Re: [kvm-unit-tests PATCH v3 3/6] s390x: sie: switch to home space mode before entering SIE

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

On 6/1/23 09:01, Nico Boehr wrote:
> This is to prepare for running guests without MSO/MSL, which is
> currently not possible.

This is a preparation patch for non-MSO/MSL guest support.

> 
> 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.

The important information that's missing here is that SIE always uses 
the prim space for guest to host translations.

> 
> 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.

And that's why this is an issue.

For the time being we'll copy the primary ASCE into the home space ASCE. 
No functional change is intended. But if a test intends to....

> 
> 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          | 18 ++++++++++++++++++
>   2 files changed, 19 insertions(+)
> 
> diff --git a/lib/s390x/asm/arch_def.h b/lib/s390x/asm/arch_def.h
> index 84f6996c4d8c..099289e7550e 100644
> --- a/lib/s390x/asm/arch_def.h
> +++ b/lib/s390x/asm/arch_def.h
> @@ -90,6 +90,7 @@ struct cpu {
>   #define AS_HOME				3
>   
>   #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 9241b4b4a512..ffa8ec91a423 100644
> --- a/lib/s390x/sie.c
> +++ b/lib/s390x/sie.c
> @@ -46,6 +46,8 @@ 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));
> @@ -53,6 +55,16 @@ 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 */
> +	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(IRQ_DAT_ON, AS_HOME);

I'm wondering why this needs to be two calls when you clearly want to 
have a convenience function that does a full space change.

We could introduce:

#define AS_REAL 4

static void mmu_set_addr_space(uint8_t space)
{
	if (space < 4)
		psw_mask_set_bits(space);
	irq_set_dat_mode(space);
}

The "addr" in the function name is optional in my opinion.
@Claudio: What's your opinion?

> +
>   	while (vm->sblk->icptcode == 0) {
>   		sie64a(vm->sblk, &vm->save_area);
>   		sie_handle_validity(vm);
> @@ -60,6 +72,12 @@ 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(IRQ_DAT_ON, AS_PRIM);
> +	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));