[RFC][PATCH 4/12] x86: introduce copy_in_user() for 32-bit

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During the work of KVM's dirty page logging optimization, we encountered
the need of copy_in_user() for 32-bit x86 and ppc: these will be used for
manipulating dirty bitmaps in user space.

So we implement copy_in_user() for 32-bit with existing generic copy user

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@xxxxxxxxxxxxx>
Signed-off-by: Fernando Luis Vazquez Cao <fernando@xxxxxxxxxxxxx>
CC: Avi Kivity <avi@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CC: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
 arch/x86/include/asm/uaccess_32.h |    2 ++
 arch/x86/lib/usercopy_32.c        |   26 ++++++++++++++++++++++++++
 2 files changed, 28 insertions(+), 0 deletions(-)

diff --git a/arch/x86/include/asm/uaccess_32.h b/arch/x86/include/asm/uaccess_32.h
index 088d09f..85d396d 100644
--- a/arch/x86/include/asm/uaccess_32.h
+++ b/arch/x86/include/asm/uaccess_32.h
@@ -21,6 +21,8 @@ unsigned long __must_check __copy_from_user_ll_nocache
 		(void *to, const void __user *from, unsigned long n);
 unsigned long __must_check __copy_from_user_ll_nocache_nozero
 		(void *to, const void __user *from, unsigned long n);
+unsigned long __must_check copy_in_user
+		(void __user *to, const void __user *from, unsigned n);
  * __copy_to_user_inatomic: - Copy a block of data into user space, with less checking.
diff --git a/arch/x86/lib/usercopy_32.c b/arch/x86/lib/usercopy_32.c
index e218d5d..e90ffc3 100644
--- a/arch/x86/lib/usercopy_32.c
+++ b/arch/x86/lib/usercopy_32.c
@@ -889,3 +889,29 @@ void copy_from_user_overflow(void)
 	WARN(1, "Buffer overflow detected!\n");
+ * copy_in_user: - Copy a block of data from user space to user space.
+ * @to:   Destination address, in user space.
+ * @from: Source address, in user space.
+ * @n:    Number of bytes to copy.
+ *
+ * Context: User context only.  This function may sleep.
+ *
+ * Copy data from user space to user space.
+ *
+ * Returns number of bytes that could not be copied.
+ * On success, this will be zero.
+ */
+unsigned long
+copy_in_user(void __user *to, const void __user *from, unsigned n)
+	if (access_ok(VERIFY_WRITE, to, n) && access_ok(VERIFY_READ, from, n)) {
+		if (movsl_is_ok(to, from, n))
+			__copy_user(to, from, n);
+		else
+			n = __copy_user_intel(to, (const void *)from, n);
+	}
+	return n;

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