[PATCH RFC 1/5] KVM: introduce a set_bit function for bitmaps in user space

Takuya Yoshikawa
2010-04-09T09:26:49Z

This work is initially suggested by Avi Kivity for moving the
dirty bitmaps used by KVM to user space: This makes it possible
to manipulate the bitmaps from qemu without copying from KVM.

Note: We are now brushing up this code before sending to x86's
maintainers.

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
---
arch/x86/include/asm/uaccess.h | 37 +++++++++++++++++++++++++++++++++++++
1 files changed, 37 insertions(+), 0 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index abd3e0e..25a694e 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -98,6 +98,43 @@ struct exception_table_entry {

extern int fixup_exception(struct pt_regs *regs);

+/**
+ * set_bit_user: - Set a bit of a bitmap in user space.
+ * @nr: Bit offset to set.
+ * @addr: Base address, in user space.
+ *
+ * Context: User context only. This function may sleep.
+ *
+ * This macro sets a bit of a bitmap in user space. Note that this
+ * is same as __set_bit but not set_bit in the sense that setting
+ * the bit is not done atomically.
+ *
+ * Returns zero on success, -EFAULT on error.
+ */
+#define __set_bit_user_asm(nr, addr, err, errret) \
+ asm volatile("1: bts %1,%2\n" \
+ "2:\n" \
+ ".section .fixup,\"ax\"\n" \
+ "3: mov %3,%0\n" \
+ " jmp 2b\n" \
+ ".previous\n" \
+ _ASM_EXTABLE(1b, 3b) \
+ : "=r"(err) \
+ : "r" (nr), "m" (__m(addr)), "i" (errret), "0" (err))
+
+#define set_bit_user(nr, addr) \
+({ \
+ int __ret_sbu = 0; \
+ \
+ might_fault(); \
+ if (access_ok(VERIFY_WRITE, addr, nr/8 + 1)) \
+ __set_bit_user_asm(nr, addr, __ret_sbu, -EFAULT); \
+ else \
+ __ret_sbu = -EFAULT; \
+ \
+ __ret_sbu; \
+})
+
/*
* These are the main single-value transfer routines. They automatically
* use the right size if we just have the right pointer type.
--
1.6.3.3