linux-kernel - Re: [PATCH 03/24] x86/paravirt: Annotate indirect calls

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Message-ID: <20180129181717.GX2269@hirez.programming.kicks-ass.net>
Date:   Mon, 29 Jan 2018 19:17:17 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, Dave Hansen <dave.hansen@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Jason Baron <jbaron@...mai.com>
Subject: Re: [PATCH 03/24] x86/paravirt: Annotate indirect calls

On Mon, Jan 29, 2018 at 11:58:58AM -0600, Josh Poimboeuf wrote:
> On Tue, Jan 23, 2018 at 04:25:42PM +0100, Peter Zijlstra wrote:
> > Paravirt emits indirect calls which get flagged by objtool retpoline
> > checks, annotate it away because all these indirect calls will be
> > patched out before we start userspace.
> > 
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > ---
> >  arch/x86/include/asm/paravirt.h       |   22 ++++++++++++++++++----
> >  arch/x86/include/asm/paravirt_types.h |    7 ++++++-
> >  2 files changed, 24 insertions(+), 5 deletions(-)
> > 
> > --- a/arch/x86/include/asm/paravirt.h
> > +++ b/arch/x86/include/asm/paravirt.h
> > @@ -828,6 +828,12 @@ extern void default_banner(void);
> >  	 .short clobbers;			\
> >  	.popsection
> >  
> > +#define PARA_RETPOLINE_SAFE				\
> > +	773:;						\
> > +	.pushsection .discard.retpoline_safe;		\
> > +	_ASM_PTR 773b;					\
> > +	.popsection
> 
> Why does paravirt have its own version of this macro?

Every time I touch paravirt.h I land in header hell :/ Maybe it can be
made to work, but I was too scared to try this time.