Re: [PATCH 5/5] s390/uaccess: add cmpxchg_user_key()

Heiko Carstens
2022-11-09T22:24:47Z

On Wed, Nov 09, 2022 at 04:46:29PM +0100, Janis Schoetterl-Glausch wrote:
> On Wed, 2022-11-02 at 15:19 +0100, Heiko Carstens wrote:
> > + case 1: {
> > + unsigned int prev, tmp, shift;
> > +
> > + shift = (3 ^ (address & 3)) << 3;
> > + address ^= address & 3;
> > + asm volatile(
> > + " spka 0(%[key])\n"
> > + " sacf 256\n"
> > + "0: l %[prev],%[address]\n"
> > + "1: nr %[prev],%[mask]\n"
> > + " lr %[tmp],%[prev]\n"
> > + " or %[prev],%[old]\n"
> > + " or %[tmp],%[new]\n"
> > + "2: cs %[prev],%[tmp],%[address]\n"
> > + "3: jnl 4f\n"
> > + " xr %[tmp],%[prev]\n"
> > + " nr %[tmp],%[mask]\n"
>
> Are you only entertaining cosmetic changes to cmpxchg.h?

I fail to parse what you are trying to say. Please elaborate.

> The loop condition being imprecise seems non-ideal.

What exactly is imprecise?

> > + [key] "a" (key),
>
> Why did you get rid of the << 4 shift?
> That's inconsistent with the other uaccess functions that take an access key.

That's not only inconsistent, but also a bug.
Thank you for pointing this out. Will be fixed.