linux-kernel - Re: [PATCH v5 04/17] x86/acrn: Introduce hypercall interfaces

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Message-ID: <20201102160901.GU2672@gate.crashing.org>
Date:   Mon, 2 Nov 2020 10:09:01 -0600
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     shuo.a.liu@...el.com, linux-kernel@...r.kernel.org, x86@...nel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Yu Wang <yu1.wang@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Yakui Zhao <yakui.zhao@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Fengwei Yin <fengwei.yin@...el.com>,
        Zhi Wang <zhi.a.wang@...el.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Peter Zijlstra <peterz@...radead.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH v5 04/17] x86/acrn: Introduce hypercall interfaces

On Mon, Nov 02, 2020 at 03:56:57PM +0100, Borislav Petkov wrote:
> On Mon, Oct 19, 2020 at 02:17:50PM +0800, shuo.a.liu@...el.com wrote:
> > +static inline long acrn_hypercall0(unsigned long hcall_id)
> > +{
> > +	long result;
> > +
> > +	asm volatile("movl %1, %%r8d\n\t"
> > +		     "vmcall\n\t"
> > +		     : "=a" (result)
> > +		     : "ir" (hcall_id)
> 			^^
> 
> Not "irm"? Or simply "g" in that case?

I think that will work for x86_64.  But it won't matter much, most of
the time you give an immediate number.  It is a tiny bit neater of
course (if anyone still remembers what "g" is, you cannot use it much
these days).


Segher