[Qemu-devel] [PATCH v5 11/12] s390-ccw: clear pending irqs

["Collin L. Walling" <walling@linux.vnet.ibm.com>]

It is possible while waiting for multiple types of external
interrupts that we might have pending irqs remaining between
irq consumption and irq disabling. Those interrupts could
propagate to the guest after IPL completes and cause unwanted
behavior.

To avoid this, we clear the write event mask to prevent further
service interrupts from ASCII events and then consume all pending
irqs for a miniscule duration. Once finished, we reset the write
event mask and resume business as usual.

Signed-off-by: Collin L. Walling <walling@linux.vnet.ibm.com>
---
 pc-bios/s390-ccw/menu.c | 16 ++++++++++++++++
 pc-bios/s390-ccw/sclp.c | 12 ++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/pc-bios/s390-ccw/menu.c b/pc-bios/s390-ccw/menu.c
index 85d285f..971f6b6 100644
--- a/pc-bios/s390-ccw/menu.c
+++ b/pc-bios/s390-ccw/menu.c
@@ -64,6 +64,20 @@ static inline bool check_clock_int(void)
     return *code == 0x1004;
 }
 
+static void clear_pending_irqs(void)
+{
+    uint64_t time = 50 * TOD_CLOCK_SECOND / 0x3e8;
+
+    sclp_clear_write_mask();
+
+    set_clock_comparator(get_clock() + time);
+    enable_clock_int();
+    consume_sclp_int();
+    disable_clock_int();
+
+    sclp_setup(); /* re-enable write mask */
+}
+
 static int read_prompt(char *buf, size_t len)
 {
     char inp[2] = {};
@@ -165,6 +179,8 @@ static int get_boot_index(int entries)
     sclp_print("\nBooting entry #");
     sclp_print(itostr(boot_index, tmp, sizeof(tmp)));
 
+    clear_pending_irqs();
+
     return boot_index;
 }
 
diff --git a/pc-bios/s390-ccw/sclp.c b/pc-bios/s390-ccw/sclp.c
index 5902d5b..025eb2d 100644
--- a/pc-bios/s390-ccw/sclp.c
+++ b/pc-bios/s390-ccw/sclp.c
@@ -46,6 +46,18 @@ static int sclp_service_call(unsigned int command, void *sccb)
         return 0;
 }
 
+void sclp_clear_write_mask(void)
+{
+    WriteEventMask *sccb = (void *)_sccb;
+
+    sccb->h.length = sizeof(WriteEventMask);
+    sccb->mask_length = sizeof(unsigned int);
+    sccb->cp_receive_mask = 0;
+    sccb->cp_send_mask = 0;
+
+    sclp_service_call(SCLP_CMD_WRITE_EVENT_MASK, sccb);
+}
+
 static void sclp_set_write_mask(void)
 {
     WriteEventMask *sccb = (void *)_sccb;
-- 
2.7.4