[kvm-unit-tests,RFC,v3,11/13] s390x: Add sclp busy indication locking

Commit Message

Janosch Frank Dec. 18, 2018, 9:26 a.m. UTC

With smp CPUs have to compete for sclp. Let's add some locking, so
they execute sclp calls in an orderly fashion.

Signed-off-by: Janosch Frank <[e-mail]>
---
 lib/s390x/sclp.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

Patch

diff --git a/lib/s390x/sclp.c b/lib/s390x/sclp.c
index eed51ef..6b147d1 100644
--- a/lib/s390x/sclp.c
+++ b/lib/s390x/sclp.c
@@ -15,6 +15,7 @@ 
 #include <asm/arch_def.h>
 #include <asm/interrupt.h>
 #include <asm/barrier.h>
+#include <asm/spinlock.h>
 #include "sclp.h"
 #include <alloc_phys.h>
 
@@ -26,6 +27,7 @@  static uint64_t ram_size;
 
 char _sccb[PAGE_SIZE] __attribute__((__aligned__(4096)));
 volatile bool sclp_busy;
+static struct spinlock sclp_lock;
 
 static void mem_init(phys_addr_t mem_end)
 {
@@ -48,7 +50,9 @@  static void sclp_setup_int(void)
 void sclp_handle_ext(void)
 {
 	ctl_clear_bit(0, 9);
+	spin_lock(&sclp_lock);
 	sclp_busy = false;
+	spin_unlock(&sclp_lock);
 }
 
 void sclp_wait_busy(void)
@@ -60,7 +64,19 @@  void sclp_wait_busy(void)
 
 void sclp_mark_busy(void)
 {
+	/*
+	 * With multiple CPUs we might need to wait for another CPU's
+	 * request before grabbing the busy indication.
+	 */
+retry_wait:
+	sclp_wait_busy();
+	spin_lock(&sclp_lock);
+	if (sclp_busy) {
+		spin_unlock(&sclp_lock);
+		goto retry_wait;
+	}
 	sclp_busy = true;
+	spin_unlock(&sclp_lock);
 }
 
 static void sclp_read_scp_info(ReadInfo *ri, int length)