linux-kernel - Re: [PATCH 2/4] x86/vmware: Add a header file for hypercall definitions

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Date:   Tue, 20 Aug 2019 15:42:57 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Thomas Hellström (VMware) 
        <thomas_os@...pmail.org>
cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, pv-drivers@...are.com,
        Thomas Hellstrom <thellstrom@...are.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Doug Covelli <dcovelli@...are.com>
Subject: Re: [PATCH 2/4] x86/vmware: Add a header file for hypercall
 definitions

On Tue, 20 Aug 2019, Thomas Hellström (VMware) wrote:

> On 8/20/19 1:32 PM, Peter Zijlstra wrote:
> > On Sun, Aug 18, 2019 at 04:33:14PM +0200, Thomas Hellström (VMware) wrote:
> > 
> > > +#define VMWARE_HYPERCALL \
> > > +	ALTERNATIVE_2(".byte 0xed", \
> > > +		      ".byte 0x0f, 0x01, 0xc1", X86_FEATURE_VMW_VMCALL,	\
> > > +		      ".byte 0x0f, 0x01, 0xd9", X86_FEATURE_VMW_VMMCALL)
> > For sanity, could we either add comments, or macros for those
> > instrucions?
> 
> Hmm. Here I followed and slightly extended what was done in asm/kvm_para.h.
> 
> What confuses me a bit is, if it's clarity we're after, why don't people use
> 
> #define VMWARE_HYPERCALL 					\
> 	ALTERNATIVE_2("inl (%%dx)", 				\
> 		      "vmcall", X86_FEATURE_VMW_VMCALL,		\	
> 		      "vmmcall", X86_FEATURE_VMW_VMMCALL)
> 
> Seems to build fine here. Is it fear of old assemblers not supporting, for
> example vmmcall

The requirement for binutils is version >= 2.21. If 2.21 supports vmcall and
vmmcall all good.

Thanks,

	tglx