Re: [PATCH v10 6/6] x86/split_lock: Enable split lock detection by kernel parameter

[Andy Lutomirski]

On Thu, Nov 21, 2019 at 9:43 AM David Laight <David.Laight@xxxxxxxxxx> wrote:
>
> From: Ingo Molnar
> > Sent: 21 November 2019 17:12
> > * Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> ...
> > > This feature MUST be default enabled, otherwise everything will
> > > be/remain broken and we'll end up in the situation where you can't use
> > > it even if you wanted to.
> >
> > Agreed.
>
> Before it can be enabled by default someone needs to go through the
> kernel and fix all the code that abuses the 'bit' functions by using them
> on int[] instead of long[].
>
> I've only seen one fix go through for one use case of one piece of code
> that repeatedly uses potentially misaligned int[] arrays for bitmasks.
>

Can we really not just change the lock asm to use 32-bit accesses for
set_bit(), etc?  Sure, it will fail if the bit index is greater than
2^32, but that seems nuts.

(Why the *hell* do the bitops use long anyway?  They're *bit masks*
for crying out loud.  As in, users generally want to operate on fixed
numbers of bits.)

--Andy