linux-kernel - Re: [RFC][PATCH] objtool,x86_64,paravirt: Add pv

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Message-ID: <CALCETrXhgmkRNaZq9QFWjVVYiX+t=ML_e-oDw2PPEFxQdoA+6Q@mail.gmail.com>
Date:   Mon, 3 Aug 2020 08:15:02 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>, mbenes@...e.de,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Juergen Gross <jgross@...e.com>
Subject: Re: [RFC][PATCH] objtool,x86_64,paravirt: Add pv_ops[] support

On Mon, Aug 3, 2020 at 7:33 AM <peterz@...radead.org> wrote:
>
>
> Thomas wanted paramuck vs noinstr, here goes. Very rough, very nasty,
> mostly works.
>
> It requires call sites are the normal indirect call, and not mangled
> retpoison (slow_down_io() had those), it also requires pv_ops[]
> assignments are single instructions and not laundered through some
> pointless intermediate helper (hyperv).
>
> It doesn't warn when you get any of that wrong.
>
> But if you have it all lined up right, it will warn about noinstr
> violations due to paramuck:

I certainly agree that pv_ops is mucky, but could you expound on
precisely what this patch actually does?  On a very quick
read-through, I'm guessing you're complaining about any call to pv_ops
in a noinstr section?  But maybe this is only calls to pv_ops that
aren't themselves noinstr?