Virtualization - Nov 2022 - [PATCH 0/2] tools/virtio: remove smp_read_barrier_depends()

Hi,

To my surprise, this call is still git-greppable in the
tree, the kernel having gotten rid of it a while back.

Thanks!

Davidlohr Bueso (2):
  tools/virtio: remove stray characters
  tools/virtio: remove smp_read_barrier_depends()

 tools/virtio/ringtest/main.h | 37 +++++++++++++++++++-----------------
 1 file changed, 20 insertions(+), 17 deletions(-)

-- 
2.38.1

__read_once_size() is not a macro, remove those '/'s.

Signed-off-by: Davidlohr Bueso <dave at stgolabs.net>
---
 tools/virtio/ringtest/main.h | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/tools/virtio/ringtest/main.h b/tools/virtio/ringtest/main.h
index 6d1fccd3d86c..9ed09caa659e 100644
--- a/tools/virtio/ringtest/main.h
+++ b/tools/virtio/ringtest/main.h
@@ -149,16 +149,16 @@ static inline void busy_wait(void)
 static __always_inline
 void __read_once_size(const volatile void *p, void *res, int size)
 {
-        switch (size) {                                                 \
-        case 1: *(unsigned char *)res = *(volatile unsigned char *)p; break;   
\
-        case 2: *(unsigned short *)res = *(volatile unsigned short *)p; break; 
\
-        case 4: *(unsigned int *)res = *(volatile unsigned int *)p; break;     
\
-        case 8: *(unsigned long long *)res = *(volatile unsigned long long *)p;
break;            \
-        default:                                                        \
-                barrier();                                              \
-                __builtin_memcpy((void *)res, (const void *)p, size);   \
-                barrier();                                              \
-        }                                                               \
+	switch (size) {
+	case 1: *(unsigned char *)res = *(volatile unsigned char *)p; break;
+	case 2: *(unsigned short *)res = *(volatile unsigned short *)p; break;
+	case 4: *(unsigned int *)res = *(volatile unsigned int *)p; break;
+	case 8: *(unsigned long long *)res = *(volatile unsigned long long *)p; break;
+	default:
+		barrier();
+		__builtin_memcpy((void *)res, (const void *)p, size);
+		barrier();
+	}
 }
 
 static __always_inline void __write_once_size(volatile void *p, void *res, int
size)
-- 
2.38.1

This gets rid of the last references to smp_read_barrier_depends()
 which for the kernel side was removed in v5.9. The serialization
required for Alpha is done inside READ_ONCE() instead of having
users deal with it. Simply use a full barrier, the architecture
does not have rmb in the first place.

Signed-off-by: Davidlohr Bueso <dave at stgolabs.net>
---
 tools/virtio/ringtest/main.h | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/tools/virtio/ringtest/main.h b/tools/virtio/ringtest/main.h
index 9ed09caa659e..b68920d52750 100644
--- a/tools/virtio/ringtest/main.h
+++ b/tools/virtio/ringtest/main.h
@@ -140,12 +140,6 @@ static inline void busy_wait(void)
 #define smp_wmb() smp_release()
 #endif
 
-#ifdef __alpha__
-#define smp_read_barrier_depends() smp_acquire()
-#else
-#define smp_read_barrier_depends() do {} while(0)
-#endif
-
 static __always_inline
 void __read_once_size(const volatile void *p, void *res, int size)
 {
@@ -175,13 +169,22 @@ static __always_inline void __write_once_size(volatile
void *p, void *res, int s
 	}
 }
 
+#ifdef __alpha__
 #define READ_ONCE(x) \
 ({									\
 	union { typeof(x) __val; char __c[1]; } __u;			\
 	__read_once_size(&(x), __u.__c, sizeof(x));		\
-	smp_read_barrier_depends(); /* Enforce dependency ordering from x */ \
+	smp_mb(); /* Enforce dependency ordering from x */		\
 	__u.__val;							\
 })
+#else
+#define READ_ONCE(x)							\
+({									\
+	union { typeof(x) __val; char __c[1]; } __u;			\
+	__read_once_size(&(x), __u.__c, sizeof(x));			\
+	__u.__val;							\
+})
+#endif
 
 #define WRITE_ONCE(x, val) \
 ({							\
-- 
2.38.1