linux-kernel - Re: [patch V4 part 4 08/24] x86/entry: Provide IDTENTRY

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Message-ID: <87v9kyxsp3.fsf@nanos.tec.linutronix.de>
Date:   Thu, 14 May 2020 20:44:08 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, X86 ML <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>,
        Steven Rostedt <rostedt@...dmis.org>,
        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 4 08/24] x86/entry: Provide IDTENTRY_IST

Andy Lutomirski <luto@...nel.org> writes:
> On Tue, May 5, 2020 at 7:16 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>>
>> Same as IDTENTRY but for exceptions which run on Interrupt STacks (IST) on
>> 64bit. For 32bit this maps to IDTENTRY.
>>
>> There are 3 variants which will be used:
>>       IDTENTRY_MCE
>>       IDTENTRY_DB
>>       IDTENTRY_NMI
>>
>> These map to IDTENTRY_IST, but only the MCE and DB variants are emitting
>> ASM code as the NMI entry needs hand crafted ASM still.
>>
>> The function defines do not contain any idtenter/exit calls as these
>> exceptions need special treatment.
>
> Okay I guess, but in the long run I'm guessing that we'll want to
> merge a bunch of this to DECLARE_IDTENTRY_NOASM and just manually emit
> the special cases in entry_32/64.S.

The ASM is still the paranoid muck which is emitted nicely.

But on the C side this needs a different treatment than the regular
exceptions which all use idtentry_enter() before and idtentry_exit()
after the handler function body.

Those need magic things before and after nmi_enter/exit(). That's why
the C function is directly called and does not have any automatically
emitted enter/exit stuff like the other IDTENTRY variants.

Thanks,

        tglx