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

Nico Boehr
2023-07-13T09:25:55Z

Quoting Thomas Huth (2023-07-13 08:56:41)
> 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.

I like the latter option, thanks.