s390-ccw: set cp_receive mask only when needed and consume pending service irqs

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

As it is today, the SCLP will only recognize write events that
are enabled by the control program's send and receive masks. To
limit the window for, and prevent further irqs from, ASCII
console events (specifically keystrokes), we should only enable
the control program's receive mask when we need it.

While we're at it, remove assignment of the (non control program)
send and receive masks, as those are actually set by the SCLP.

Signed-off-by: Collin L. Walling <walling@linux.vnet.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

3 files changed, 10 insertions, 6 deletions

diff --git a/pc-bios/s390-ccw/menu.c b/pc-bios/s390-ccw/menu.c
index b99ff03298..8d55869448 100644
--- a/pc-bios/s390-ccw/menu.c
+++ b/pc-bios/s390-ccw/menu.c
@@ -11,6 +11,7 @@
 
 #include "libc.h"
 #include "s390-ccw.h"
+#include "sclp.h"
 
 #define KEYCODE_NO_INP '\0'
 #define KEYCODE_ESCAPE '\033'
@@ -116,8 +117,12 @@ static int get_index(void)
 
     memset(buf, 0, sizeof(buf));
 
+    sclp_set_write_mask(SCLP_EVENT_MASK_MSG_ASCII, SCLP_EVENT_MASK_MSG_ASCII);
+
     len = read_prompt(buf, sizeof(buf) - 1);
 
+    sclp_set_write_mask(0, SCLP_EVENT_MASK_MSG_ASCII);
+
     /* If no input, boot default */
     if (len == 0) {
         return 0;
diff --git a/pc-bios/s390-ccw/s390-ccw.h b/pc-bios/s390-ccw/s390-ccw.h
index aeba8b0a99..c4ddf9f228 100644
--- a/pc-bios/s390-ccw/s390-ccw.h
+++ b/pc-bios/s390-ccw/s390-ccw.h
@@ -69,6 +69,7 @@ unsigned int get_loadparm_index(void);
 
 /* sclp.c */
 void sclp_print(const char *string);
+void sclp_set_write_mask(uint32_t receive_mask, uint32_t send_mask);
 void sclp_setup(void);
 void sclp_get_loadparm_ascii(char *loadparm);
 int sclp_read(char *str, size_t count);
diff --git a/pc-bios/s390-ccw/sclp.c b/pc-bios/s390-ccw/sclp.c
index a2f25ebd4f..3836cb4716 100644
--- a/pc-bios/s390-ccw/sclp.c
+++ b/pc-bios/s390-ccw/sclp.c
@@ -46,23 +46,21 @@ static int sclp_service_call(unsigned int command, void *sccb)
         return 0;
 }
 
-static void sclp_set_write_mask(void)
+void sclp_set_write_mask(uint32_t receive_mask, uint32_t send_mask)
 {
     WriteEventMask *sccb = (void *)_sccb;
 
     sccb->h.length = sizeof(WriteEventMask);
     sccb->mask_length = sizeof(unsigned int);
-    sccb->receive_mask = SCLP_EVENT_MASK_MSG_ASCII;
-    sccb->cp_receive_mask = SCLP_EVENT_MASK_MSG_ASCII;
-    sccb->send_mask = SCLP_EVENT_MASK_MSG_ASCII;
-    sccb->cp_send_mask = SCLP_EVENT_MASK_MSG_ASCII;
+    sccb->cp_receive_mask = receive_mask;
+    sccb->cp_send_mask = send_mask;
 
     sclp_service_call(SCLP_CMD_WRITE_EVENT_MASK, sccb);
 }
 
 void sclp_setup(void)
 {
-    sclp_set_write_mask();
+    sclp_set_write_mask(0, SCLP_EVENT_MASK_MSG_ASCII);
 }
 
 long write(int fd, const void *str, size_t len)