Re: [kvm-unit-tests PATCH 0/5] s390x: Dirty cc before executing tested instructions

[Nina Schoetterl-Glausch <nsg@linux.ibm.com>]

On Mon, 2024-01-08 at 13:29 +0000, Janosch Frank wrote:
> A recent s390 KVM fixpatch [1] showed us that checking the cc is not
> enough when emulation code forgets to set the cc. There might just be
> the correct cc in the PSW which would make the cc check succeed.
> 
> This series intentionally dirties the cc for sigp, uvc, some io
> instructions and sclp to make cc setting errors more apparent. I had a
> cursory look through the tested instructions and those are the most
> prominent ones with defined cc values.
> 
> Since the issue appeared in PQAP my AP test series is now dependent on
> this series.
> 
> [1] https://lore.kernel.org/kvm/20231201181657.1614645-1-farman@linux.ibm.com/

Using SET PROGRAM MASK the way you're doing in this series will also set the
program mask to 0, right?

In case you have some non zero register %[reg] and you want to set CC to 1 you
could do:

or	%[reg],%[reg] /* set CC to 1 */

In general, if I understand TEST UNDER MASK right, you could do:

tmll	%[set_cc],3

to set the CC to the value in %[set_cc] (without any shifting).