From: Alexandre Ghiti <alex@xxxxxxxx> Subject: 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@qemuriscv64:~# 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@qemuriscv64:~# 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] [alex@xxxxxxxx: v6] Link: http://lkml.kernel.org/r/20190808061756.19712-15-alex@xxxxxxxx Link: http://lkml.kernel.org/r/20190730055113.23635-15-alex@xxxxxxxx Signed-off-by: Alexandre Ghiti <alex@xxxxxxxx> Reviewed-by: Christoph Hellwig <hch@xxxxxx> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> Reviewed-by: Luis Chamberlain <mcgrof@xxxxxxxxxx> Acked-by: Paul Walmsley <paul.walmsley@xxxxxxxxxx> [arch/riscv] Cc: Albert Ou <aou@xxxxxxxxxxxxxxxxx> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx> Cc: James Hogan <jhogan@xxxxxxxxxx> Cc: Palmer Dabbelt <palmer@xxxxxxxxxx> Cc: Paul Burton <paul.burton@xxxxxxxx> Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx> Cc: Russell King <linux@xxxxxxxxxxxxxxx> Cc: Will Deacon <will.deacon@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- arch/riscv/Kconfig | 12 ++++++++++++ 1 file changed, 12 insertions(+) --- a/arch/riscv/Kconfig~riscv-make-mmap-allocation-top-down-by-default +++ a/arch/riscv/Kconfig @@ -59,6 +59,18 @@ config RISCV select ARCH_HAS_GIGANTIC_PAGE select ARCH_WANT_HUGE_PMD_SHARE if 64BIT select SPARSEMEM_STATIC if 32BIT + select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU + select HAVE_ARCH_MMAP_RND_BITS + +config ARCH_MMAP_RND_BITS_MIN + default 18 if 64BIT + default 8 + +# max bits determined by the following formula: +# VA_BITS - PAGE_SHIFT - 3 +config ARCH_MMAP_RND_BITS_MAX + default 24 if 64BIT # SV39 based + default 17 config MMU def_bool y _
