Re: [kvm-unit-tests PATCH v2 1/6] s390x: add function to set DAT mode for all interrupts

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

On Tue, 16 May 2023 15:04:51 +0200
Nico Boehr <nrb@linux.ibm.com> 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     | 38 ++++++++++++++++++++++++++++++++++++++
>  lib/s390x/mmu.c           |  5 +++--
>  3 files changed, 45 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
> +void irq_set_dat_mode(bool dat, uint64_t as);
> +
>  /* Activate low-address protection */
>  static inline void low_prot_enable(void)
>  {
> diff --git a/lib/s390x/interrupt.c b/lib/s390x/interrupt.c
> index 3f993a363ae2..1180ec44d72f 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 +105,43 @@ 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
> + * to initalize CRs, the restart new PSW is never touched to avoid the chicken
> + * 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)
> +{
> +	struct psw* irq_psws[] = {
> +		OPAQUE_PTR(GEN_LC_EXT_NEW_PSW),
> +		OPAQUE_PTR(GEN_LC_SVC_NEW_PSW),
> +		OPAQUE_PTR(GEN_LC_PGM_NEW_PSW),
> +		OPAQUE_PTR(GEN_LC_MCCK_NEW_PSW),
> +		OPAQUE_PTR(GEN_LC_IO_NEW_PSW),
> +		NULL /* sentinel */
> +	};
> +
> +	assert(as == AS_PRIM || as == AS_ACCR || as == AS_SECN || as == AS_HOME);
> +
> +	for (struct psw *irq_psw = irq_psws[0]; irq_psw != NULL; irq_psw++) {

just call it psw, or cur_psw, it's a little confusing otherwise

add in arch_def.c:

#define PSW_MASK_AS 0x0000C00000000000UL

> +		if (!dat)
> +			irq_psw->mask &= ~PSW_MASK_DAT;

cur_psw->mask &= ~(PSW_MASK_DAT | PSW_MASK_AS);
if (dat)
	cur_psw->mask |=  PSW_MASK_DAT | BIT_ULL(63 - 16);


alternatively, you can redefine psw with a bitfield (as you mentioned
offline):

cur_psw->mask.dat = dat;
if (dat)
	cur_psw->mask.as = as;

> +		else
> +			irq_psw->mask |= PSW_MASK_DAT | as << (63 - 16);

otherwise here you're ORing stuff to other stuff, if you had 3 and you
OR 0 you get 3, but you actually want 0

> +	}
> +
> +	mb();

what's the purpose of this?

> +}
> +
>  static void fixup_pgm_int(struct stack_frame_int *stack)
>  {
>  	/* If we have an error on SIE we directly move to sie_exit */
> diff --git a/lib/s390x/mmu.c b/lib/s390x/mmu.c
> index b474d7021d3f..199bd3fbc9c8 100644
> --- a/lib/s390x/mmu.c
> +++ b/lib/s390x/mmu.c
> @@ -12,6 +12,7 @@
>  #include <asm/pgtable.h>
>  #include <asm/arch_def.h>
>  #include <asm/barrier.h>
> +#include <asm/interrupt.h>
>  #include <vmalloc.h>
>  #include "mmu.h"
>  
> @@ -41,8 +42,8 @@ static void mmu_enable(pgd_t *pgtable)
>  	/* enable dat (primary == 0 set as default) */
>  	enable_dat();
>  
> -	/* we can now also use DAT unconditionally in our PGM handler */
> -	lowcore.pgm_new_psw.mask |= PSW_MASK_DAT;
> +	/* we can now also use DAT in all interrupt handlers */
> +	irq_set_dat_mode(IRQ_DAT_ON, AS_PRIM);
>  }
>  
>  /*