linux-kernel - Re: [patch V4 part 2 10/18] x86/entry/64: Check IF in __preempt_enable

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Message-ID: <20200511215108.3ccea526@oasis.local.home>
Date:   Mon, 11 May 2020 21:51:08 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>
Subject: Re: [patch V4 part 2 10/18] x86/entry/64: Check IF in
 __preempt_enable_notrace() thunk

On Tue, 05 May 2020 15:41:22 +0200
Thomas Gleixner <tglx@...utronix.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....

Config attached.

-- Steve


Download attachment "config.gz" of type "application/gzip" (34653 bytes)