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Date:   Mon, 2 Nov 2020 10:09:01 -0600
From:   Segher Boessenkool <segher@kernel.crashing.org>
To:     Borislav Petkov <bp@alien8.de>
Cc:     shuo.a.liu@intel.com, linux-kernel@vger.kernel.org, x86@kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Yu Wang <yu1.wang@intel.com>,
        Reinette Chatre <reinette.chatre@intel.com>,
        Yakui Zhao <yakui.zhao@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Fengwei Yin <fengwei.yin@intel.com>,
        Zhi Wang <zhi.a.wang@intel.com>,
        Zhenyu Wang <zhenyuw@linux.intel.com>,
        Arvind Sankar <nivedita@alum.mit.edu>,
        Peter Zijlstra <peterz@infradead.org>,
        Nick Desaulniers <ndesaulniers@google.com>
Subject: Re: [PATCH v5 04/17] x86/acrn: Introduce hypercall interfaces
Message-ID: <20201102160901.GU2672@gate.crashing.org>
References: <20201019061803.13298-1-shuo.a.liu@intel.com> <20201019061803.13298-5-shuo.a.liu@intel.com> <20201102145657.GD15392@zn.tnic>
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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@intel.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