On Fri, Jul 17, 2020 at 03:36:12PM -0700, Dave Hansen wrote:

On 7/17/20 1:54 AM, Peter Zijlstra wrote:

quoted

This is unbelievable junk...

Ouch!

This is from the original user pkeys implementation.

The thing I fell over most was new in this patch; the naming of that
function. It doesn't 'get' anything, nor does it allocate anything, so
'new' is out the window too.

quoted

How about something like:

u32 update_pkey_reg(u32 pk_reg, int pkey, unsigned int flags)
{
	int pkey_shift = pkey * PKR_BITS_PER_PKEY;

	pk_reg &= ~(((1 << PKR_BITS_PER_PKEY) - 1) << pkey_shift);

	if (flags & PKEY_DISABLE_ACCESS)
		pk_reg |= PKR_AD_BIT << pkey_shift;
	if (flags & PKEY_DISABLE_WRITE)
		pk_reg |= PKR_WD_BIT << pkey_shift;

	return pk_reg;
}

Then we at least have a little clue wtf the thing does.. Yes I started
with a rename and then got annoyed at the implementation too.

That's fine, if some comments get added.

I'm not sure what you would want commented; the code is trivial.

It looks correct to me but
probably compiles down to pretty much the same thing as what was there.
 FWIW, I prefer the explicit masking off of two bit values to implicit
masking off with a mask generated from PKR_BITS_PER_PKEY.  It's
certainly more compact, but I usually don't fret over the lines of code.

This way you're sure there are no bits missed. Both the shift and mask
use the same value.