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

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Message-ID: <20201019221515.GA2875488@rani.riverdale.lan>
Date:   Mon, 19 Oct 2020 18:15:15 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     shuo.a.liu@...el.com
Cc:     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>, Borislav Petkov <bp@...en8.de>,
        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>,
        Segher Boessenkool <segher@...nel.crashing.org>
Subject: Re: [PATCH v5 04/17] x86/acrn: Introduce hypercall interfaces

On Mon, Oct 19, 2020 at 02:17:50PM +0800, shuo.a.liu@...el.com wrote:
> From: Shuo Liu <shuo.a.liu@...el.com>
> 
> The Service VM communicates with the hypervisor via conventional
> hypercalls. VMCALL instruction is used to make the hypercalls.
> 
> ACRN hypercall ABI:
>   * Hypercall number is in R8 register.
>   * Up to 2 parameters are in RDI and RSI registers.
>   * Return value is in RAX register.
> 
> Introduce the ACRN hypercall interfaces. Because GCC doesn't support R8
> register as direct register constraints, use supported constraint as
> input with a explicit MOV to R8 in beginning of asm.
> 
> +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)

Is the hypercall id an unsigned long (64 bits) or an unsigned int (32
bits)? This will generate broken assembly if the "r" option is chosen,
eg something like
	movl %rdi, %r8d

> +		     : "r8", "memory");
> +
> +	return result;
> +}
> +
> +static inline long acrn_hypercall1(unsigned long hcall_id,
> +				   unsigned long param1)
> +{
> +	long result;
> +
> +	asm volatile("movl %1, %%r8d\n\t"
> +		     "vmcall\n\t"
> +		     : "=a" (result)
> +		     : "ir" (hcall_id), "D" (param1)
> +		     : "r8", "memory");
> +
> +	return result;
> +}
> +
> +static inline long acrn_hypercall2(unsigned long hcall_id,
> +				   unsigned long param1,
> +				   unsigned long param2)
> +{
> +	long result;
> +
> +	asm volatile("movl %1, %%r8d\n\t"
> +		     "vmcall\n\t"
> +		     : "=a" (result)
> +		     : "ir" (hcall_id), "D" (param1), "S" (param2)
> +		     : "r8", "memory");
> +
> +	return result;
> +}
> +
>  #endif /* _ASM_X86_ACRN_H */
> -- 
> 2.28.0
>