Re: [kvm-unit-tests PATCH v1 1/4] s390x: sie: switch to home space mode before entering SIE

[Janosch Frank <frankja@linux.ibm.com>]

On 3/27/23 10:21, 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.
> 
[...]
> +	/* set up home address space to match primary space */
> +	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 */
> +	lowcore.pgm_new_psw.mask |= PSW_MASK_DAT_HOME;

> +	lowcore.ext_new_psw.mask |= PSW_MASK_DAT_HOME;
> +	lowcore.io_new_psw.mask |= PSW_MASK_DAT_HOME;
We didn't enable DAT in these two cases as far as I can see so this is 
superfluous or we should change the mmu code. Also it's missing the svc 
and machine check.

The whole bit manipulation thing looks a bit crude. It might make more 
sense to drop into real mode for a few instructions and have a dedicated 
storage location for an extended PSW mask and an interrupt ASCE as part 
of the interrupt call code instead.

Opinions?

> +	mb();
> +
>   	while (vm->sblk->icptcode == 0) {
>   		sie64a(vm->sblk, &vm->save_area);
>   		sie_handle_validity(vm);
> @@ -60,6 +75,17 @@ void sie(struct vm *vm)
>   	vm->save_area.guest.grs[14] = vm->sblk->gg14;
>   	vm->save_area.guest.grs[15] = vm->sblk->gg15;
>   
> +	lowcore.pgm_new_psw.mask &= ~PSW_MASK_HOME;
> +	lowcore.ext_new_psw.mask &= ~PSW_MASK_HOME;
> +	lowcore.io_new_psw.mask &= ~PSW_MASK_HOME;
> +	mb();
> +
> +	psw_mask_clear_bits(PSW_MASK_HOME);
> +
> +	/* restore the old CR 13 */
> +	lctlg(13, old_cr13);
> +
> +
>   	if (vm->sblk->sdf == 2)
>   		memcpy(vm->save_area.guest.grs, vm->sblk->pv_grregs,
>   		       sizeof(vm->save_area.guest.grs));
> diff --git a/lib/s390x/sie.h b/lib/s390x/sie.h
> index 147cb0f2a556..0b00fb709776 100644
> --- a/lib/s390x/sie.h
> +++ b/lib/s390x/sie.h
> @@ -284,5 +284,6 @@ void sie_handle_validity(struct vm *vm);
>   void sie_guest_sca_create(struct vm *vm);
>   void sie_guest_create(struct vm *vm, uint64_t guest_mem, uint64_t guest_mem_len);
>   void sie_guest_destroy(struct vm *vm);
> +bool sie_had_pgm_int(struct vm *vm);
>   
>   #endif /* _S390X_SIE_H_ */