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

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Message-ID: <20190906091510.GV2349@hirez.programming.kicks-ass.net>
Date:   Fri, 6 Sep 2019 11:15:10 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Masami Hiramatsu <mhiramat@...nel.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, Sep 06, 2019 at 05:51:43PM +0900, Masami Hiramatsu wrote:
> On Fri, 6 Sep 2019 17:45:19 +0900
> Masami Hiramatsu <mhiramat@...nel.org> wrote:
> 
> > > 
> > > How about we make this asm/virt_prefix.h or something and include:
> > > 
> > > /*
> > >  * Virt escape sequences to trigger instruction emulation;
> > >  * ideally these would decode to 'whole' instruction and not destroy
> > >  * the instruction stream; sadly this is not true for the 'kvm' one :/
> > >  */
> > > 
> > > #define __XEN_EMULATE_PREFIX  0x0f,0x0b,0x78,0x65,0x6e  /* ud2 ; .ascii "xen" */
> > > #define __KVM_EMULATE_PREFIX  0x0f,0x0b,0x6b,0x76,0x6d	/* ud2 ; .ascii "kvm" */
> 
> BTW, what should we call it, "emulate prefix" or "virt prefix"?
> "virt prefix" sounds too generic to me. So I rather like emulate_prefix.h.

Works for me; and yeah, just see what is best for the other things. I
only started down that road because the Xen and KVM 'prefixes' were
initialized so inconsistently.