linux-kernel - Re: [patch V4 part 3 17/29] x86/entry: Convert Invalid Opcode exception to IDTENTRY

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Date:   Wed, 13 May 2020 21:45:02 -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>
Subject: Re: [patch V4 part 3 17/29] x86/entry: Convert Invalid Opcode
 exception to IDTENTRY

On Tue, May 5, 2020 at 7:15 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> From: Thomas Gleixner <tglx@...utronix.de>
>
> Convert #UD to IDTENTRY:
>   - Implement the C entry point with DEFINE_IDTENTRY
>   - Emit the ASM stub with DECLARE_IDTENTRY
>   - Remove the ASM idtentry in 64bit
>   - Remove the open coded ASM entry code in 32bit
>   - Fixup the XEN/PV code
>   - Fixup the FOOF bug call in fault.c
>   - Remove the old prototyoes
>
> No functional change.

I think there *is* a functional change:


> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -567,7 +567,7 @@ static int is_f00f_bug(struct pt_regs *r
>                 nr = (address - idt_descr.address) >> 3;
>
>                 if (nr == 6) {
> -                       do_invalid_op(regs, 0);
> +                       handle_invalid_op(regs);

I suspect the old code was wrong and no one noticed because no one has
a F00F-buggy machine any more.

So maybe document that you fixed up the F00F bug, too.  Otherwise:


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