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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Andy Lutomirski <luto@kernel.org>,
        Alexandre Chartre <alexandre.chartre@oracle.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Petr Mladek <pmladek@suse.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        Brian Gerst <brgerst@gmail.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Will Deacon <will@kernel.org>
Subject: Re: [patch V4 part 2 10/18] x86/entry/64: Check IF in __preempt_enable_notrace() thunk
In-Reply-To: <20200511215108.3ccea526@oasis.local.home>
References: <20200505134112.272268764@linutronix.de> <20200505134341.087595319@linutronix.de> <20200511215108.3ccea526@oasis.local.home>
Date:   Tue, 12 May 2020 10:14:04 +0200
Message-ID: <87blmt604z.fsf@nanos.tec.linutronix.de>
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Steven Rostedt <rostedt@goodmis.org> writes:
> On Tue, 05 May 2020 15:41:22 +0200
> Thomas Gleixner <tglx@linutronix.de> wrote:
>
>> The preempt_enable_notrace() ASM thunk is called from tracing, entry code
>> RCU and other places which are already in or going to be in the noinstr
>> section which protects sensitve code from being instrumented.
>> 
>> Calls out of these sections happen with interrupts disabled, which is
>> handled in C code, but the push regs, call, pop regs sequence can be
>> completely avoided in this case.
>> 
>> This is also a preparatory step for annotating the call from the thunk to
>> preempt_enable_notrace() safe from a noinstr section.
>> 
>
> BTW, after applying this patch, I get the following error:
>
> /work/git/linux-test.git/arch/x86/entry/thunk_64.S: Assembler messages:
> /work/git/linux-test.git/arch/x86/entry/thunk_64.S:67: Error: invalid operands (*UND* and *UND* sections) for `+'
> /work/git/linux-test.git/arch/x86/entry/thunk_64.S:67: Error: invalid operands (*UND* and *ABS* sections) for `/'
> make[3]: *** [/work/git/linux-test.git/scripts/Makefile.build:349: arch/x86/entry/thunk_64.o] Error 1
> make[3]: *** Waiting for unfinished jobs....

Yes I know, but I'm going to drop that patch completely.