Re: [kvm-unit-tests PATCH v5 1/6] lib: s390x: introduce bitfield for PSW mask

Thomas Huth
2023-07-13T06:58:54Z

On 13/07/2023 08.56, Thomas Huth wrote:
> On 12/07/2023 13.41, Nico Boehr wrote:
>> Changing the PSW mask is currently little clumsy, since there is only the
>> PSW_MASK_* defines. This makes it hard to change e.g. only the address
>> space in the current PSW without a lot of bit fiddling.
>>
>> Introduce a bitfield for the PSW mask. This makes this kind of
>> modifications much simpler and easier to read.
>>
>> Signed-off-by: Nico Boehr <nrb@linux.ibm.com>
>> ---
>>   lib/s390x/asm/arch_def.h | 26 +++++++++++++++++++++++++-
>>   s390x/selftest.c         | 40 ++++++++++++++++++++++++++++++++++++++++
>>   2 files changed, 65 insertions(+), 1 deletion(-)
>>
>> diff --git a/lib/s390x/asm/arch_def.h b/lib/s390x/asm/arch_def.h
>> index bb26e008cc68..53279572a9ee 100644
>> --- a/lib/s390x/asm/arch_def.h
>> +++ b/lib/s390x/asm/arch_def.h
>> @@ -37,12 +37,36 @@ struct stack_frame_int {
>>   };
>>   struct psw {
>> -    uint64_t    mask;
>> +    union {
>> +        uint64_t    mask;
>> +        struct {
>> +            uint8_t reserved00:1;
>> +            uint8_t per:1;
>> +            uint8_t reserved02:3;
>> +            uint8_t dat:1;
>> +            uint8_t io:1;
>> +            uint8_t ext:1;
>> +            uint8_t key:4;
>> +            uint8_t reserved12:1;
>> +            uint8_t mchk:1;
>> +            uint8_t wait:1;
>> +            uint8_t pstate:1;
>> +            uint8_t as:2;
>> +            uint8_t cc:2;
>> +            uint8_t prg_mask:4;
>> +            uint8_t reserved24:7;
>> +            uint8_t ea:1;
>> +            uint8_t ba:1;
>> +            uint32_t reserved33:31;
>> +        };
>> +    };
>>       uint64_t    addr;
>>   };
>> +_Static_assert(sizeof(struct psw) == 16, "PSW size");
>>   #define PSW(m, a) ((struct psw){ .mask = (m), .addr = (uint64_t)(a) })
>> +
>>   struct short_psw {
>>       uint32_t    mask;
>>       uint32_t    addr;
>> diff --git a/s390x/selftest.c b/s390x/selftest.c
>> index 13fd36bc06f8..8d81ba312279 100644
>> --- a/s390x/selftest.c
>> +++ b/s390x/selftest.c
>> @@ -74,6 +74,45 @@ static void test_malloc(void)
>>       report_prefix_pop();
>>   }
>> +static void test_psw_mask(void)
>> +{
>> +    uint64_t expected_key = 0xF;
>> +    struct psw test_psw = PSW(0, 0);
>> +
>> +    report_prefix_push("PSW mask");
>> +    test_psw.dat = 1;
>> +    report(test_psw.mask == PSW_MASK_DAT, "DAT matches expected=0x%016lx
>> actual=0x%016lx", PSW_MASK_DAT, test_psw.mask);
>> +
>> +    test_psw.mask = 0;
>> +    test_psw.io = 1;
>> +    report(test_psw.mask == PSW_MASK_IO, "IO matches expected=0x%016lx
>> actual=0x%016lx", PSW_MASK_IO, test_psw.mask);
>> +
>> +    test_psw.mask = 0;
>> +    test_psw.ext = 1;
>> +    report(test_psw.mask == PSW_MASK_EXT, "EXT matches expected=0x%016lx
>> actual=0x%016lx", PSW_MASK_EXT, test_psw.mask);
>> +
>> +    test_psw.mask = expected_key << (63 - 11);
>> +    report(test_psw.key == expected_key, "PSW Key matches expected=0x%lx
>> actual=0x%x", expected_key, test_psw.key);
>
> Patch looks basically fine to me, but here my mind stumbled a little bit.
> This test is written the other way round than the others. Nothing wrong with
> that, it just feels a little bit inconsistent. I'd suggest to either do:
>
>     test_psw.mask = 0;
>     test_psw.key = expected_key;
>     report(test_psw.mask == expected_key << (63 - 11), ...);
>
> or maybe even switch all the other tests around instead, so you could get
> rid of the "test_psw.mask = 0" lines, e.g. :
>
>     test_psw.mask == PSW_MASK_IO;

s/==/=/ of course!

Sorry for that typo.

Thomas

>     report(test_psw.io, "IO matches ...");
>
> etc.
>
>  Thomas
>