Re: [PATCH v3 04/10] x86/hyper-v: fast hypercall implementation

[Andy Lutomirski <luto@kernel.org>]

On 05/19/2017 07:09 AM, Vitaly Kuznetsov wrote:
> Hyper-V supports 'fast' hypercalls when all parameters are passed through
> registers. Implement an inline version of a simpliest of these calls:
> hypercall with one 8-byte input and no output.
> 
> Proper hypercall input interface (struct hv_hypercall_input) definition is
> added as well.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> Acked-by: K. Y. Srinivasan <kys@microsoft.com>
> Tested-by: Simon Xiao <sixiao@microsoft.com>
> Tested-by: Srikanth Myakam <v-srm@microsoft.com>
> ---
>   arch/x86/include/asm/mshyperv.h    | 39 ++++++++++++++++++++++++++++++++++++++
>   arch/x86/include/uapi/asm/hyperv.h | 19 +++++++++++++++++++
>   2 files changed, 58 insertions(+)
> 
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index e293937..028e29b 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -216,6 +216,45 @@ static inline u64 hv_do_hypercall(u64 control, void *input, void *output)
>   #endif /* !x86_64 */
>   }
>   
> +/* Fast hypercall with 8 bytes of input and no output */
> +static inline u64 hv_do_fast_hypercall8(u16 code, u64 input1)
> +{
> +	union hv_hypercall_input control = {0};
> +
> +	control.code = code;
> +	control.fast = 1;
> +#ifdef CONFIG_X86_64
> +	{
> +		u64 hv_status;
> +
> +		__asm__ __volatile__("call *%3"
> +				     : "=a" (hv_status),
> +				       "+c" (control.as_uint64), "+d" (input1)
> +				     : "m" (hv_hypercall_pg)
> +				     : "cc", "r8", "r9", "r10", "r11");
> +		return hv_status;
> +	}
> +#else
> +	{
> +		u32 hv_status_hi, hv_status_lo;
> +		u32 input1_hi = (u32)(input1 >> 32);
> +		u32 input1_lo = (u32)input1;
> +
> +		__asm__ __volatile__ ("call *%6"
> +				      : "=d"(hv_status_hi),
> +					"=a"(hv_status_lo),
> +					"+c"(input1_lo)
> +				      :	"d" (control.as_uint32_hi),
> +					"a" (control.as_uint32_lo),
> +					"b" (input1_hi),
> +					"m" (hv_hypercall_pg)
> +				      : "cc", "edi", "esi");
> +
> +		return hv_status_lo | ((u64)hv_status_hi << 32);
> +	}
> +#endif

This is going to need an explicit "sp" annotation to force a stack 
frame, I think.  Otherwise objtool is likely to get mad in a 
frame-pointer-omitted build.