Date: Wed, 29 Mar 2017 07:47:26 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Kan Liang <kan.liang@intel.com>
cc: peterz@infradead.org, mingo@redhat.com, linux-kernel@vger.kernel.org,
        bp@alien8.de, acme@kernel.org, eranian@google.com, jolsa@kernel.org,
        ak@linux.intel.com
Subject: Re: [PATCH V4 1/2] x86/msr: expose msr_flip_bit function
In-Reply-To: <1490751920-44720-2-git-send-email-kan.liang@intel.com>
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References: <1490751920-44720-1-git-send-email-kan.liang@intel.com> <1490751920-44720-2-git-send-email-kan.liang@intel.com>
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On Tue, 28 Mar 2017, kan.liang@intel.com wrote:
> From: Kan Liang <Kan.liang@intel.com>
> 
> There is no exported kernel interfaces which can flip a MSR bit. It has
> to do read-modify-write operation on the MSR through rd/wrmsr*
> interfaces. But the method is not atomic.
> 
> There is already __flip_bit support. Just rename and expose it.

This function is not atomic either. Protection has to be provided by the
caller.

> -static inline int __flip_bit(u32 msr, u8 bit, bool set)
> +int msr_flip_bit(u32 msr, u8 bit, bool set)
>  {
>  	struct msr m, m1;
>  	int err = -EINVAL;
> @@ -85,6 +85,7 @@ static inline int __flip_bit(u32 msr, u8 bit, bool set)
>  
>  	return 1;
>  }
> +EXPORT_SYMBOL_GPL(msr_flip_bit);

That export is not required. The call site is always built in.

Thanks,

	tglx