linux/arch
Jeff Dike 3d564047a5 uml: start fixing os_read_file and os_write_file
This patch starts the removal of a very old, very broken piece of code.  This
stems from the problem of passing a userspace buffer into read() or write() on
the host.  If that buffer had not yet been faulted in, read and write will
return -EFAULT.

To avoid this problem, the solution was to fault the buffer in before the
system call by touching the pages that hold the buffer by doing a copy-user of
a byte to each page.  This is obviously bogus, but it does usually work, in tt
mode, since the kernel and process are in the same address space and userspace
addresses can be accessed directly in the kernel.

In skas mode, where the kernel and process are in separate address spaces, it
is completely bogus because the userspace address, which is invalid in the
kernel, is passed into the system call instead of the corresponding physical
address, which would be valid.  Here, it appears that this code, on every host
read() or write(), tries to fault in a random process page.  This doesn't seem
to cause any correctness problems, but there is a performance impact.  This
patch, and the ones following, result in a 10-15% performance gain on a kernel
build.

This code can't be immediately tossed out because when it is, you can't log
in.  Apparently, there is some code in the console driver which depends on
this somehow.

However, we can start removing it by switching the code which does I/O using
kernel addresses to using plain read() and write().  This patch introduces
os_read_file_k and os_write_file_k for use with kernel buffers and converts
all call locations which use obvious kernel buffers to use them.  These
include I/O using buffers which are local variables which are on the stack or
kmalloc-ed.  Later patches will handle the less obvious cases, followed by a
mass conversion back to the original interface.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-07 12:13:03 -07:00
..
alpha srmcons: fix kmalloc(GFP_KERNEL) inside spinlock 2007-05-07 12:12:58 -07:00
arm get_unmapped_area handles MAP_FIXED on arm 2007-05-07 12:12:56 -07:00
arm26 ARM26: remove useless config option GENERIC_BUST_SPINLOCK. 2007-05-07 12:12:58 -07:00
avr32 AVR32: Remove useless config option "GENERIC_BUST_SPINLOCK". 2007-04-27 13:45:26 +02:00
blackfin blackfin architecture 2007-05-07 12:12:58 -07:00
cris CRIS: remove code related to pre-2.2 kernel 2007-05-07 12:13:00 -07:00
frv get_unmapped_area handles MAP_FIXED on frv 2007-05-07 12:12:56 -07:00
h8300 h8300: add zImage support 2007-05-07 12:12:58 -07:00
i386 get_unmapped_area handles MAP_FIXED on i386 2007-05-07 12:12:56 -07:00
ia64 get_unmapped_area handles MAP_FIXED on ia64 2007-05-07 12:12:56 -07:00
m32r [PATCH] x86: Allow percpu variables to be page-aligned 2007-05-02 19:27:12 +02:00
m68k SPIN_LOCK_UNLOCKED cleanup in arch/m68k 2007-05-07 12:12:59 -07:00
m68knommu PCI: Cleanup the includes of <linux/pci.h> 2007-05-02 19:02:35 -07:00
mips RM9000 serial driver 2007-05-07 12:12:50 -07:00
parisc get_unmapped_area handles MAP_FIXED on parisc 2007-05-07 12:12:56 -07:00
powerpc slab allocators: Remove SLAB_DEBUG_INITIAL flag 2007-05-07 12:12:57 -07:00
ppc Merge branch 'for-linus' of git://one.firstfloor.org/home/andi/git/linux-2.6 2007-05-05 14:55:20 -07:00
s390 Introduce CONFIG_HAS_DMA 2007-05-07 12:12:51 -07:00
sh [PATCH] x86: Allow percpu variables to be page-aligned 2007-05-02 19:27:12 +02:00
sh64 Merge branch 'for-linus' of git://one.firstfloor.org/home/andi/git/linux-2.6 2007-05-05 14:55:20 -07:00
sparc [PATCH] x86: Allow percpu variables to be page-aligned 2007-05-02 19:27:12 +02:00
sparc64 get_unmapped_area handles MAP_FIXED on sparc64 2007-05-07 12:12:56 -07:00
um uml: start fixing os_read_file and os_write_file 2007-05-07 12:13:03 -07:00
v850 kbuild: Replace remaining "depends" with "depends on" 2007-02-17 19:05:24 +01:00
x86_64 swsusp: do not use page flags 2007-05-07 12:12:59 -07:00
xtensa Merge branch 'for-linus' of git://one.firstfloor.org/home/andi/git/linux-2.6 2007-05-05 14:55:20 -07:00