Re: [kvm-unit-tests PATCH v5 2/6] s390x: add function to set DAT mode for all interrupts

Nico Boehr
2023-07-13T15:32:36Z

Quoting Thomas Huth (2023-07-13 09:17:28)
> On 12/07/2023 13.41, Nico Boehr wrote:
> > When toggling DAT or switch address space modes, it is likely that
> > interrupts should be handled in the same DAT or address space mode.
> >
> > Add a function which toggles DAT and address space mode for all
> > interruptions, except restart interrupts.
> >
> > Signed-off-by: Nico Boehr <nrb@linux.ibm.com>
> > ---
> > lib/s390x/asm/interrupt.h | 4 ++++
> > lib/s390x/interrupt.c | 36 ++++++++++++++++++++++++++++++++++++
> > lib/s390x/mmu.c | 5 +++--
> > 3 files changed, 43 insertions(+), 2 deletions(-)
> >
> > diff --git a/lib/s390x/asm/interrupt.h b/lib/s390x/asm/interrupt.h
> > index 35c1145f0349..55759002dce2 100644
> > --- a/lib/s390x/asm/interrupt.h
> > +++ b/lib/s390x/asm/interrupt.h
> > @@ -83,6 +83,10 @@ void expect_ext_int(void);
> > uint16_t clear_pgm_int(void);
> > void check_pgm_int_code(uint16_t code);
> >
> > +#define IRQ_DAT_ON true
> > +#define IRQ_DAT_OFF false
>
> Just a matter of taste, but IMHO having defines like this for just using
> them as boolean parameter to one function is a little bit overkill already.
> I'd rather rename the "bool dat" below into "bool use_dat" and then use
> "true" and "false" directly as a parameter for that function instead.
> Anyway, just my 0.02 \u20ac.

The point of having these defines was to convey the meaning of the parameter to my reader.

When I read

irq_set_dat_mode(true, AS_HOME);

it's less clear to me that the first parameter toggles the DAT mode compared to this:

irq_set_dat_mode(IRQ_DAT_ON, AS_HOME);

That being said, here it's pretty clear from the function name what the first parameter is, so what's the preferred opinion?

[...]
> > diff --git a/lib/s390x/interrupt.c b/lib/s390x/interrupt.c
> > index 3f993a363ae2..9b1bc6ce819d 100644
> > --- a/lib/s390x/interrupt.c
> > +++ b/lib/s390x/interrupt.c
> > @@ -9,6 +9,7 @@
> > */
> > #include <libcflat.h>
> > #include <asm/barrier.h>
> > +#include <asm/mem.h>
> > #include <asm/asm-offsets.h>
> > #include <sclp.h>
> > #include <interrupt.h>
> > @@ -104,6 +105,41 @@ void register_ext_cleanup_func(void (*f)(struct stack_frame_int *))
> > THIS_CPU->ext_cleanup_func = f;
> > }
> >
> > +/**
> > + * irq_set_dat_mode - Set the DAT mode of all interrupt handlers, except for
> > + * restart.
> > + * This will update the DAT mode and address space mode of all interrupt new
> > + * PSWs.
> > + *
> > + * Since enabling DAT needs initalized CRs and the restart new PSW is often used
>
> s/initalized/initialized/

Argh, thanks.

*reprioritizes task to look for a spell checker*

>
> > + * to initalize CRs, the restart new PSW is never touched to avoid the chicken
>
> dito
>
> > + * and egg situation.
> > + *
> > + * @dat specifies whether to use DAT or not
> > + * @as specifies the address space mode to use - one of AS_PRIM, AS_ACCR,
> > + * AS_SECN or AS_HOME.
> > + */
> > +void irq_set_dat_mode(bool dat, uint64_t as)
>
> why uint64_t for "as" ? "int" should be enough?
>
> (alternatively, you could turn the AS_* defines into a properly named enum
> and use that type here instead)

Yes, let's just do that.