From: Paul Walmsley <paul.walmsley@sifive.com>
To: Alexandre Ghiti <alex@ghiti.fr>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Albert Ou <aou@eecs.berkeley.edu>,
Daniel Cashman <dcashman@google.com>,
Kees Cook <keescook@chromium.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Palmer Dabbelt <palmer@sifive.com>,
Will Deacon <will.deacon@arm.com>,
Russell King <linux@armlinux.org.uk>,
Ralf Baechle <ralf@linux-mips.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Paul Burton <paul.burton@mips.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
James Hogan <jhogan@kernel.org>,
linux-fsdevel@vger.kernel.org, linux-riscv@lists.infradead.org,
linux-mips@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
linux-arm-kernel@lists.infradead.org,
Luis Chamberlain <mcgrof@kernel.org>
Subject: Re: [PATCH REBASE v4 14/14] riscv: Make mmap allocation top-down by default
Date: Thu, 25 Jul 2019 17:20:50 -0700 (PDT) [thread overview]
Message-ID: <alpine.DEB.2.21.9999.1907251655310.32766@viisi.sifive.com> (raw)
In-Reply-To: <20190724055850.6232-15-alex@ghiti.fr>
Hi Alexandre,
I have a few questions about this patch. Sorry to be dense here ...
On Wed, 24 Jul 2019, 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>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> ---
> arch/riscv/Kconfig | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 59a4727ecd6c..6a63973873fd 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -54,6 +54,17 @@ 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
Could you help me understand the rationale behind this constant?
> +
> +# max bits determined by the following formula:
> +# VA_BITS - PAGE_SHIFT - 3
I realize that these lines are probably copied from arch/arm64/Kconfig.
But the rationale behind the "- 3" is not immediately obvious. This
apparently originates from commit 8f0d3aa9de57 ("arm64: mm: support
ARCH_MMAP_RND_BITS"). Can you provide any additional context here?
> +config ARCH_MMAP_RND_BITS_MAX
> + default 33 if 64BIT # SV48 based
The rationale here is clear for Sv48, per the above formula:
(48 - 12 - 3) = 33
> + default 18
However, here it is less clear to me. For Sv39, shouldn't this be
(39 - 12 - 3) = 24
? And what about Sv32?
- Paul
next prev parent reply other threads:[~2019-07-26 0:20 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-24 5:58 [PATCH REBASE v4 00/14] Provide generic top-down mmap layout functions Alexandre Ghiti
2019-07-24 5:58 ` [PATCH REBASE v4 01/14] mm, fs: Move randomize_stack_top from fs to mm Alexandre Ghiti
2019-07-24 5:58 ` [PATCH REBASE v4 02/14] arm64: Make use of is_compat_task instead of hardcoding this test Alexandre Ghiti
2019-07-24 5:58 ` [PATCH REBASE v4 03/14] arm64: Consider stack randomization for mmap base only when necessary Alexandre Ghiti
2019-07-24 5:58 ` [PATCH REBASE v4 04/14] arm64, mm: Move generic mmap layout functions to mm Alexandre Ghiti
2019-07-24 5:58 ` [PATCH REBASE v4 05/14] arm64, mm: Make randomization selected by generic topdown mmap layout Alexandre Ghiti
2019-07-24 17:11 ` Luis Chamberlain
2019-07-25 5:48 ` Alexandre Ghiti
2019-07-24 5:58 ` [PATCH REBASE v4 06/14] arm: Properly account for stack randomization and stack guard gap Alexandre Ghiti
2019-07-24 5:58 ` [PATCH REBASE v4 07/14] arm: Use STACK_TOP when computing mmap base address Alexandre Ghiti
2019-07-24 5:58 ` [PATCH REBASE v4 08/14] arm: Use generic mmap top-down layout and brk randomization Alexandre Ghiti
2019-07-24 5:58 ` [PATCH REBASE v4 09/14] mips: Properly account for stack randomization and stack guard gap Alexandre Ghiti
2019-07-24 5:58 ` [PATCH REBASE v4 10/14] mips: Use STACK_TOP when computing mmap base address Alexandre Ghiti
2019-07-24 5:58 ` [PATCH REBASE v4 11/14] mips: Adjust brk randomization offset to fit generic version Alexandre Ghiti
2019-07-25 6:22 ` Alexandre Ghiti
2019-07-25 20:00 ` Kees Cook
2019-07-26 0:55 ` Andrew Morton
2019-07-24 5:58 ` [PATCH REBASE v4 12/14] mips: Replace arch specific way to determine 32bit task with " Alexandre Ghiti
2019-07-24 17:16 ` Luis Chamberlain
2019-07-25 6:09 ` Alexandre Ghiti
2019-07-24 5:58 ` [PATCH REBASE v4 13/14] mips: Use generic mmap top-down layout and brk randomization Alexandre Ghiti
2019-07-24 5:58 ` [PATCH REBASE v4 14/14] riscv: Make mmap allocation top-down by default Alexandre Ghiti
2019-07-26 0:20 ` Paul Walmsley [this message]
2019-07-26 11:48 ` Alexandre Ghiti
2019-07-26 20:15 ` Paul Walmsley
2019-07-24 17:17 ` [PATCH REBASE v4 00/14] Provide generic top-down mmap layout functions Luis Chamberlain
2019-07-25 6:10 ` Alexandre Ghiti
2019-07-24 20:18 ` [EXTERNAL][PATCH " Paul Burton
2019-07-25 6:21 ` Alexandre Ghiti
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