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

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.