[PATCH v2 1/3] introduce memcpy_nocache()

[Brian Boylston <brian.boylston@hpe.com>]

Introduce memcpy_nocache() as a memcpy() that avoids the processor cache
if possible.  Without arch-specific support, this defaults to just
memcpy().  For now, include arch-specific support for x86.

Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: <x86@kernel.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Brian Boylston <brian.boylston@hpe.com>
Reviewed-by: Toshi Kani <toshi.kani@hpe.com>
Reported-by: Oliver Moreno <oliver.moreno@hpe.com>
---
 arch/x86/include/asm/string_32.h |  3 +++
 arch/x86/include/asm/string_64.h |  3 +++
 arch/x86/lib/misc.c              | 12 ++++++++++++
 include/linux/string.h           | 15 +++++++++++++++
 4 files changed, 33 insertions(+)

diff --git a/arch/x86/include/asm/string_32.h b/arch/x86/include/asm/string_32.h
index 3d3e835..64f80c0 100644
--- a/arch/x86/include/asm/string_32.h
+++ b/arch/x86/include/asm/string_32.h
@@ -196,6 +196,9 @@ static inline void *__memcpy3d(void *to, const void *from, size_t len)
 
 #endif
 
+#define __HAVE_ARCH_MEMCPY_NOCACHE
+extern void *memcpy_nocache(void *dest, const void *src, size_t count);
+
 #define __HAVE_ARCH_MEMMOVE
 void *memmove(void *dest, const void *src, size_t n);
 
diff --git a/arch/x86/include/asm/string_64.h b/arch/x86/include/asm/string_64.h
index 90dbbd9..a8fdd55 100644
--- a/arch/x86/include/asm/string_64.h
+++ b/arch/x86/include/asm/string_64.h
@@ -51,6 +51,9 @@ extern void *__memcpy(void *to, const void *from, size_t len);
 #define memcpy(dst, src, len) __inline_memcpy((dst), (src), (len))
 #endif
 
+#define __HAVE_ARCH_MEMCPY_NOCACHE
+extern void *memcpy_nocache(void *dest, const void *src, size_t count);
+
 #define __HAVE_ARCH_MEMSET
 void *memset(void *s, int c, size_t n);
 void *__memset(void *s, int c, size_t n);
diff --git a/arch/x86/lib/misc.c b/arch/x86/lib/misc.c
index 76b373a..c993ab3 100644
--- a/arch/x86/lib/misc.c
+++ b/arch/x86/lib/misc.c
@@ -1,3 +1,6 @@
+#include <linux/export.h>
+#include <linux/uaccess.h>
+
 /*
  * Count the digits of @val including a possible sign.
  *
@@ -19,3 +22,12 @@ int num_digits(int val)
 	}
 	return d;
 }
+
+#ifdef __HAVE_ARCH_MEMCPY_NOCACHE
+void *memcpy_nocache(void *dest, const void *src, size_t count)
+{
+	__copy_from_user_inatomic_nocache(dest, src, count);
+	return dest;
+}
+EXPORT_SYMBOL(memcpy_nocache);
+#endif
diff --git a/include/linux/string.h b/include/linux/string.h
index 26b6f6a..7f40c41 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -102,6 +102,21 @@ extern void * memset(void *,int,__kernel_size_t);
 #ifndef __HAVE_ARCH_MEMCPY
 extern void * memcpy(void *,const void *,__kernel_size_t);
 #endif
+
+#ifndef __HAVE_ARCH_MEMCPY_NOCACHE
+/**
+ * memcpy_nocache - Copy one area of memory to another, avoiding the
+ * processor cache if possible
+ * @dest: Where to copy to
+ * @src: Where to copy from
+ * @count: The size of the area.
+ */
+static inline void *memcpy_nocache(void *dest, const void *src, size_t count)
+{
+	return memcpy(dest, src, count);
+}
+#endif
+
 #ifndef __HAVE_ARCH_MEMMOVE
 extern void * memmove(void *,const void *,__kernel_size_t);
 #endif
-- 
2.8.3