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

[Janosch Frank <frankja@linux.ibm.com>]

On 1/16/24 14:02, Nina Schoetterl-Glausch wrote:
> 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).


That is a wonderful solution to this problem.
I'll send out a new version in the next couple of days.