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SubjectRe: [PATCH v6 14/14] riscv: Make mmap allocation top-down by default
Date
On 10/8/19 10:07 PM, Atish Patra wrote:
> On Tue, 2019-10-08 at 07:58 -0400, Alex Ghiti wrote:
>> On 10/7/19 8:46 PM, Atish Patra wrote:
>>> On Mon, 2019-10-07 at 05:11 -0400, 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 6legacy_va_layout4BIT
>>>>>> + 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.
>>> Randomization may not be the issue. I just removed
>>> ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT from the config and that
>>> seems to
>>> work. Here is the bottom-up layout with randomization on.
>> Oups, sorry for my previous answer, I missed yours that landed in
>> another folder.
>>
>> Removing ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT also removes
>> randomization
>> as this config selects ARCH_HAS_ELF_RANDOMIZE.
>> You could remove ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT and selects by
>> hand
>> ARCH_HAS_ELF_RANDOMIZE but you would have to implement arch_mmap_rnd
>> and
>> arch_randomize_brk (elf-randomize.h).
>>
> Ahh okay.
>
>> The simplest would be to boot in legacy layout: I did not find a way
>> to
>> set this in kernel
>> command line, but you can by modifying it directly in the code:
>>
>> https://elixir.bootlin.com/linux/v5.4-rc2/source/kernel/sysctl.c#L269
>>
> Setting this to 1 works.
>
>>> [root@fedora-riscv ~]# cat /proc/self/maps
>>> 1555556000-1555570000 r-xp 00000000 103:01
>>> 280098 /usr/lib64/ld-2.28.so
>>> 1555570000-1555571000 r--p 00019000 103:01
>>> 280098 /usr/lib64/ld-2.28.so
>>> 1555571000-1555572000 rw-p 0001a000 103:01
>>> 280098 /usr/lib64/ld-2.28.so
>>> 1555572000-1555573000 rw-p 00000000 00:00 0
>>> 1555573000-1555575000 r-xp 00000000 00:00
>>> 0 [vdso]
>>> 1555575000-1555576000 r--p 00000000 103:01
>>> 50936 /usr/lib/locale/en_US.utf8/LC_IDENTIF
>>> ICAT
>>> ION
>>> 1555576000-155557d000 r--s 00000000 103:01
>>> 280826 /usr/lib64/gconv/gconv-modules.cache
>>> 155557d000-155557e000 r--p 00000000 103:01
>>> 50937 /usr/lib/locale/en_US.utf8/LC_MEASURE
>>> MENT
>>> 155557e000-155557f000 r--p 00000000 103:01
>>> 50939 /usr/lib/locale/en_US.utf8/LC_TELEPHO
>>> NE
>>> 155557f000-1555580000 r--p 00000000 103:01
>>> 3706 /usr/lib/locale/en_US.utf8/LC_ADDRESS
>>> 1555580000-1555581000 r--p 00000000 103:01
>>> 50944 /usr/lib/locale/en_US.utf8/LC_NAME
>>> 1555581000-1555582000 r--p 00000000 103:01
>>> 3775 /usr/lib/locale/en_US.utf8/LC_PAPER
>>> 1555582000-1555583000 r--p 00000000 103:01
>>> 3758 /usr/lib/locale/en_US.utf8/LC_MESSAGE
>>> S/SY
>>> S_LC_MESSAGES
>>> 1555583000-1555584000 r--p 00000000 103:01
>>> 50938 /usr/lib/locale/en_US.utf8/LC_MONETAR
>>> Y
>>> 1555584000-1555585000 r--p 00000000 103:01
>>> 50940 /usr/lib/locale/en_US.utf8/LC_TIME
>>> 1555585000-1555586000 r--p 00000000 103:01
>>> 50945 /usr/lib/locale/en_US.utf8/LC_NUMERIC
>>> 1555590000-1555592000 rw-p 00000000 00:00 0
>>> 1555592000-15556b1000 r-xp 00000000 103:01
>>> 280105 /usr/lib64/libc-2.28.so
>>> 15556b1000-15556b5000 r--p 0011e000 103:01
>>> 280105 /usr/lib64/libc-2.28.so
>>> 15556b5000-15556b7000 rw-p 00122000 103:01
>>> 280105 /usr/lib64/libc-2.28.so
>>> 15556b7000-15556bb000 rw-p 00000000 00:00 0
>>> 15556bb000-1555933000 r--p 00000000 103:01
>>> 3755 /usr/lib/locale/en_US.utf8/LC_COLLATE
>>> 1555933000-1555986000 r--p 00000000 103:01
>>> 50942 /usr/lib/locale/en_US.utf8/LC_CTYPE
>>> 1555986000-15559a8000 rw-p 00000000 00:00 0
>>> 2aaaaaa000-2aaaab1000 r-xp 00000000 103:01
>>> 283975 /usr/bin/cat
>>> 2aaaab1000-2aaaab2000 r--p 00006000 103:01
>>> 283975 /usr/bin/cat
>>> 2aaaab2000-2aaaab3000 rw-p 00007000 103:01
>>> 283975 /usr/bin/cat
>>> 2aaaab3000-2aaaad4000 rw-p 00000000 00:00
>>> 0 [heap]
>>> 3fffc97000-3fffcb8000 rw-p 00000000 00:00
>>> 0 [stack]
>>>
>>>
>>>> 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
>>>> :)
>>>>
>>> It stucks while booting. So I am not sure how to figure out which
>>> program stalls. It is difficult to figure out from boot log as it
>>> stucks at different places but soon after systemd starts.
>> If you can attach the running kernel, I would use vmlinux-gdb.py
>> commands
>> to figure out which processes are running (lx-ps command in
>> particular could
>> give us a hint). You can also add traces directly in the kernel and
>> either use
>> lx-dmesg command to print them from gdb or use your standard serial
>> output:
>> I would then print task_struct->comm at context switch to see which
>> process
>> is stuck.
>> To use the python script, you need to recompile with DEBUG_INFO and
>> GDB_SCRIPTS enabled.
>>
>> FYI, I have just booted a custom buildroot image based on kernel 5.4-
>> rc2.
>>
> vmlinux-gdb.py works only if you are running in Qemu or have a JTAG.
> Right ?

Yes. Does the problem appear on qemu too ?

> I am seeing this issue only on HiFive Unleashed + Microsemi Expansion
> board with Fedora Gnome desktop image. I can even boot a Fedora
> developer image on same hardware and a busybox image in Unleashed
> without any issues. But the issue is not specific to fedora as we see
> the same issue in OpenEmbedded disk image as well (HiFive Unleashed +
> Microsemi Expansion board).
>
> May be it gets triggerd only if bigger userspace ?

The purpose of this patch is, on the contrary, to not lose address space by
setting an arbitrary starting point (TASK_UNMAPPED_BASE) for mmap.

Do you a link to an image that fails to boot and reproduce the problem
on Qemu ?

I don't have much idea here, the only thing I can think of is finding
the application
that makes the boot stall and understand what is wrong.

>
>> Let me know if I can do anything.
>>
>> Alex
>>
>>>> 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

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