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

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Date:	Mon, 21 Sep 2015 09:41:28 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	KY Srinivasan <kys@...rosoft.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"vkuznets@...hat.com" <vkuznets@...hat.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	Jake Oshins <jakeo@...rosoft.com>
Subject: Re: [PATCH 2/3] drivers:hv: Export the API to invoke a hypercall on
 Hyper-V

On Mon, Sep 21, 2015 at 04:22:01PM +0000, KY Srinivasan wrote:
> 
> 
> > -----Original Message-----
> > From: Greg KH [mailto:gregkh@...uxfoundation.org]
> > Sent: Sunday, September 20, 2015 10:28 PM
> > To: KY Srinivasan <kys@...rosoft.com>
> > Cc: linux-kernel@...r.kernel.org; devel@...uxdriverproject.org;
> > olaf@...fle.de; apw@...onical.com; vkuznets@...hat.com;
> > jasowang@...hat.com; Jake Oshins <jakeo@...rosoft.com>
> > Subject: Re: [PATCH 2/3] drivers:hv: Export the API to invoke a hypercall on
> > Hyper-V
> > 
> > On Tue, Sep 15, 2015 at 06:26:48PM -0700, K. Y. Srinivasan wrote:
> > > From: Jake Oshins <jakeo@...rosoft.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@...rosoft.com>
> > > Signed-off-by: K. Y. Srinivasan <kys@...rosoft.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?
> 
> I will address this and resend.
> > 
> > And why are you passing a 64bit return value into a 16bit status value?
> > That seems like something is broken.
> 
> The low order 16 bits have the valid status codes we are interested in.

Then why even return a 64bit number if no one uses it?

greg k-h
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