[kvm-unit-tests PATCH v2 1/2] s390x: introduce leave_pstate to leave userspace

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

In most testcases, we enter problem state (userspace) just to test if a
privileged instruction causes a fault. In some cases, though, we need
to test if an instruction works properly in userspace. This means that
we do not expect a fault, and we need an orderly way to leave problem
state afterwards.

This patch introduces a simple system based on the SVC instruction.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
---
 lib/s390x/asm/arch_def.h |  7 +++++++
 lib/s390x/interrupt.c    | 12 ++++++++++--
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/lib/s390x/asm/arch_def.h b/lib/s390x/asm/arch_def.h
index 9c4e330a..4cf8eb11 100644
--- a/lib/s390x/asm/arch_def.h
+++ b/lib/s390x/asm/arch_def.h
@@ -173,6 +173,8 @@ struct cpuid {
 	uint64_t reserved : 15;
 };
 
+#define SVC_LEAVE_PSTATE 1
+
 static inline unsigned short stap(void)
 {
 	unsigned short cpu_address;
@@ -276,6 +278,11 @@ static inline void enter_pstate(void)
 	load_psw_mask(mask);
 }
 
+static inline void leave_pstate(void)
+{
+	asm volatile("	svc %0\n" : : "i" (SVC_LEAVE_PSTATE));
+}
+
 static inline int stsi(void *addr, int fc, int sel1, int sel2)
 {
 	register int r0 asm("0") = (fc << 28) | sel1;
diff --git a/lib/s390x/interrupt.c b/lib/s390x/interrupt.c
index 1ce36073..d0567845 100644
--- a/lib/s390x/interrupt.c
+++ b/lib/s390x/interrupt.c
@@ -188,6 +188,14 @@ int unregister_io_int_func(void (*f)(void))
 
 void handle_svc_int(void)
 {
-	report_abort("Unexpected supervisor call interrupt: on cpu %d at %#lx",
-		     stap(), lc->svc_old_psw.addr);
+	uint16_t code = lc->svc_int_code;
+
+	switch (code) {
+	case SVC_LEAVE_PSTATE:
+		lc->svc_old_psw.mask &= ~PSW_MASK_PSTATE;
+		break;
+	default:
+		report_abort("Unexpected supervisor call interrupt: code %#x on cpu %d at %#lx",
+			      code, stap(), lc->svc_old_psw.addr);
+	}
 }
-- 
2.26.2