Re: [PATCH v4 03/10] x86/hyper-v: make hv_do_hypercall() inline

From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: devel@linuxdriverproject.org, "x86@kernel.org" <x86@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"K. Y. Srinivasan" <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Jork Loeser <Jork.Loeser@microsoft.com>,
	Simon Xiao <sixiao@microsoft.com>,
	Andy Lutomirski <luto@kernel.org>
Subject: Re: [PATCH v4 03/10] x86/hyper-v: make hv_do_hypercall() inline
Date: Sat, 27 May 2017 20:46:30 +0300	[thread overview]
Message-ID: <CAHp75Vd9vcXUj7g2MVc0x1Xr9Y9yuYcxxHS2XQ_5Wvof9Ug=zA@mail.gmail.com> (raw)
In-Reply-To: <20170524120405.19079-4-vkuznets@redhat.com>

On Wed, May 24, 2017 at 3:03 PM, Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
> We have only three call sites for hv_do_hypercall() and we're going to
> change HVCALL_SIGNAL_EVENT to doing fast hypercall so we can inline this
> function for optimization.
>
> Hyper-V top level functional specification states that r9-r11 registers
> and flags may be clobbered by the hypervisor during hypercall and with
> inlining this is somewhat important, add the clobbers.

> +       u32 control_hi = control >> 32;
> +       u32 control_lo = control & 0xFFFFFFFF;
> +       u32 input_address_hi = input_address >> 32;
> +       u32 input_address_lo = input_address & 0xFFFFFFFF;
> +       u32 output_address_hi = output_address >> 32;
> +       u32 output_address_lo = output_address & 0xFFFFFFFF;

Yes, I have noticed it was in older code, but see, all conjunctions
above are redundant.

Besides that, you may consider to use upper_32_bits() / lower_32_bits() macros.

-- 
With Best Regards,
Andy Shevchenko