From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Christoph Hellwig <hch@lst.de>,
Linus Torvalds <torvalds@linux-foundation.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Michael Ellerman <mpe@ellerman.id.au>,
x86@kernel.org
Cc: linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org,
linuxppc-dev@lists.ozlabs.org, Kees Cook <keescook@chromium.org>,
linux-kernel@vger.kernel.org
Subject: Re: remove the last set_fs() in common code, and remove it for x86 and powerpc v2
Date: Tue, 1 Sep 2020 19:13:00 +0200 [thread overview]
Message-ID: <a8bb0319-0928-4687-9e9c-777c5860dbdd@csgroup.eu> (raw)
In-Reply-To: <20200827150030.282762-1-hch@lst.de>
Hi Christoph,
Le 27/08/2020 à 17:00, Christoph Hellwig a écrit :
> Hi all,
>
> this series removes the last set_fs() used to force a kernel address
> space for the uaccess code in the kernel read/write/splice code, and then
> stops implementing the address space overrides entirely for x86 and
> powerpc.
>
> The file system part has been posted a few times, and the read/write side
> has been pretty much unchanced. For splice this series drops the
> conversion of the seq_file and sysctl code to the iter ops, and thus loses
> the splice support for them. The reasons for that is that it caused a lot
> of churn for not much use - splice for these small files really isn't much
> of a win, even if existing userspace uses it. All callers I found do the
> proper fallback, but if this turns out to be an issue the conversion can
> be resurrected.
>
> Besides x86 and powerpc I plan to eventually convert all other
> architectures, although this will be a slow process, starting with the
> easier ones once the infrastructure is merged. The process to convert
> architectures is roughtly:
>
> (1) ensure there is no set_fs(KERNEL_DS) left in arch specific code
> (2) implement __get_kernel_nofault and __put_kernel_nofault
> (3) remove the arch specific address limitation functionality
>
> Changes since v1:
> - drop the patch to remove the non-iter ops for /dev/zero and
> /dev/null as they caused a performance regression
> - don't enable user access in __get_kernel on powerpc
> - xfail the set_fs() based lkdtm tests
>
> Diffstat:
>
I'm still sceptic with the results I get.
With 5.9-rc2:
root@vgoippro:~# time dd if=/dev/zero of=/dev/null count=1M
1048576+0 records in
1048576+0 records out
536870912 bytes (512.0MB) copied, 5.585880 seconds, 91.7MB/s
real 0m 5.59s
user 0m 1.40s
sys 0m 4.19s
With your series:
root@vgoippro:/tmp# time dd if=/dev/zero of=/dev/null count=1M
1048576+0 records in
1048576+0 records out
536870912 bytes (512.0MB) copied, 7.780540 seconds, 65.8MB/s
real 0m 7.79s
user 0m 2.12s
sys 0m 5.66s
Top of perf report of a standard perf record:
With 5.9-rc2:
20.31% dd [kernel.kallsyms] [k] __arch_clear_user
8.37% dd [kernel.kallsyms] [k] transfer_to_syscall
7.37% dd [kernel.kallsyms] [k] __fsnotify_parent
6.95% dd [kernel.kallsyms] [k] iov_iter_zero
5.72% dd [kernel.kallsyms] [k] new_sync_read
4.87% dd [kernel.kallsyms] [k] vfs_write
4.47% dd [kernel.kallsyms] [k] vfs_read
3.07% dd [kernel.kallsyms] [k] ksys_write
2.77% dd [kernel.kallsyms] [k] ksys_read
2.65% dd [kernel.kallsyms] [k] __fget_light
2.37% dd [kernel.kallsyms] [k] __fdget_pos
2.35% dd [kernel.kallsyms] [k] memset
1.53% dd [kernel.kallsyms] [k] rw_verify_area
1.52% dd [kernel.kallsyms] [k] read_iter_zero
With your series:
19.60% dd [kernel.kallsyms] [k] __arch_clear_user
10.92% dd [kernel.kallsyms] [k] iov_iter_zero
9.50% dd [kernel.kallsyms] [k] vfs_write
8.97% dd [kernel.kallsyms] [k] __fsnotify_parent
5.46% dd [kernel.kallsyms] [k] transfer_to_syscall
5.42% dd [kernel.kallsyms] [k] vfs_read
3.58% dd [kernel.kallsyms] [k] ksys_read
2.84% dd [kernel.kallsyms] [k] read_iter_zero
2.24% dd [kernel.kallsyms] [k] ksys_write
1.80% dd [kernel.kallsyms] [k] __fget_light
1.34% dd [kernel.kallsyms] [k] __fdget_pos
0.91% dd [kernel.kallsyms] [k] memset
0.91% dd [kernel.kallsyms] [k] rw_verify_area
Christophe
next prev parent reply other threads:[~2020-09-01 17:14 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-27 15:00 remove the last set_fs() in common code, and remove it for x86 and powerpc v2 Christoph Hellwig
2020-08-27 15:00 ` [PATCH 01/10] fs: don't allow kernel reads and writes without iter ops Christoph Hellwig
2020-08-27 15:58 ` David Laight
2020-08-29 9:23 ` 'Christoph Hellwig'
[not found] ` <20200901064849.GI4299@shao2-debian>
2020-09-01 7:08 ` [fs] ef30fb3c60: kernel write not supported for file /sys/kernel/softlockup_panic Christoph Hellwig
2020-08-27 15:00 ` [PATCH 02/10] fs: don't allow splice read/write without explicit ops Christoph Hellwig
2020-08-27 15:00 ` [PATCH 03/10] uaccess: add infrastructure for kernel builds with set_fs() Christoph Hellwig
2020-08-27 15:00 ` [PATCH 04/10] test_bitmap: skip user bitmap tests for !CONFIG_SET_FS Christoph Hellwig
2020-08-27 15:00 ` [PATCH 05/10] lkdtm: disable set_fs-based " Christoph Hellwig
2020-08-27 18:06 ` Linus Torvalds
2020-08-29 9:24 ` Christoph Hellwig
2020-09-01 18:52 ` Kees Cook
2020-09-01 18:57 ` Kees Cook
2020-09-02 8:09 ` Christoph Hellwig
2020-08-27 15:00 ` [PATCH 06/10] x86: move PAGE_OFFSET, TASK_SIZE & friends to page_{32,64}_types.h Christoph Hellwig
2020-08-27 15:00 ` [PATCH 07/10] x86: make TASK_SIZE_MAX usable from assembly code Christoph Hellwig
2020-08-27 15:00 ` [PATCH 08/10] x86: remove address space overrides using set_fs() Christoph Hellwig
2020-08-27 18:15 ` Linus Torvalds
2020-08-29 9:25 ` Christoph Hellwig
2020-08-27 15:00 ` [PATCH 09/10] powerpc: use non-set_fs based maccess routines Christoph Hellwig
2020-08-27 15:00 ` [PATCH 10/10] powerpc: remove address space overrides using set_fs() Christoph Hellwig
2020-09-02 6:15 ` Christophe Leroy
2020-09-02 12:36 ` Christoph Hellwig
2020-09-02 13:13 ` David Laight
2020-09-02 13:24 ` Christophe Leroy
2020-09-02 13:51 ` David Laight
2020-09-02 14:12 ` Christophe Leroy
2020-09-02 15:02 ` David Laight
2020-09-02 15:17 ` Christophe Leroy
2020-09-02 18:02 ` Linus Torvalds
2020-09-03 7:11 ` Christoph Hellwig
2020-09-03 7:27 ` Christophe Leroy
2020-09-03 8:55 ` Christophe Leroy
2020-09-03 7:20 ` Christophe Leroy
2020-08-27 15:31 ` remove the last set_fs() in common code, and remove it for x86 and powerpc v2 Christoph Hellwig
2020-09-01 17:13 ` Christophe Leroy [this message]
2020-09-01 17:25 ` Al Viro
2020-09-01 17:42 ` Matthew Wilcox
2020-09-01 18:39 ` Christophe Leroy
2020-09-01 19:01 ` Christophe Leroy
2020-09-02 8:10 ` Christoph Hellwig
2020-10-27 9:29 ` [PATCH 02/10] fs: don't allow splice read/write without explicit ops David Howells
2020-10-27 9:51 ` David Howells
2020-10-27 9:54 ` Christoph Hellwig
2020-10-27 10:38 ` David Howells
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