Re: [kvm-unit-tests PATCH v3 1/6] lib: s390x: introduce bitfield for PSW mask

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

On 6/1/23 09:01, 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 | 25 ++++++++++++++++++++++++-
>   s390x/selftest.c         | 40 ++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 64 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/s390x/asm/arch_def.h b/lib/s390x/asm/arch_def.h
> index bb26e008cc68..84f6996c4d8c 100644
> --- a/lib/s390x/asm/arch_def.h
> +++ b/lib/s390x/asm/arch_def.h
> @@ -37,12 +37,35 @@ 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;

Hrm, since I already made the mistake of introducing bitfields with and 
without spaces between the ":" I'm in no position to complain here.

I'm also not sure what the consensus is.

> +		};
> +	};
>   	uint64_t	addr;
>   };

I've come to like static asserts for huge structs and bitfields since 
they can safe you from a *lot* of headaches.

>   
>   #define PSW(m, a) ((struct psw){ .mask = (m), .addr = (uint64_t)(a) })
>   
> +

Whitespace damage

>   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;

We're using lowercase chars for hex constants

> +	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);
> +
> +	test_psw.mask = 1UL << (63 - 13);
> +	report(test_psw.mchk, "MCHK matches");
> +
> +	test_psw.mask = 0;
> +	test_psw.wait = 1;
> +	report(test_psw.mask == PSW_MASK_WAIT, "Wait matches expected=0x%016lx actual=0x%016lx", PSW_MASK_WAIT, test_psw.mask);
> +
> +	test_psw.mask = 0;
> +	test_psw.pstate = 1;
> +	report(test_psw.mask == PSW_MASK_PSTATE, "Pstate matches expected=0x%016lx actual=0x%016lx", PSW_MASK_PSTATE, test_psw.mask);
> +
> +	test_psw.mask = 0;
> +	test_psw.ea = 1;
> +	test_psw.ba = 1;
> +	report(test_psw.mask == PSW_MASK_64, "BA/EA matches expected=0x%016lx actual=0x%016lx", PSW_MASK_64, test_psw.mask);
> +
> +	report_prefix_pop();
> +}
> +
>   int main(int argc, char**argv)
>   {
>   	report_prefix_push("selftest");
> @@ -89,6 +128,7 @@ int main(int argc, char**argv)
>   	test_fp();
>   	test_pgm_int();
>   	test_malloc();
> +	test_psw_mask();
>   
>   	return report_summary();
>   }