[kvm-unit-tests PATCH v5 3/6] s390x: sie: switch to home space mode before entering SIE

[Nico Boehr <nrb@linux.ibm.com>]

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          | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/lib/s390x/asm/arch_def.h b/lib/s390x/asm/arch_def.h
index 53279572a9ee..65e1cf58c7e7 100644
--- a/lib/s390x/asm/arch_def.h
+++ b/lib/s390x/asm/arch_def.h
@@ -91,6 +91,7 @@ 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);
+
 	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));
-- 
2.40.1