linux-kernel - [PATCH 1/8] maccess: add a generic __{get,put}_kernel

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Date:   Fri,  4 Sep 2020 18:52:09 +0200
From:   Christoph Hellwig <hch@....de>
To:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Arnd Bergmann <arnd@...db.de>,
        Alexander Viro <viro@...iv.linux.org.uk>
Cc:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org
Subject: [PATCH 1/8] maccess: add a generic __{get,put}_kernel_nofault for nommu

Nommu architectures do not have page tables and thus no page faults.
Implement the maccess helpers using get_unaligned and put_unaligned and
enable them unconditionally for !CONFIG_MMU.

Signed-off-by: Christoph Hellwig <hch@....de>
---
 include/asm-generic/uaccess.h | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/include/asm-generic/uaccess.h b/include/asm-generic/uaccess.h
index ba68ee4dabfaa7..cc3b2c8b68fab4 100644
--- a/include/asm-generic/uaccess.h
+++ b/include/asm-generic/uaccess.h
@@ -9,6 +9,26 @@
  */
 #include <linux/string.h>
 
+#ifndef CONFIG_MMU
+#include <asm/unaligned.h>
+
+#define __get_kernel_nofault(dst, src, type, err_label)			\
+do {									\
+	*((type *)dst) = get_unaligned((type *)(src));			\
+	if (0) /* make sure the label looks used to the compiler */	\
+		goto err_label;						\
+} while (0)
+
+#define __put_kernel_nofault(dst, src, type, err_label)			\
+do {									\
+	put_unaligned(*((type *)src), (type *)(dst));			\
+	if (0) /* make sure the label looks used to the compiler */	\
+		goto err_label;						\
+} while (0)
+
+#define HAVE_GET_KERNEL_NOFAULT 1
+#endif /* !CONFIG_MMU */
+
 #ifdef CONFIG_UACCESS_MEMCPY
 static inline __must_check unsigned long
 raw_copy_from_user(void *to, const void __user * from, unsigned long n)
-- 
2.28.0