Re: [kvm-unit-tests PATCH v6 3/8] s390x: sie: switch to home space mode before entering SIE

[Thomas Huth <thuth@redhat.com>]

On 04/09/2023 10.22, Nico Boehr wrote:
> This is to prepare for running guests without MSO/MSL, which is
> currently not possible.
> 
> We already have code in sie64a to setup a guest primary ASCE before
> entering SIE, so we can in theory switch to the page tables which
> translate gpa to hpa.
> 
> But the host is running in primary space mode already, so changing the
> primary ASCE before entering SIE will also affect the host's code and
> data.
> 
> To make this switch useful, the host should run in a different address
> space mode. Hence, set up and change to home address space mode before
> installing the guest ASCE.
> 
> The home space ASCE is just copied over from the primary space ASCE, so
> no functional change is intended, also for tests that want to use
> MSO/MSL. If a test intends to use a different primary space ASCE, it can
> now just set the guest.asce in the save_area.
> 
> Signed-off-by: Nico Boehr <nrb@linux.ibm.com>
> ---
>   lib/s390x/asm/arch_def.h |  1 +
>   lib/s390x/sie.c          | 26 ++++++++++++++++++++++++++
>   2 files changed, 27 insertions(+)
> 
> diff --git a/lib/s390x/asm/arch_def.h b/lib/s390x/asm/arch_def.h
> index 5638fd01fd85..90a178ca0351 100644
> --- a/lib/s390x/asm/arch_def.h
> +++ b/lib/s390x/asm/arch_def.h
> @@ -93,6 +93,7 @@ enum address_space {
>   };
>   
>   #define PSW_MASK_DAT			0x0400000000000000UL
> +#define PSW_MASK_HOME			0x0000C00000000000UL
>   #define PSW_MASK_IO			0x0200000000000000UL
>   #define PSW_MASK_EXT			0x0100000000000000UL
>   #define PSW_MASK_KEY			0x00F0000000000000UL
> diff --git a/lib/s390x/sie.c b/lib/s390x/sie.c
> index b44febdeaaac..7f4474555ff7 100644
> --- a/lib/s390x/sie.c
> +++ b/lib/s390x/sie.c
> @@ -52,6 +52,8 @@ void sie_handle_validity(struct vm *vm)
>   
>   void sie(struct vm *vm)
>   {
> +	uint64_t old_cr13;
> +
>   	if (vm->sblk->sdf == 2)
>   		memcpy(vm->sblk->pv_grregs, vm->save_area.guest.grs,
>   		       sizeof(vm->save_area.guest.grs));
> @@ -59,6 +61,24 @@ void sie(struct vm *vm)
>   	/* Reset icptcode so we don't trip over it below */
>   	vm->sblk->icptcode = 0;
>   
> +	/*
> +	 * Set up home address space to match primary space. Instead of running
> +	 * in home space all the time, we switch every time in sie() because:
> +	 * - tests that depend on running in primary space mode don't need to be
> +	 *   touched
> +	 * - it avoids regressions in tests
> +	 * - switching every time makes it easier to extend this in the future,
> +	 *   for example to allow tests to run in whatever space they want

If we want tests to be able in other modes in the future...

> +	 */
> +	old_cr13 = stctg(13);
> +	lctlg(13, stctg(1));
> +
> +	/* switch to home space so guest tables can be different from host */
> +	psw_mask_set_bits(PSW_MASK_HOME);
> +
> +	/* also handle all interruptions in home space while in SIE */
> +	irq_set_dat_mode(true, AS_HOME);
> +
>   	while (vm->sblk->icptcode == 0) {
>   		sie64a(vm->sblk, &vm->save_area);
>   		sie_handle_validity(vm);
> @@ -66,6 +86,12 @@ void sie(struct vm *vm)
>   	vm->save_area.guest.grs[14] = vm->sblk->gg14;
>   	vm->save_area.guest.grs[15] = vm->sblk->gg15;
>   
> +	irq_set_dat_mode(true, AS_PRIM);
> +	psw_mask_clear_bits(PSW_MASK_HOME);

... we should maybe restore the previous mode here instead of switching 
always to primary mode?

Anyway, could be done later, but you might want to update your comment.

Reviewed-by: Thomas Huth <thuth@redhat.com>