[PATCH RFC 2/2] x86/fpu: change xsave_user() and xrestore_user() to use __user_insn()

[Oleg Nesterov <oleg@redhat.com>]

Change xsave_user() and xrestore_user() to avoid the (imho) horrible
and should-die xstate_fault helper, they both can use __user_insn().

This also removes the "memory" clobber but I think it was never needed.
xrestore_user() doesn't change the memory, it only changes the FPU regs.
xsave_user() does write to "*buf" but this memory is "__user", we must
never access it directly.

This patch adds '"=m" (*buf)' in both cases, but this is only because
currently __user_insn() needs the non-empty "output" arg.

Note: I think we can change all other xstate_fault users too, including
alternative_input's.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 arch/x86/include/asm/xsave.h |   19 +++++--------------
 1 files changed, 5 insertions(+), 14 deletions(-)

diff --git a/arch/x86/include/asm/xsave.h b/arch/x86/include/asm/xsave.h
index 5fa9770..441f171 100644
--- a/arch/x86/include/asm/xsave.h
+++ b/arch/x86/include/asm/xsave.h
@@ -229,12 +229,8 @@ static inline int xsave_user(struct xsave_struct __user *buf)
 	if (unlikely(err))
 		return -EFAULT;
 
-	__asm__ __volatile__(ASM_STAC "\n"
-			     "1:"XSAVE"\n"
-			     "2: " ASM_CLAC "\n"
-			     xstate_fault
-			     : "D" (buf), "a" (-1), "d" (-1), "0" (0)
-			     : "memory");
+	err = __user_insn(XSAVE, "=m" (*buf), /* unneeded */
+				"D" (buf), "a" (-1), "d" (-1));
 	return err;
 }
 
@@ -243,17 +239,12 @@ static inline int xsave_user(struct xsave_struct __user *buf)
  */
 static inline int xrestore_user(struct xsave_struct __user *buf, u64 mask)
 {
-	int err = 0;
-	struct xsave_struct *xstate = ((__force struct xsave_struct *)buf);
 	u32 lmask = mask;
 	u32 hmask = mask >> 32;
+	int err;
 
-	__asm__ __volatile__(ASM_STAC "\n"
-			     "1:"XRSTOR"\n"
-			     "2: " ASM_CLAC "\n"
-			     xstate_fault
-			     : "D" (xstate), "a" (lmask), "d" (hmask), "0" (0)
-			     : "memory");	/* memory required? */
+	err = __user_insn(XRSTOR, "=m" (*buf), /* unneeded */
+				"D" (buf), "a" (lmask), "d" (hmask));
 	return err;
 }
 
-- 
1.5.5.1