RISC-V: Fix sys_riscv_flush_icache

This contains a pair of patches that together fix sys_riscv_flush_icache
on all systems:

* The first enables sys_riscv_flush_icache() for non-SMP systems.
* The second fixes a bug in our syscall header that caused
  sys_riscv_flush_icache to never get generated.

arch/riscv/include/asm/unistd.h

@@ -11,6 +11,11 @@
  *   GNU General Public License for more details.
  */
 
+/*
+ * There is explicitly no include guard here because this file is expected to
+ * be included multiple times.  See uapi/asm/syscalls.h for more info.
+ */
+
 #define __ARCH_WANT_SYS_CLONE
 #include <uapi/asm/unistd.h>
 #include <uapi/asm/syscalls.h>

arch/riscv/include/asm/vdso.h

@@ -38,8 +38,6 @@ struct vdso_data {
 	(void __user *)((unsigned long)(base) + __vdso_##name);			\
 })
 
-#ifdef CONFIG_SMP
 asmlinkage long sys_riscv_flush_icache(uintptr_t, uintptr_t, uintptr_t);
-#endif
 
 #endif /* _ASM_RISCV_VDSO_H */

arch/riscv/include/uapi/asm/syscalls.h

 /* SPDX-License-Identifier: GPL-2.0 */
 /*
- * Copyright (C) 2017 SiFive
+ * Copyright (C) 2017-2018 SiFive
  */
 
-#ifndef _ASM__UAPI__SYSCALLS_H
-#define _ASM__UAPI__SYSCALLS_H
+/*
+ * There is explicitly no include guard here because this file is expected to
+ * be included multiple times in order to define the syscall macros via
+ * __SYSCALL.
+ */
 
 /*
  * Allows the instruction cache to be flushed from userspace.  Despite RISC-V
@@ -20,7 +23,7 @@
  * caller.  We don't currently do anything with the address range, that's just
  * in there for forwards compatibility.
  */
+#ifndef __NR_riscv_flush_icache
 #define __NR_riscv_flush_icache (__NR_arch_specific_syscall + 15)
-__SYSCALL(__NR_riscv_flush_icache, sys_riscv_flush_icache)
-
 #endif
+__SYSCALL(__NR_riscv_flush_icache, sys_riscv_flush_icache)

arch/riscv/kernel/sys_riscv.c

@@ -48,7 +48,6 @@ SYSCALL_DEFINE6(mmap2, unsigned long, addr, unsigned long, len,
 }
 #endif /* !CONFIG_64BIT */
 
-#ifdef CONFIG_SMP
 /*
  * Allows the instruction cache to be flushed from userspace.  Despite RISC-V
  * having a direct 'fence.i' instruction available to userspace (which we
@@ -66,15 +65,24 @@ SYSCALL_DEFINE6(mmap2, unsigned long, addr, unsigned long, len,
 SYSCALL_DEFINE3(riscv_flush_icache, uintptr_t, start, uintptr_t, end,
 	uintptr_t, flags)
 {
+#ifdef CONFIG_SMP
 	struct mm_struct *mm = current->mm;
 	bool local = (flags & SYS_RISCV_FLUSH_ICACHE_LOCAL) != 0;
+#endif
 
 	/* Check the reserved flags. */
 	if (unlikely(flags & ~SYS_RISCV_FLUSH_ICACHE_ALL))
 		return -EINVAL;
 
+	/*
+	 * Without CONFIG_SMP flush_icache_mm is a just a flush_icache_all(),
+	 * which generates unused variable warnings all over this function.
+	 */
+#ifdef CONFIG_SMP
 	flush_icache_mm(mm, local);
+#else
+	flush_icache_all();
+#endif
 
 	return 0;
 }
-#endif