linux-kernel - Re: [PATCH 1/2] x86/msr: add on cpu read/modify/write function

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Date:	Sun, 20 Dec 2015 14:28:48 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
cc:	LKML <linux-kernel@...r.kernel.org>,
	Linux PM <linux-pm@...r.kernel.org>,
	Rafael Wysocki <rafael.j.wysocki@...el.com>,
	Peter Zijlstra <peterz@...radead.org>,
	X86 Kernel <x86@...nel.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH 1/2] x86/msr: add on cpu read/modify/write function

Jacob,

On Fri, 11 Dec 2015, Jacob Pan wrote:
> +static inline int rmwmsrl_safe_on_cpu(unsigned int cpu, u32 msr_no, u64 mask, u64 bits)
> +{
> +	int err;
> +	u64 val;
> +
> +	err = rdmsrl_safe(msr_no, &val);
> +	if (err)
> +		goto out;
> +
> +	val &= ~mask;
> +	val |= bits;
> +
> +	err = wrmsrl_safe(msr_no, val);
> +out:
> +	return err;
> +}

....

> +static void __rmwmsrl_safe(void *info)
> +{
> +	int err;
> +	struct msr_action *ma = info;
> +	u64 val;
> +
> +	err = rdmsrl_safe(ma->msr_no, &val);
> +	if (err)
> +		goto out;
> +
> +	val &= ~ma->mask;
> +	val |= ma->bits;
> +
> +	err = wrmsrl_safe(ma->msr_no, val);
> +
> +out:
> +	ma->err = err;

So this is a copy of the above !SMP inline. What's wrong with providing:

 int rmwmsrl_safe(msr_no, clear_mask, set_mask)

in x86/lib/msr.c and make the !SMP variant of rdmsrl_safe_on_cpu() and that
variant for the SMP case a simple wrapper around it?

static void remote_rmwmsrl_safe(void *info)
{
	struct msr_action *ma = info;

	return rmwmsrl_safe(ma->msr, ma->clear_mask, ma->set_mask);
}

No gotos, no pointless code duplication. Just simple.

Thanks,

	tglx
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