linux-kernel - [PATCH v4 14/14] riscv: Make mmap allocation top-down by default

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Message-Id: <20190526134746.9315-15-alex@ghiti.fr>
Date:   Sun, 26 May 2019 09:47:46 -0400
From:   Alexandre Ghiti <alex@...ti.fr>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Christoph Hellwig <hch@....de>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        Palmer Dabbelt <palmer@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mips@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        Alexandre Ghiti <alex@...ti.fr>
Subject: [PATCH v4 14/14] riscv: Make mmap allocation top-down by default

In order to avoid wasting user address space by using bottom-up mmap
allocation scheme, prefer top-down scheme when possible.

Before:
root@...uriscv64:~# cat /proc/self/maps
00010000-00016000 r-xp 00000000 fe:00 6389       /bin/cat.coreutils
00016000-00017000 r--p 00005000 fe:00 6389       /bin/cat.coreutils
00017000-00018000 rw-p 00006000 fe:00 6389       /bin/cat.coreutils
00018000-00039000 rw-p 00000000 00:00 0          [heap]
1555556000-155556d000 r-xp 00000000 fe:00 7193   /lib/ld-2.28.so
155556d000-155556e000 r--p 00016000 fe:00 7193   /lib/ld-2.28.so
155556e000-155556f000 rw-p 00017000 fe:00 7193   /lib/ld-2.28.so
155556f000-1555570000 rw-p 00000000 00:00 0
1555570000-1555572000 r-xp 00000000 00:00 0      [vdso]
1555574000-1555576000 rw-p 00000000 00:00 0
1555576000-1555674000 r-xp 00000000 fe:00 7187   /lib/libc-2.28.so
1555674000-1555678000 r--p 000fd000 fe:00 7187   /lib/libc-2.28.so
1555678000-155567a000 rw-p 00101000 fe:00 7187   /lib/libc-2.28.so
155567a000-15556a0000 rw-p 00000000 00:00 0
3fffb90000-3fffbb1000 rw-p 00000000 00:00 0      [stack]

After:
root@...uriscv64:~# cat /proc/self/maps
00010000-00016000 r-xp 00000000 fe:00 6389       /bin/cat.coreutils
00016000-00017000 r--p 00005000 fe:00 6389       /bin/cat.coreutils
00017000-00018000 rw-p 00006000 fe:00 6389       /bin/cat.coreutils
2de81000-2dea2000 rw-p 00000000 00:00 0          [heap]
3ff7eb6000-3ff7ed8000 rw-p 00000000 00:00 0
3ff7ed8000-3ff7fd6000 r-xp 00000000 fe:00 7187   /lib/libc-2.28.so
3ff7fd6000-3ff7fda000 r--p 000fd000 fe:00 7187   /lib/libc-2.28.so
3ff7fda000-3ff7fdc000 rw-p 00101000 fe:00 7187   /lib/libc-2.28.so
3ff7fdc000-3ff7fe2000 rw-p 00000000 00:00 0
3ff7fe4000-3ff7fe6000 r-xp 00000000 00:00 0      [vdso]
3ff7fe6000-3ff7ffd000 r-xp 00000000 fe:00 7193   /lib/ld-2.28.so
3ff7ffd000-3ff7ffe000 r--p 00016000 fe:00 7193   /lib/ld-2.28.so
3ff7ffe000-3ff7fff000 rw-p 00017000 fe:00 7193   /lib/ld-2.28.so
3ff7fff000-3ff8000000 rw-p 00000000 00:00 0
3fff888000-3fff8a9000 rw-p 00000000 00:00 0      [stack]

Signed-off-by: Alexandre Ghiti <alex@...ti.fr>
Reviewed-by: Christoph Hellwig <hch@....de>
Reviewed-by: Kees Cook <keescook@...omium.org>
---
 arch/riscv/Kconfig | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index ee32c66e1af3..8c067ebd3ae0 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -49,6 +49,17 @@ config RISCV
 	select ARCH_HAS_PTE_SPECIAL
 	select ARCH_HAS_MMIOWB
 	select HAVE_EBPF_JIT if 64BIT
+	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU
+	select HAVE_ARCH_MMAP_RND_BITS
+
+config ARCH_MMAP_RND_BITS_MIN
+	default 18
+
+# max bits determined by the following formula:
+#  VA_BITS - PAGE_SHIFT - 3
+config ARCH_MMAP_RND_BITS_MAX
+	default 33 if 64BIT # SV48 based
+	default 18
 
 config MMU
 	def_bool y
-- 
2.20.1