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This patch adds a new configuration option, which adds support for a new
early_param which gets checked in arch/x86/kernel/setup_{32,64}.c:setup_arch()
to decide wether OHCI-1394 FireWire controllers should be initialized and
enabled for physical DMA access to allow remote debugging of early problems
like issues ACPI or other subsystems which are executed very early.
If the config option is not enabled, no code is changed, and if the boot
paramenter is not given, no new code is executed, and independent of that,
all new code is freed after boot, so the config option can be even enabled
in standard, non-debug kernels.
With specialized tools, it is then possible to get debugging information
from machines which have no serial ports (notebooks) such as the printk
buffer contents, or any data which can be referenced from global pointers,
if it is stored below the 4GB limit and even memory dumps of of the physical
RAM region below the 4GB limit can be taken without any cooperation from the
CPU of the host, so the machine can be crashed early, it does not matter.
In the extreme, even kernel debuggers can be accessed in this way. I wrote
a small kgdb module and an accompanying gdb stub for FireWire which allows
to gdb to talk to kgdb using remote remory reads and writes over FireWire.
An version of the gdb stub fore FireWire is able to read all global data
from a system which is running a a normal kernel without any kernel debugger,
without any interruption or support of the system's CPU. That way, e.g. the
task struct and so on can be read and even manipulated when the physical DMA
access is granted.
A HOWTO is included in this patch, in Documentation/debugging-via-ohci1394.txt
and I've put a copy online at
ftp://ftp.suse.de/private/bk/firewire/docs/debugging-via-ohci1394.txt
It also has links to all the tools which are available to make use of it
another copy of it is online at:
ftp://ftp.suse.de/private/bk/firewire/kernel/ohci1394_dma_early-v2.diff
Signed-Off-By: Bernhard Kaindl <bk@suse.de>
Tested-By: Thomas Renninger <trenn@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
99 lines
2.9 KiB
C
99 lines
2.9 KiB
C
/*
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* fixmap.h: compile-time virtual memory allocation
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*
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* This file is subject to the terms and conditions of the GNU General Public
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* License. See the file "COPYING" in the main directory of this archive
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* for more details.
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*
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* Copyright (C) 1998 Ingo Molnar
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*/
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#ifndef _ASM_FIXMAP_H
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#define _ASM_FIXMAP_H
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#include <linux/kernel.h>
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#include <asm/apicdef.h>
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#include <asm/page.h>
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#include <asm/vsyscall.h>
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#include <asm/efi.h>
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/*
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* Here we define all the compile-time 'special' virtual
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* addresses. The point is to have a constant address at
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* compile time, but to set the physical address only
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* in the boot process.
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*
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* These 'compile-time allocated' memory buffers are
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* fixed-size 4k pages (or larger if used with an increment
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* higher than 1). Use set_fixmap(idx,phys) to associate
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* physical memory with fixmap indices.
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*
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* TLB entries of such buffers will not be flushed across
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* task switches.
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*/
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enum fixed_addresses {
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VSYSCALL_LAST_PAGE,
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VSYSCALL_FIRST_PAGE = VSYSCALL_LAST_PAGE + ((VSYSCALL_END-VSYSCALL_START) >> PAGE_SHIFT) - 1,
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VSYSCALL_HPET,
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FIX_DBGP_BASE,
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FIX_EARLYCON_MEM_BASE,
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FIX_HPET_BASE,
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FIX_APIC_BASE, /* local (CPU) APIC) -- required for SMP or not */
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FIX_IO_APIC_BASE_0,
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FIX_IO_APIC_BASE_END = FIX_IO_APIC_BASE_0 + MAX_IO_APICS-1,
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FIX_EFI_IO_MAP_LAST_PAGE,
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FIX_EFI_IO_MAP_FIRST_PAGE = FIX_EFI_IO_MAP_LAST_PAGE+MAX_EFI_IO_PAGES-1,
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#ifdef CONFIG_PROVIDE_OHCI1394_DMA_INIT
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FIX_OHCI1394_BASE,
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#endif
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__end_of_fixed_addresses
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};
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extern void __set_fixmap (enum fixed_addresses idx,
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unsigned long phys, pgprot_t flags);
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#define set_fixmap(idx, phys) \
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__set_fixmap(idx, phys, PAGE_KERNEL)
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/*
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* Some hardware wants to get fixmapped without caching.
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*/
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#define set_fixmap_nocache(idx, phys) \
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__set_fixmap(idx, phys, PAGE_KERNEL_NOCACHE)
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#define FIXADDR_TOP (VSYSCALL_END-PAGE_SIZE)
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#define FIXADDR_SIZE (__end_of_fixed_addresses << PAGE_SHIFT)
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#define FIXADDR_START (FIXADDR_TOP - FIXADDR_SIZE)
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/* Only covers 32bit vsyscalls currently. Need another set for 64bit. */
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#define FIXADDR_USER_START ((unsigned long)VSYSCALL32_VSYSCALL)
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#define FIXADDR_USER_END (FIXADDR_USER_START + PAGE_SIZE)
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#define __fix_to_virt(x) (FIXADDR_TOP - ((x) << PAGE_SHIFT))
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extern void __this_fixmap_does_not_exist(void);
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/*
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* 'index to address' translation. If anyone tries to use the idx
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* directly without translation, we catch the bug with a NULL-deference
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* kernel oops. Illegal ranges of incoming indices are caught too.
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*/
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static __always_inline unsigned long fix_to_virt(const unsigned int idx)
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{
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/*
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* this branch gets completely eliminated after inlining,
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* except when someone tries to use fixaddr indices in an
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* illegal way. (such as mixing up address types or using
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* out-of-range indices).
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*
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* If it doesn't get removed, the linker will complain
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* loudly with a reasonably clear error message..
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*/
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if (idx >= __end_of_fixed_addresses)
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__this_fixmap_does_not_exist();
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return __fix_to_virt(idx);
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}
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#endif
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