linux-kernel - Re: [PATCH -tip v3 1/2] x86: xen: insn: Decode Xen and KVM emulate-prefix signature

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Message-Id: <20190906192822.21afa68b557463fdc7b1cc81@kernel.org>
Date:   Fri, 6 Sep 2019 19:28:22 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org
Subject: Re: [PATCH -tip v3 1/2] x86: xen: insn: Decode Xen and KVM
 emulate-prefix signature

On Fri, 6 Sep 2019 09:34:36 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Fri, Sep 06, 2019 at 10:45:48AM +0900, Masami Hiramatsu wrote:
> 
> > diff --git a/arch/x86/include/asm/xen/interface.h b/arch/x86/include/asm/xen/interface.h
> > index 62ca03ef5c65..fe33a9798708 100644
> > --- a/arch/x86/include/asm/xen/interface.h
> > +++ b/arch/x86/include/asm/xen/interface.h
> > @@ -379,12 +379,15 @@ struct xen_pmu_arch {
> >   * Prefix forces emulation of some non-trapping instructions.
> >   * Currently only CPUID.
> >   */
> > +#include <asm/xen/prefix.h>
> > +
> >  #ifdef __ASSEMBLY__
> > -#define XEN_EMULATE_PREFIX .byte 0x0f,0x0b,0x78,0x65,0x6e ;
> > +#define XEN_EMULATE_PREFIX .byte __XEN_EMULATE_PREFIX ;
> >  #define XEN_CPUID          XEN_EMULATE_PREFIX cpuid
> >  #else
> > -#define XEN_EMULATE_PREFIX ".byte 0x0f,0x0b,0x78,0x65,0x6e ; "
> > +#define XEN_EMULATE_PREFIX ".byte " __XEN_EMULATE_PREFIX_STR " ; "
> >  #define XEN_CPUID          XEN_EMULATE_PREFIX "cpuid"
> > +
> >  #endif
> 
> Possibly you can do something like:
> 
> #define XEN_EMULATE_PREFIX	__ASM_FORM(.byte __XEN_EMULATE_PREFIX ;)
> #define XEN_CPUID		XEN_EMULATE_PREFIX __ASM_FORM(cpuid)

Oops, this doesn't work, since __ASM_FORM(x) uses #x directly

# define __ASM_FORM(x)  " " #x " "

which doesn't expand "x" if x is a macro. We have to use __stringify
like 

# include <linux/stringify.h>
# define __ASM_FORM(x)  " " __stringify(x) " "

So this needs aonther patch in the series :)

Thank you,

-- 
Masami Hiramatsu <mhiramat@...nel.org>