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

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Message-ID: <208433f810b5b07b1e679d7eedb028697dff851b.camel@wdc.com>
Date:   Sat, 5 Oct 2019 02:12:24 +0000
From:   Atish Patra <Atish.Patra@....com>
To:     "alex@...ti.fr" <alex@...ti.fr>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
CC:     "keescook@...omium.org" <keescook@...omium.org>,
        "ralf@...ux-mips.org" <ralf@...ux-mips.org>,
        "palmer@...ive.com" <palmer@...ive.com>,
        "aou@...s.berkeley.edu" <aou@...s.berkeley.edu>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "paul.walmsley@...ive.com" <paul.walmsley@...ive.com>,
        "paul.burton@...s.com" <paul.burton@...s.com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "hch@....de" <hch@....de>,
        "will.deacon@....com" <will.deacon@....com>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "jhogan@...nel.org" <jhogan@...nel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "mcgrof@...nel.org" <mcgrof@...nel.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v6 14/14] riscv: Make mmap allocation top-down by default

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@...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>
> Acked-by: Paul Walmsley <paul.walmsley@...ive.com>
> Reviewed-by: Christoph Hellwig <hch@....de>
> Reviewed-by: Kees Cook <keescook@...omium.org>
> Reviewed-by: Luis Chamberlain <mcgrof@...nel.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.

-- 
Regards,
Atish