linux-kernel - Re: [patch V4 part 3 09/29] x86/entry/32: Provide macro to emit IDT entry stubs

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Message-ID: <87eermzk1n.fsf@nanos.tec.linutronix.de>
Date:   Thu, 14 May 2020 16:08:04 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Andy Lutomirski <luto@...nel.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>,
        paulmck <paulmck@...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>, rostedt <rostedt@...dmis.org>,
        "Joel Fernandes\, Google" <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>
Subject: Re: [patch V4 part 3 09/29] x86/entry/32: Provide macro to emit IDT entry stubs

Mathieu Desnoyers <mathieu.desnoyers@...icios.com> writes:
> ----- On May 14, 2020, at 12:31 AM, Andy Lutomirski luto@...nel.org wrote:
>> On Wed, May 13, 2020 at 6:44 PM Mathieu Desnoyers
>> <mathieu.desnoyers@...icios.com> wrote:
>> They're needed for all entries except SYSCALL, but they're hidden
>> inside helpers in many cases.
>
> Indeed, on x86-32 the macro SAVE_ALL contains cld. That architecture
> appears to be OK.
>
> What I am concerned about is the idtentry, idtentry_mce_db,
> and idtentry_df macros introduced in entry_64.S by this series.
> Those are supposed to be technically equivalent to the prior
> code, which indeed has the ASM_CLAC but no "cld".
>
> So maybe the cld happens to be hidden elsewhere, but I'm clearly
> missing it ? Or is it not needed for some reason ?

It's needed and it is there where it was forever in error_entry and
paranoid_entry.

It probably makes sense to stick it right after the CLAC.

Thanks,

        tglx