linux-kernel - Re: [PATCH 15/19] x86, mpx: do 32-bit-only cmpxchg for 32-bit apps

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Date:	Mon, 18 May 2015 23:22:06 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Dave Hansen <dave@...1.net>
cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	dave.hansen@...ux.intel.com
Subject: Re: [PATCH 15/19] x86, mpx: do 32-bit-only cmpxchg for 32-bit apps

On Fri, 8 May 2015, Dave Hansen wrote:
> +static int mpx_cmpxchg_bd_entry(struct mm_struct *mm,
> +		unsigned long *actual_old_val_ptr, long __user *bd_entry_addr,
> +		unsigned long expected_old_val, unsigned long new_bd_entry)

I know that you tried to use descriptive argument names, but the
result is close to camel case argument lists :)

Also why is *bd_entry_addr a long? Shouldn't that be unsigned long?

static int mpx_cmpxchg_bd_entry(struct mm_struct *mm,
       	   			unsigned long __user *addr,
				unsigned long oldval, unsigned long newval,
				unsigned long *curval)

or something like that should be sufficient, methinks.

> +{
> +	int ret;
> +	/*
> +	 * user_atomic_cmpxchg_inatomic() actually uses sizeof()
> +	 * the pointer that we pass to it to figure out how much
> +	 * data to cmpxchg.  We have to be careful here not to
> +	 * pass a pointer to a 64-bit data type when we only want
> +	 * a 32-bit copy.
> +	 */
> +	if (is_64bit_mm(mm)) {
> +		ret = user_atomic_cmpxchg_inatomic(actual_old_val_ptr,
> +				bd_entry_addr, expected_old_val, new_bd_entry);
> +	} else {
> +		u32 uninitialized_var(actual_old_val_32);
> +		u32 expected_old_val_32 = expected_old_val;
> +		u32 new_bd_entry_32 = new_bd_entry;
> +		u32 __user *bd_entry_32 = (u32 __user *)bd_entry_addr;

Newline between variables and code please.

> +		ret = user_atomic_cmpxchg_inatomic(&actual_old_val_32,
> +				bd_entry_32, expected_old_val_32,
> +				new_bd_entry_32);
> +		if (!ret)
> +			*actual_old_val_ptr = actual_old_val_32;

You can update that unconditionally.

Thanks,

	tglx
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