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

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Message-ID: <BY2PR0301MB165418D610D54B6085C1719EA0460@BY2PR0301MB1654.namprd03.prod.outlook.com>
Date:	Mon, 21 Sep 2015 16:22:01 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Greg KH <gregkh@...uxfoundation.org>
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



> -----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.

K. Y



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