contexts. So I'd guess we should go for the slow but complete
> solution. Opinions?

Given that this only affects ftrace_regs_caller, i would also vote for the
second option.