arm64, mm: move generic mmap layout functions to mm

arm64 handles top-down mmap layout in a way that can be easily reused by
other architectures, so make it available in mm.  It then introduces a new
config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT that can be set by other
architectures to benefit from those functions.  Note that this new config
depends on MMU being enabled, if selected without MMU support, a warning
will be thrown.

Link: http://lkml.kernel.org/r/20190730055113.23635-5-alex@ghiti.fr
Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
Suggested-by: Christoph Hellwig <hch@infradead.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: James Hogan <jhogan@kernel.org>
Cc: Palmer Dabbelt <palmer@sifive.com>
Cc: Paul Burton <paul.burton@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/arch/Kconfig b/arch/Kconfig
index 0fcf8ec1e098..dfce421b8e8a 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -706,6 +706,16 @@ config HAVE_ARCH_COMPAT_MMAP_BASES
 	  and vice-versa 32-bit applications to call 64-bit mmap().
 	  Required for applications doing different bitness syscalls.
 
+# This allows to use a set of generic functions to determine mmap base
+# address by giving priority to top-down scheme only if the process
+# is not in legacy mode (compat task, unlimited stack size or
+# sysctl_legacy_va_layout).
+# Architecture that selects this option can provide its own version of:
+# - STACK_RND_MASK
+config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
+	bool
+	depends on MMU
+
 config HAVE_COPY_THREAD_TLS
 	bool
 	help