linux-kernel - Re: [PATCH v4 05/10] hyper-v: use fast hypercall for HVCALL_SIGNAL

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Date:   Sat, 27 May 2017 20:50:33 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     devel@...uxdriverproject.org, "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Jork Loeser <Jork.Loeser@...rosoft.com>,
        Simon Xiao <sixiao@...rosoft.com>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v4 05/10] hyper-v: use fast hypercall for HVCALL_SIGNAL_EVENT

On Wed, May 24, 2017 at 3:04 PM, Vitaly Kuznetsov <vkuznets@...hat.com> wrote:
> We need to pass only 8 bytes of input for HvSignalEvent which makes it a
> perfect fit for fast hypercall. hv_input_signal_event_buffer is not needed
> any more and hv_input_signal_event is converted to union for convenience.

> +union hv_input_signal_event {

Union aliasing is UB. Avoid it for good.

> +       u64 as_uint64;
> +       struct {
> +               union hv_connection_id connectionid;
> +               u16 flag_number;
> +               u16 rsvdz;
> +       };
>  };

-- 
With Best Regards,
Andy Shevchenko