linux-kernel - Re: [PATCH -next] x86: Fix unused variable 'msr

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Message-ID: <20210322110437.ei3vfove4xqky3h5@liuwe-devbox-debian-v2>
Date:   Mon, 22 Mar 2021 11:04:37 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Xu Yihang <xuyihang@...wei.com>
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        johnny.chenyi@...wei.com, heying24@...wei.com,
        Wei Liu <wei.liu@...nel.org>
Subject: Re: [PATCH -next] x86: Fix unused variable 'msr_val' warning

On Mon, Mar 22, 2021 at 11:17:13AM +0800, Xu Yihang wrote:
> Fixes the following W=1 kernel build warning(s):
> arch/x86/hyperv/hv_spinlock.c:28:16: warning: variable ‘msr_val’ set but not used [-Wunused-but-set-variable]
>   unsigned long msr_val;
> 
> As Hypervisor Top-Level Functional Specification states in chapter 7.5 Virtual Processor Idle Sleep State, "A partition which possesses the AccessGuestIdleMsr privilege (refer to section 4.2.2) may trigger entry into the virtual processor idle sleep state through a read to the hypervisor-defined MSR HV_X64_MSR_GUEST_IDLE". That means only a read is necessary, msr_val is not uesed, so __maybe_unused should be added.
> 
> Reference:
> https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/reference/tlfs
> 
> Reported-by: Hulk Robot <hulkci@...wei.com>
> Signed-off-by: Xu Yihang <xuyihang@...wei.com>

I modified the commit message a bit and queued this up for hyperv-next.
Thanks.

Wei.