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

[Thomas Huth <thuth@redhat.com>]

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;
	report(test_psw.io, "IO matches ...");

etc.

  Thomas