[kvm-unit-tests GIT PULL 21/26] 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.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Link: https://lore.kernel.org/r/20231106163738.1116942-4-nrb@linux.ibm.com
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 5beaf15..745a338 100644
--- a/lib/s390x/asm/arch_def.h
+++ b/lib/s390x/asm/arch_def.h
@@ -92,6 +92,7 @@ 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 97a093b..b8ee43e 100644
--- a/lib/s390x/sie.c
+++ b/lib/s390x/sie.c
@@ -54,6 +54,8 @@ 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));
@@ -61,6 +63,24 @@ 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
+	 */
+	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);
@@ -68,6 +88,12 @@ 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);
+
+	/* 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));
-- 
2.41.0