linux-kernel - Re: [patch V6 21/37] x86/entry: Add IRQENTRY

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Message-ID: <CALCETrWNBNCuNv==ZTBom5+X-Wyp+4_tsy=C_at-orv=0H3kuA@mail.gmail.com>
Date:   Tue, 19 May 2020 13:27:43 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
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>,
        Tom Lendacky <thomas.lendacky@....com>,
        Wei Liu <wei.liu@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Jason Chen CJ <jason.cj.chen@...el.com>,
        Zhao Yakui <yakui.zhao@...el.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [patch V6 21/37] x86/entry: Add IRQENTRY_IRQ macro

On Fri, May 15, 2020 at 5:10 PM Thomas Gleixner <tglx@...utronix.de> wrote:
>
>
> Provide a seperate IDTENTRY macro for device interrupts. Similar to
> IDTENTRY_ERRORCODE with the addition of invoking irq_enter/exit_rcu() and
> providing the errorcode as a 'u8' argument to the C function, which
> truncates the sign extended vector number.

Acked-by: Andy Lutomirski <luto@...nel.org>

with a minor minor optimization suggestion:

> +.macro idtentry_irq vector cfunc
> +       .p2align CONFIG_X86_L1_CACHE_SHIFT
> +SYM_CODE_START_LOCAL(asm_\cfunc)
> +       ASM_CLAC
> +       SAVE_ALL switch_stacks=1
> +       ENCODE_FRAME_POINTER
> +       movl    %esp, %eax
> +       movl    PT_ORIG_EAX(%esp), %edx         /* get the vector from stack */

You could save somewhere between 0 and 1 cycles by using movzbl here...

> +       __##func (regs, (u8)error_code);                                \

And eliminating this cast.  Totally worth it, right?