xtensa: implement robust futex atomic uaccess ops

This enables the set_robust_list(2) system call.
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Chris Zankel <chris@zankel.net>

arch/xtensa/include/asm/Kbuild

@@ -8,7 +8,6 @@ generic-y += emergency-restart.h
 generic-y += errno.h
 generic-y += exec.h
 generic-y += fcntl.h
-generic-y += futex.h
 generic-y += hardirq.h
 generic-y += ioctl.h
 generic-y += irq_regs.h

arch/xtensa/include/asm/futex.h

+/*
+ * Atomic futex routines
+ *
+ * Based on the PowerPC implementataion
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * Copyright (C) 2013 TangoTec Ltd.
+ *
+ * Baruch Siach <baruch@tkos.co.il>
+ */
+
+#ifndef _ASM_XTENSA_FUTEX_H
+#define _ASM_XTENSA_FUTEX_H
+
+#ifdef __KERNEL__
+
+#include <linux/futex.h>
+#include <linux/uaccess.h>
+#include <linux/errno.h>
+
+#define __futex_atomic_op(insn, ret, oldval, uaddr, oparg) \
+	__asm__ __volatile(				\
+	"1:	l32i	%0, %2, 0\n"			\
+		insn "\n"				\
+	"	wsr	%0, scompare1\n"		\
+	"2:	s32c1i	%1, %2, 0\n"			\
+	"	bne	%1, %0, 1b\n"			\
+	"	movi	%1, 0\n"			\
+	"3:\n"						\
+	"	.section .fixup,\"ax\"\n"		\
+	"	.align 4\n"				\
+	"4:	.long	3b\n"				\
+	"5:	l32r	%0, 4b\n"			\
+	"	movi	%1, %3\n"			\
+	"	jx	%0\n"				\
+	"	.previous\n"				\
+	"	.section __ex_table,\"a\"\n"		\
+	"	.long 1b,5b,2b,5b\n"			\
+	"	.previous\n"				\
+	: "=&r" (oldval), "=&r" (ret)			\
+	: "r" (uaddr), "I" (-EFAULT), "r" (oparg)	\
+	: "memory")
+
+static inline int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
+{
+	int op = (encoded_op >> 28) & 7;
+	int cmp = (encoded_op >> 24) & 15;
+	int oparg = (encoded_op << 8) >> 20;
+	int cmparg = (encoded_op << 20) >> 20;
+	int oldval = 0, ret;
+	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
+		oparg = 1 << oparg;
+
+	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
+		return -EFAULT;
+
+#if !XCHAL_HAVE_S32C1I
+	return -ENOSYS;
+#endif
+
+	pagefault_disable();
+
+	switch (op) {
+	case FUTEX_OP_SET:
+		__futex_atomic_op("mov %1, %4", ret, oldval, uaddr, oparg);
+		break;
+	case FUTEX_OP_ADD:
+		__futex_atomic_op("add %1, %0, %4", ret, oldval, uaddr,
+				oparg);
+		break;
+	case FUTEX_OP_OR:
+		__futex_atomic_op("or %1, %0, %4", ret, oldval, uaddr,
+				oparg);
+		break;
+	case FUTEX_OP_ANDN:
+		__futex_atomic_op("and %1, %0, %4", ret, oldval, uaddr,
+				~oparg);
+		break;
+	case FUTEX_OP_XOR:
+		__futex_atomic_op("xor %1, %0, %4", ret, oldval, uaddr,
+				oparg);
+		break;
+	default:
+		ret = -ENOSYS;
+	}
+
+	pagefault_enable();
+
+	if (ret)
+		return ret;
+
+	switch (cmp) {
+	case FUTEX_OP_CMP_EQ: return (oldval == cmparg);
+	case FUTEX_OP_CMP_NE: return (oldval != cmparg);
+	case FUTEX_OP_CMP_LT: return (oldval < cmparg);
+	case FUTEX_OP_CMP_GE: return (oldval >= cmparg);
+	case FUTEX_OP_CMP_LE: return (oldval <= cmparg);
+	case FUTEX_OP_CMP_GT: return (oldval > cmparg);
+	}
+
+	return -ENOSYS;
+}
+
+static inline int
+futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
+			      u32 oldval, u32 newval)
+{
+	int ret = 0;
+	u32 prev;
+
+	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
+		return -EFAULT;
+
+#if !XCHAL_HAVE_S32C1I
+	return -ENOSYS;
+#endif
+
+	__asm__ __volatile__ (
+	"	# futex_atomic_cmpxchg_inatomic\n"
+	"1:	l32i	%1, %3, 0\n"
+	"	mov	%0, %5\n"
+	"	wsr	%1, scompare1\n"
+	"2:	s32c1i	%0, %3, 0\n"
+	"3:\n"
+	"	.section .fixup,\"ax\"\n"
+	"	.align 4\n"
+	"4:	.long	3b\n"
+	"5:	l32r	%1, 4b\n"
+	"	movi	%0, %6\n"
+	"	jx	%1\n"
+	"	.previous\n"
+	"	.section __ex_table,\"a\"\n"
+	"	.long 1b,5b,2b,5b\n"
+	"	.previous\n"
+	: "+r" (ret), "=&r" (prev), "+m" (*uaddr)
+	: "r" (uaddr), "r" (oldval), "r" (newval), "I" (-EFAULT)
+	: "memory");
+
+	*uval = prev;
+	return ret;
+}
+
+#endif /* __KERNEL__ */
+#endif /* _ASM_XTENSA_FUTEX_H */