Re: [PATCH 2/3] drivers:hv: Export the API to invoke a hypercall on Hyper-V

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Sep 15, 2015 at 06:26:48PM -0700, K. Y. Srinivasan wrote:
> From: Jake Oshins <jakeo@microsoft.com>
> 
> This patch exposes the function that hv_vmbus.ko uses to make hypercalls.  This
> is necessary for retargeting an interrupt when it is given a new affinity.
> 
> Since we are exporting this API, rename the API as it will be visible outside
> the hv.c file.
> 
> Signed-off-by: Jake Oshins <jakeo@microsoft.com>
> Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
> ---
>  drivers/hv/hv.c        |    9 +++++----
>  include/linux/hyperv.h |    1 +
>  2 files changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
> index 6341be8..a7b6c6a 100644
> --- a/drivers/hv/hv.c
> +++ b/drivers/hv/hv.c
> @@ -89,9 +89,9 @@ static int query_hypervisor_info(void)
>  }
>  
>  /*
> - * do_hypercall- Invoke the specified hypercall
> + * hv_do_hypercall- Invoke the specified hypercall
>   */
> -static u64 do_hypercall(u64 control, void *input, void *output)
> +u64 hv_do_hypercall(u64 control, void *input, void *output)
>  {
>  	u64 input_address = (input) ? virt_to_phys(input) : 0;
>  	u64 output_address = (output) ? virt_to_phys(output) : 0;
> @@ -132,6 +132,7 @@ static u64 do_hypercall(u64 control, void *input, void *output)
>  	return hv_status_lo | ((u64)hv_status_hi << 32);
>  #endif /* !x86_64 */
>  }
> +EXPORT_SYMBOL_GPL(hv_do_hypercall);
>  
>  #ifdef CONFIG_X86_64
>  static cycle_t read_hv_clock_tsc(struct clocksource *arg)
> @@ -329,7 +330,7 @@ int hv_post_message(union hv_connection_id connection_id,
>  	aligned_msg->payload_size = payload_size;
>  	memcpy((void *)aligned_msg->payload, payload, payload_size);
>  
> -	status = do_hypercall(HVCALL_POST_MESSAGE, aligned_msg, NULL)
> +	status = hv_do_hypercall(HVCALL_POST_MESSAGE, aligned_msg, NULL)
>  		& 0xFFFF;
>  
>  	put_cpu();
> @@ -347,7 +348,7 @@ u16 hv_signal_event(void *con_id)
>  {
>  	u16 status;
>  
> -	status = (do_hypercall(HVCALL_SIGNAL_EVENT, con_id, NULL) & 0xFFFF);
> +	status = (hv_do_hypercall(HVCALL_SIGNAL_EVENT, con_id, NULL) & 0xFFFF);

What's with the crazy () around a function call?

And why are you passing a 64bit return value into a 16bit status value?
That seems like something is broken.