linux-kernel - Re: [RFC PATCH 1/3] x86: Add another set of MSR accessor functions

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Message-ID: <5302371B.4090403@zytor.com>
Date:	Mon, 17 Feb 2014 08:21:47 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...en8.de>, X86 ML <x86@...nel.org>
CC:	LKML <linux-kernel@...r.kernel.org>, Borislav Petkov <bp@...e.de>
Subject: Re: [RFC PATCH 1/3] x86: Add another set of MSR accessor functions

Good patch series overall, but I do have some issues with this one:

On 02/09/2014 05:48 AM, Borislav Petkov wrote:
> + */
> +int msr_read(u32 msr, struct msr *m)
> +{
> +	int err;
> +	u64 val;
> +
> +	val = native_read_msr_safe(msr, &err);

I don't think we should use the native_ function here.

> +	if (err)
> +		pr_warn("%s: Error reading MSR 0x%08x\n", __func__, msr);
> +	else
> +		m->q = val;

I also don't think we should print a message if the MSR doesn't exist.
This will be a normal occurrence in a number of flows.

> +static int __flip_bit(u32 msr, u8 bit, bool set)
> +{
> +	struct msr m;
> +
> +	if (bit > 63)
> +		return -1;

Feels a bit excessive, but I'd suggest returning -EINVAL instead.

I would suggest explicitly making this an inline function.

> +	if (msr_read(msr, &m))
> +		return -1;

Return -EIO?

How about:

	m1 = m;
	if (set)
		m1.q |= BIT_64(bit);
	else
		m1.q &= ~BIT_64(bit);

	if (m1.q != m.q) {
		if (msr_write(...))
			...
	}

> +
> +/**
> + * Set @bit in a MSR @msr.
> + *
> + * Retval:
> + * < 0: An error was encountered.
> + * = 0: Bit was already set.
> + * > 0: Hardware accepted the MSR write.
> + */
> +int msr_set_bit(u32 msr, u8 bit)
> +{
> +	int err = __flip_bit(msr, bit, true);
> +	if (err < 0)
> +		pr_err("%s: Error setting bit %d in MSR 0x%08x.\n",
> +			__func__, bit, msr);
> +
> +	return err;
> +}

Again, I'm not sure if printing a message here makes sense.  In fact,
this is the second message you print for the same thing.

	-hpa

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