vdso: Introduce vdso/cache.h

The vDSO implementation can only include headers from the vdso/
namespace. To enable the usage of ____cacheline_aligned from
the vDSO, move it and its dependencies into a new header vdso/cache.h.
Keep compatibility by including vdso/cache.h from linux/cache.h.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250303-vdso-clock-v1-1-c1b5c69a166f@linutronix.de

Author: t-8ch

include/linux/cache.h

@@ -3,16 +3,13 @@
 #define __LINUX_CACHE_H
 
 #include <uapi/linux/kernel.h>
+#include <vdso/cache.h>
 #include <asm/cache.h>
 
 #ifndef L1_CACHE_ALIGN
 #define L1_CACHE_ALIGN(x) __ALIGN_KERNEL(x, L1_CACHE_BYTES)
 #endif
 
-#ifndef SMP_CACHE_BYTES
-#define SMP_CACHE_BYTES L1_CACHE_BYTES
-#endif
-
 /**
  * SMP_CACHE_ALIGN - align a value to the L2 cacheline size
  * @x: value to align
@@ -63,10 +60,6 @@
 #define __ro_after_init __section(".data..ro_after_init")
 #endif
 
-#ifndef ____cacheline_aligned
-#define ____cacheline_aligned __attribute__((__aligned__(SMP_CACHE_BYTES)))
-#endif
-
 #ifndef ____cacheline_aligned_in_smp
 #ifdef CONFIG_SMP
 #define ____cacheline_aligned_in_smp ____cacheline_aligned

include/vdso/cache.h

@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __VDSO_CACHE_H
+#define __VDSO_CACHE_H
+
+#include <asm/cache.h>
+
+#ifndef SMP_CACHE_BYTES
+#define SMP_CACHE_BYTES L1_CACHE_BYTES
+#endif
+
+#ifndef ____cacheline_aligned
+#define ____cacheline_aligned __attribute__((__aligned__(SMP_CACHE_BYTES)))
+#endif
+
+#endif	/* __VDSO_ALIGN_H */