Re: [PATCH v6 14/14] riscv: Make mmap allocation top-down by default

[Alex Ghiti <alex@ghiti.fr>]

On 10/7/19 5:11 AM, Alex Ghiti wrote:
> On 10/4/19 10:12 PM, Atish Patra wrote:
>> On Thu, 2019-08-08 at 02:17 -0400, Alexandre Ghiti wrote:
>>> 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]
>>>
>>> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
>>> Acked-by: Paul Walmsley <paul.walmsley@sifive.com>
>>> Reviewed-by: Christoph Hellwig <hch@lst.de>
>>> Reviewed-by: Kees Cook <keescook@chromium.org>
>>> Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
>>> ---
>>>   arch/riscv/Kconfig | 12 ++++++++++++
>>>   1 file changed, 12 insertions(+)
>>>
>>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>>> index 59a4727ecd6c..87dc5370becb 100644
>>> --- a/arch/riscv/Kconfig
>>> +++ b/arch/riscv/Kconfig
>>> @@ -54,6 +54,18 @@ config RISCV
>>>       select EDAC_SUPPORT
>>>       select ARCH_HAS_GIGANTIC_PAGE
>>>       select ARCH_WANT_HUGE_PMD_SHARE 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 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
>> With this patch, I am not able to boot a Fedora Linux(a Gnome desktop
>> image) on RISC-V hardware (Unleashed + Microsemi Expansion board). The
>> booting gets stuck right after systemd starts.
>>
>> https://paste.fedoraproject.org/paste/TOrUMqqKH-pGFX7CnfajDg
>>
>> Reverting just this patch allow to boot Fedora successfully on specific
>> RISC-V hardware. I have not root caused the issue but it looks like it
>> might have messed userpsace mapping.
>
> It might have messed userspace mapping but not enough to make 
> userspace completely broken
> as systemd does some things. I would try to boot in legacy layout: if 
> you can try to set sysctl legacy_va_layout
> at boottime, it will map userspace as it was before (bottom-up). If 
> that does not work, the problem could
> be the randomization that is activated by default now.
> Anyway, it's weird since userspace should not depend on how the 
> mapping is.
>
> If you can identify the program that stalls, that would be fantastic :)
>
> As the code is common to mips and arm now and I did not hear from 
> them, I imagine the problem comes
> from us.
>
> Alex

Atish, do you have any news regarding this problem ? If you have an 
image I can execute on qemu that
reproduces the issue, I can take a look.

Alex

>>
>