Early initrd file overwrite and ACPI table override making use of it

Early initrd file overwrite and ACPI table override making use of it

[Thomas Renninger]

Hi Peter,
another attempt, this time making use of cpio encapsulation
of early files as discussed.
Would be great if this can get committed to the branch you created
and get queued for 3.6-rc1 mainline inclusion.

It is based on Linus' master branch on top of:
commit 8c84bf4166a4698296342841a549bbee03860ac0
Merge: bd0a521 5db9a4d
Author: Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sun Jul 8 09:09:27 2012 -0700

    Merge branch 'for-3.5-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

Thanks,

   Thomas

[PATCH 1/2] init: Introduce early initrd files through uncompressed cpio passing

[Thomas Renninger]

cpio parsing code comes from  H. Peter Anvin.
The CONFIG_EARLY_INITRD feature is architecture independent, but
for now only enabled/called for X86.
The problem is that initrd_start must be valid, but there is no
architecture independent reserve_initrd() call in init/main.c or
similiar.

Signed-off-by: Thomas Renninger <trenn@suse.de>
CC: hpa@zytor.com
---
 Documentation/initrd.txt |   22 ++++++++
 arch/x86/kernel/setup.c  |    2 +
 include/linux/initrd.h   |   12 ++++
 init/Makefile            |    1 +
 init/initrd_early.c      |  131 ++++++++++++++++++++++++++++++++++++++++++++++
 usr/Kconfig              |   12 ++++
 6 files changed, 180 insertions(+), 0 deletions(-)
 create mode 100644 init/initrd_early.c

diff --git a/Documentation/initrd.txt b/Documentation/initrd.txt
index 4e1839c..e515e83 100644
--- a/Documentation/initrd.txt
+++ b/Documentation/initrd.txt
@@ -93,6 +93,28 @@ mkdir /tmp/imagefile
 cd /tmp/imagefile
 gzip -cd /boot/imagefile.img | cpio -imd --quiet
 
+
+Multiple cpio images glued together
+-----------------------------------
+
+Several cpio images, compressed or uncompressed can be concatenated.
+There is especially one use-case for this: see kernel accessing
+initrd data early section below.
+
+
+Accessing initrd data early
+---------------------------
+
+There is a mechanism to access data passed from the initrd much earlier.
+This only works if the data needed early is encapsulated in an uncompressed
+cpio image is passed. It must be the first cpio archive if multiple
+cpio archives are concatenated and passed as initrd.
+Typically if you want to pass data which is supposed to be consumed by
+the kernel really early, one would pass two cpio images glued together:
+   - One compressed, holding the big data which is needed by userspace
+   - One uncompressed cpio image holding files for early kernel initialization
+For further details look out for the CONFIG_EARLY_INITRD option in the sources.
+
 Installation
 ------------
 
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 16be6dc..9e039f6 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -941,6 +941,8 @@ void __init setup_arch(char **cmdline_p)
 
 	reserve_initrd();
 
+	early_initrd_find_cpio_data((void *)initrd_start, initrd_end - initrd_start);
+
 	reserve_crashkernel();
 
 	vsmp_init();
diff --git a/include/linux/initrd.h b/include/linux/initrd.h
index 55289d2..3fe262e 100644
--- a/include/linux/initrd.h
+++ b/include/linux/initrd.h
@@ -18,3 +18,15 @@ extern unsigned long initrd_start, initrd_end;
 extern void free_initrd_mem(unsigned long, unsigned long);
 
 extern unsigned int real_root_dev;
+
+
+#define MAX_EARLY_INITRD_CB 16
+
+#ifdef CONFIG_EARLY_INITRD
+extern int early_initrd_find_cpio_data(const char *data, size_t len);
+#else
+static int early_initrd_find_cpio_data(const char *data, size_t len)
+{
+	return 0;
+}
+#endif
diff --git a/init/Makefile b/init/Makefile
index 7bc47ee..c8408ec 100644
--- a/init/Makefile
+++ b/init/Makefile
@@ -9,6 +9,7 @@ else
 obj-$(CONFIG_BLK_DEV_INITRD)   += initramfs.o
 endif
 obj-$(CONFIG_GENERIC_CALIBRATE_DELAY) += calibrate.o
+obj-$(CONFIG_EARLY_INITRD)     += initrd_early.o
 
 ifneq ($(CONFIG_ARCH_INIT_TASK),y)
 obj-y                          += init_task.o
diff --git a/init/initrd_early.c b/init/initrd_early.c
new file mode 100644
index 0000000..c657a4b
--- /dev/null
+++ b/init/initrd_early.c
@@ -0,0 +1,131 @@
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/initrd.h>
+
+struct initrd_early_data {
+	/* Path where relevant files can be found in uncompressed cpio */
+ 	char *namesp;
+	/* Callback called for each found file in above path */
+	int (*cb)(void *data, int size, const char *name);
+	/* Finalize callback: Called if file scanning finished and above
+	   callback has been called one or more times successfully */
+	void (*final)(void);
+};
+
+/*
+ * Add here new callback functions and the path relevant files show up in an
+ * uncompressed cpio
+ */
+static __initdata struct initrd_early_data initrd_early_callbacks[] =
+{
+	{
+		.namesp = NULL,
+	}
+};
+
+enum cpio_fields {
+	C_MAGIC,
+	C_INO,
+	C_MODE,
+	C_UID,
+	C_GID,
+	C_NLINK,
+	C_MTIME,
+	C_FILESIZE,
+	C_MAJ,
+	C_MIN,
+	C_RMAJ,
+	C_RMIN,
+	C_NAMESIZE,
+	C_CHKSUM,
+	C_NFIELDS
+};
+
+#define ALIGN4(p) ((void *)(((size_t)p + 3) & ~3))
+
+void __init early_initrd_find_cpio_data(const char *data, size_t len)
+{
+	const size_t cpio_header_len = 8*C_NFIELDS - 2;
+	const char *p, *dptr, *nptr;
+	unsigned int ch[C_NFIELDS], *chp, v;
+	unsigned char c, x;
+	int i, j;
+	struct initrd_early_data *ied;
+	int str_len[MAX_EARLY_INITRD_CB];
+	int match[MAX_EARLY_INITRD_CB];
+
+	for(i = 0, ied = initrd_early_callbacks; ied->namesp; ied++, i++) {
+		str_len[i] = strlen(ied->namesp);
+		match[i] = 0;
+	}
+
+	p = data;
+
+	while (len > cpio_header_len) {
+		if (!*p) {
+			/* All cpio headers need to be 4-byte aligned */
+			p += 4;
+			len -= 4;
+			continue;
+		}
+
+		j = 6;		/* The magic field is only 6 characters */
+		chp = ch;
+		for (i = C_NFIELDS; i; i--) {
+			v = 0;
+			while (j--) {
+				v <<= 4;
+				c = *p++;
+
+				x = c - '0';
+				if (x < 10) {
+					v += x;
+					continue;
+				}
+
+				x = (c | 0x20) - 'a';
+				if (x < 6) {
+					v += x + 10;
+					continue;
+				}
+
+				goto quit; /* Invalid hexadecimal */
+			}
+			*chp++ = v;
+			j = 8;	/* All other fields are 8 characters */
+		}
+
+		if ((ch[C_MAGIC] - 0x070701) > 1)
+			goto quit; /* Invalid magic */
+
+		len -= cpio_header_len;
+
+		dptr = ALIGN4(p + ch[C_NAMESIZE]);
+		nptr = ALIGN4(dptr + ch[C_FILESIZE]);
+
+		if (nptr > p + len || dptr < p || nptr < dptr)
+			goto quit; /* Buffer overrun */
+
+		if ((ch[C_MODE] & 0170000) == 0100000) {
+			for(i = 0, ied = initrd_early_callbacks; ied->namesp;
+			    ied++, i++) {
+				int min_len = (str_len[i] < ch[C_NAMESIZE])
+					? str_len[i] : ch[C_NAMESIZE];
+				if (!memcmp(p, ied->namesp, min_len)) {
+					if (!ied->cb((void *)dptr,
+					     ch[C_FILESIZE], p + min_len))
+						match[i]++;
+				}
+			}
+		}
+
+		len -= (nptr - p);
+		p = nptr;
+	}
+
+quit:
+	for(i = 0, ied = initrd_early_callbacks; ied->namesp; ied++, i++) {
+		if (match[i])
+			ied->final();
+	}
+}
diff --git a/usr/Kconfig b/usr/Kconfig
index 085872b..3b832ed 100644
--- a/usr/Kconfig
+++ b/usr/Kconfig
@@ -166,3 +166,15 @@ config INITRAMFS_COMPRESSION_LZO
 	  (both compression and decompression) is the fastest.
 
 endchoice
+
+config EARLY_INITRD
+	bool "Ability to pass data to the kernel which is needed really early"
+	default y
+	depends on BLK_DEV_INITRD && X86
+	help
+	 CPU microcode updates could be loaded before CPU initialization.
+	 BIOS data can be overridden via initrd for debugging purposes.
+	 If you are unsure whether your Hardware or kernel makes use of this,
+	 it is safe to say yes here. As long as no data is passed through an
+	 uncompressed cpio via initrd the kernel could make use of, nothing
+	 will happen.
-- 
1.7.6.1

Re: [PATCH 1/2] init: Introduce early initrd files through uncompressed cpio passing

[H. Peter Anvin]

On 07/18/2012 03:36 AM, Thomas Renninger wrote:
> cpio parsing code comes from  H. Peter Anvin.
> The CONFIG_EARLY_INITRD feature is architecture independent, but
> for now only enabled/called for X86.
> The problem is that initrd_start must be valid, but there is no
> architecture independent reserve_initrd() call in init/main.c or
> similiar.
> + * Add here new callback functions and the path relevant files show up in an
> + * uncompressed cpio
> + */
> +static __initdata struct initrd_early_data initrd_early_callbacks[] =
> +{
> +	{
> +		.namesp = NULL,
> +	}
> +};
> +

I don't like your callback interface at all.  In fact, it is actively 
broken, because it assumes that all early users are runnable at the same 
time, which is trivially shown false -- the microcode work that Fenghua 
Yu is working on needs access to its early data much, much earlier than 
your ACPI code.

So big NAK on this change.  Instead we should stick to the imperative 
interface that I had in my original code (call the search function with 
a filename and let it return a pointer if found.)

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

Re: [PATCH 1/2] init: Introduce early initrd files through uncompressed cpio passing

[H. Peter Anvin]

On 07/18/2012 03:36 AM, Thomas Renninger wrote:
> cpio parsing code comes from  H. Peter Anvin.
> The CONFIG_EARLY_INITRD feature is architecture independent, but
> for now only enabled/called for X86.
> The problem is that initrd_start must be valid, but there is no
> architecture independent reserve_initrd() call in init/main.c or
> similiar.
> + * Add here new callback functions and the path relevant files show up in an
> + * uncompressed cpio
> + */
> +static __initdata struct initrd_early_data initrd_early_callbacks[] =
> +{
> +	{
> +		.namesp = NULL,
> +	}
> +};
> +

I don't like your callback interface at all.  In fact, it is actively 
broken, because it assumes that all early users are runnable at the same 
time, which is trivially shown false -- the microcode work that Fenghua 
Yu is working on needs access to its early data much, much earlier than 
your ACPI code.

So big NAK on this change.  Instead we should stick to the imperative 
interface that I had in my original code (call the search function with 
a filename and let it return a pointer if found.)

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

Re: [PATCH 1/2] init: Introduce early initrd files through uncompressed cpio passing

[Thomas Renninger]

On Saturday, July 21, 2012 05:21:26 PM H. Peter Anvin wrote:
> On 07/18/2012 03:36 AM, Thomas Renninger wrote:
> > cpio parsing code comes from  H. Peter Anvin.
> > The CONFIG_EARLY_INITRD feature is architecture independent, but
> > for now only enabled/called for X86.
> > The problem is that initrd_start must be valid, but there is no
> > architecture independent reserve_initrd() call in init/main.c or
> > similiar.
> > + * Add here new callback functions and the path relevant files show up in an
> > + * uncompressed cpio
> > + */
> > +static __initdata struct initrd_early_data initrd_early_callbacks[] =
> > +{
> > +	{
> > +		.namesp = NULL,
> > +	}
> > +};
> > +
> 
> I don't like your callback interface at all.  In fact, it is actively 
> broken, because it assumes that all early users are runnable at the same 
> time,
That's wrong.
If you have a closer look at the "ACPI table override" solution, it's
splitted up:
The callback collects all initrd provided tables:
    __init acpi_initrd_table_override() and __init acpi_initrd_finalize()
the actual usage of the files can happen any time later on when
the ACPICA subsystems grabs another table.

This is the most flexible solution and I cannot see why others
cannot do the same.

> which is trivially shown false -- the microcode work that Fenghua 
> Yu is working on needs access to its early data much, much earlier than 
> your ACPI code.
This is another problem and I expect I call:
early_initrd_find_cpio_data()
early enough for Fenghua's needs.
If not, how early exactly is this needed?

I hook in shortly after initrd_start gets valid.
This is necessary so that early_initrd_find_cpio_data can make
use of the arch independent initrd_start variable and the whole
feature is kept arch independent:

@@ -941,6 +941,8 @@ void __init setup_arch(char **cmdline_p)
 
        reserve_initrd();
 
+       early_initrd_find_cpio_data((void *)initrd_start, initrd_end - initrd_start);
+

I have heard about a possible use case on ARM for this (pass device tree
via initrd). I will ask...

> So big NAK on this change.  Instead we should stick to the imperative 
> interface that I had in my original code (call the search function with 
> a filename and let it return a pointer if found.)
This does not work with what I like to achive with APCI table overriding:
Pass an arbitrary amount of firmware files.
It could work with pre-defining the files, but that is not nice:
.../acpi0.aml
..
.../acpi9.aml

Another advantage:
If (just an example) CPU microcode files get passed via "early initrd",
the same path could be provided than needed by request_fw().
For Intel CPU microcode that would be:
/lib/firmware/intel-ucode
and files are split up there into family-model-stepping as done
already by microcode_intel.c
This would allow (with my approach):
   1) One can build a CPU family-model-stepping independent,
      generic initrd putting in all available Intel CPU microcodes.
   2) The path in cpio accessed via "uncompressed early initrd"
      can be the same as in the later unpacked rootfs accessed
      by initrd userspace tools.
      No need to add them twice, to the compressed and uncompressed
      cpio if the files should be available as "early initrd" data
      *and* in initramfs.      
      So above CPU microcode files could be used via "early initrd"
      mechanism to flash the boot CPU. And the same file(s) can be used
      later in unpacked intramfs via request_fw() to flash other, later
      brought up CPUs.
   3) ...


-> I'd prefer to go with this more flexible callback approach, instead
of spreading initrd_findcpio(..) calls all over the kernel when this gets
used more often.

   Thomas

Re: [PATCH 1/2] init: Introduce early initrd files through uncompressed cpio passing

[Thomas Renninger]

On Saturday, July 21, 2012 05:21:26 PM H. Peter Anvin wrote:
> On 07/18/2012 03:36 AM, Thomas Renninger wrote:
> > cpio parsing code comes from  H. Peter Anvin.
> > The CONFIG_EARLY_INITRD feature is architecture independent, but
> > for now only enabled/called for X86.
> > The problem is that initrd_start must be valid, but there is no
> > architecture independent reserve_initrd() call in init/main.c or
> > similiar.
> > + * Add here new callback functions and the path relevant files show up in an
> > + * uncompressed cpio
> > + */
> > +static __initdata struct initrd_early_data initrd_early_callbacks[] =
> > +{
> > +	{
> > +		.namesp = NULL,
> > +	}
> > +};
> > +
> 
> I don't like your callback interface at all.  In fact, it is actively 
> broken, because it assumes that all early users are runnable at the same 
> time,
That's wrong.
If you have a closer look at the "ACPI table override" solution, it's
splitted up:
The callback collects all initrd provided tables:
    __init acpi_initrd_table_override() and __init acpi_initrd_finalize()
the actual usage of the files can happen any time later on when
the ACPICA subsystems grabs another table.

This is the most flexible solution and I cannot see why others
cannot do the same.

> which is trivially shown false -- the microcode work that Fenghua 
> Yu is working on needs access to its early data much, much earlier than 
> your ACPI code.
This is another problem and I expect I call:
early_initrd_find_cpio_data()
early enough for Fenghua's needs.
If not, how early exactly is this needed?

I hook in shortly after initrd_start gets valid.
This is necessary so that early_initrd_find_cpio_data can make
use of the arch independent initrd_start variable and the whole
feature is kept arch independent:

@@ -941,6 +941,8 @@ void __init setup_arch(char **cmdline_p)
 
        reserve_initrd();
 
+       early_initrd_find_cpio_data((void *)initrd_start, initrd_end - initrd_start);
+

I have heard about a possible use case on ARM for this (pass device tree
via initrd). I will ask...

> So big NAK on this change.  Instead we should stick to the imperative 
> interface that I had in my original code (call the search function with 
> a filename and let it return a pointer if found.)
This does not work with what I like to achive with APCI table overriding:
Pass an arbitrary amount of firmware files.
It could work with pre-defining the files, but that is not nice:
.../acpi0.aml
..
.../acpi9.aml

Another advantage:
If (just an example) CPU microcode files get passed via "early initrd",
the same path could be provided than needed by request_fw().
For Intel CPU microcode that would be:
/lib/firmware/intel-ucode
and files are split up there into family-model-stepping as done
already by microcode_intel.c
This would allow (with my approach):
   1) One can build a CPU family-model-stepping independent,
      generic initrd putting in all available Intel CPU microcodes.
   2) The path in cpio accessed via "uncompressed early initrd"
      can be the same as in the later unpacked rootfs accessed
      by initrd userspace tools.
      No need to add them twice, to the compressed and uncompressed
      cpio if the files should be available as "early initrd" data
      *and* in initramfs.      
      So above CPU microcode files could be used via "early initrd"
      mechanism to flash the boot CPU. And the same file(s) can be used
      later in unpacked intramfs via request_fw() to flash other, later
      brought up CPUs.
   3) ...


-> I'd prefer to go with this more flexible callback approach, instead
of spreading initrd_findcpio(..) calls all over the kernel when this gets
used more often.

   Thomas

Re: [PATCH 1/2] init: Introduce early initrd files through uncompressed cpio passing

[H. Peter Anvin]

On 07/23/2012 07:40 AM, Thomas Renninger wrote:
> This is another problem and I expect I call:
> early_initrd_find_cpio_data()
> early enough for Fenghua's needs.
> If not, how early exactly is this needed?

We're calling that from arch-specific code before even turning paging 
on.  This has a couple of consequences:

1. ALL STATIC POINTERS ARE FORBIDDEN.  Period.  The code must be able to 
be executed from a nonstandard linear address, and any static pointer 
(like a function pointer) breaks that.

2. Any ideas of doing everything at the same time, or uniform 
architecture, is clearly out the window... we're just barely capable of 
using C at this point at all.

Now, you definitely do have a valid point about being able to iterate 
over multiple files with a common prefix.  We could do that with either 
a callback (where the callback is passed in as an argument), but I think 
it might be nicer to do that as an iterator interface... let me ketch on 
this.

> If (just an example) CPU microcode files get passed via "early initrd",
> the same path could be provided than needed by request_fw().

This will all be obsolete.  request_fw is available way, way, way too late.


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

Re: [PATCH 1/2] init: Introduce early initrd files through uncompressed cpio passing

[Thomas Renninger]

On Monday, July 23, 2012 05:09:16 PM H. Peter Anvin wrote:
> On 07/23/2012 07:40 AM, Thomas Renninger wrote:
> > This is another problem and I expect I call:
> > early_initrd_find_cpio_data()
> > early enough for Fenghua's needs.
> > If not, how early exactly is this needed?
> 
> We're calling that from arch-specific code before even turning paging 
> on.
Why?
If you would shed more light into what you (or Fenghua)
try to achieve that would help.
What kind of platform/CPU is this?
What happens if firmware is not provided (that early,..)?

...

> Now, you definitely do have a valid point about being able to iterate 
> over multiple files with a common prefix.  We could do that with either 
> a callback (where the callback is passed in as an argument), but I think 
> it might be nicer to do that as an iterator interface... let me ketch on 
> this.
Please do.

I finally would like to have the ACPI table via initird overriding.
ACPICA people added the physical table override stuff only for this.
With the cpio encapsulation (using initrd_start) this is a nice,
arch independent approach.
I can imagine the one or other arch picks this up. One example
could be flattened device tree passing via intird for ARM.

Maybe it could be kept arch independent with a "weird archs need things
even earlier" specific interface/hook if really needed.
Then others could pass initrd_start as now done, but X86 or
specific archs do some nasty HW specific stuff.

...
 
Hm, I could imagine this early fiddling will take some time.
If the cpio encapsulation as shown is acceptable, these patches
could get pushed already and the "very very early" additions can
be pushed on top in one of the next kernel rounds.

Thanks,

   Thomas

[PATCH 2/2] ACPI: Override arbitrary ACPI tables via initrd for debugging

[Thomas Renninger]

Details can be found in:
Documentation/acpi/initrd_table_override.txt

Signed-off-by: Thomas Renninger <trenn@suse.de>
CC: eric.piel@tremplin-utc.net
CC: vojcek@tlen.pl
CC: Lin Ming <ming.m.lin@intel.com>
CC: lenb@kernel.org
CC: robert.moore@intel.com
CC: hpa@zytor.com
---
 Documentation/acpi/initrd_table_override.txt |  119 ++++++++++++++++
 drivers/acpi/Kconfig                         |   10 ++
 drivers/acpi/osl.c                           |  193 ++++++++++++++++++++++++--
 include/linux/acpi.h                         |    6 +
 include/linux/initrd.h                       |    4 +-
 init/initramfs.c                             |   23 +++-
 init/initrd_early.c                          |   10 ++
 7 files changed, 349 insertions(+), 16 deletions(-)
 create mode 100644 Documentation/acpi/initrd_table_override.txt

diff --git a/Documentation/acpi/initrd_table_override.txt b/Documentation/acpi/initrd_table_override.txt
new file mode 100644
index 0000000..e985dea
--- /dev/null
+++ b/Documentation/acpi/initrd_table_override.txt
@@ -0,0 +1,119 @@
+Overriding ACPI tables via initrd
+=================================
+
+1) Introduction (What is this about)
+2) What is this for
+3) How does it work
+4) References (Where to retrieve userspace tools)
+
+1) What is this about
+---------------------
+
+If ACPI_INITRD_TABLE_OVERRIDE compile option is true, it is possible to
+override nearly any ACPI table provided by the BIOS with an instrumented,
+modified one.
+
+For a full list of ACPI tables that can be overridden, take a look at
+the char *table_sigs[MAX_ACPI_SIGNATURE]; definition in drivers/acpi/osl.c
+All ACPI tables iasl (Intel's ACPI compiler and disassembler) knows should
+be overridable, except:
+   - ACPI_SIG_RSDP (has a signature of 6 bytes)
+   - ACPI_SIG_FACS (does not have an ordinary ACPI table header)
+Both could get implemented as well.
+
+
+2) What is this for
+-------------------
+
+Please keep in mind that this is a debug option.
+ACPI tables should not get overridden for productive use.
+If BIOS ACPI tables are overridden the kernel will get tainted with the
+TAINT_OVERRIDDEN_ACPI_TABLE flag.
+Complain to your platform/BIOS vendor if you find a bug which is that sever
+that a workaround is not accepted in the Linus kernel.
+
+Still, it can and should be enabled in any kernel, because:
+  - There is no functional change with not instrumented initrds
+  - It provides a powerful feature to easily debug and test ACPI BIOS table
+    compatibility with the Linux kernel.
+
+Until now it was only possible to override the DSDT by compiling it into
+the kernel. This is a nightmare when trying to work on ACPI related bugs
+and a lot bugs got stuck because of that.
+Even for people with enough kernel knowledge, building a kernel to try out
+things is very time consuming. Also people may have to browse and modify the
+ACPI interpreter code to find a possible BIOS bug. With this feature, people
+can correct the ACPI tables and try out quickly whether this is the root cause
+that needs to get addressed in the kernel.
+
+This could even ease up testing for BIOS providers who could flush their BIOS
+to test, but overriding table via initrd is much easier and quicker.
+For example one could prepare different initrds overriding NUMA tables with
+different affinity settings. Set up a script, let the machine reboot and
+run tests over night and one can get a picture how these settings influence
+the Linux kernel and which values are best.
+
+People can instrument the dynamic ACPI (ASL) code (for example with debug
+statements showing up in syslog when the ACPI code is processed, etc.),
+to better understand BIOS to OS interfaces, to hunt down ACPI BIOS code related
+bugs quickly or to easier develop ACPI based drivers.
+
+Intstrumenting ACPI code in SSDTs is now much easier. Before, one had to copy
+all SSDTs into the DSDT to compile it into the kernel for testing
+(because only DSDT could get overridden). That's what the acpi_no_auto_ssdt
+boot param is for: the BIOS provided SSDTs are ignored and all have to get
+copied into the DSDT, complicated and time consuming.
+
+Much more use cases, depending on which ACPI parts you are working on...
+
+
+3) How does it work
+-------------------
+
+# Extract the machine's ACPI tables:
+acpidump >acpidump
+acpixtract -a acpidump
+# Disassemble, modify and recompile them:
+iasl -d *.dat
+# For example add this statement into a _PRT (PCI Routing Table) function
+# of the DSDT:
+Store("Hello World", debug)
+iasl -sa *.dsl
+# Add the raw ACPI tables to an uncompressed cpio archive.
+# They must be put into /kernel/firmware/acpi directory inside the cpio
+# archive.
+# If you want to override other firmware files early (for example CPU
+# microcode), you must use only one uncompressed cpio archive and it must
+# be the first. Other, typically compressed cpio archives, must be
+# concatenated on top of the uncompressed one.
+# For further info read the "Accessing initrd data early" chapter in
+# Documtenation/initrd.txt.
+mkdir -p /tmp/early_cpio/kernel/firmware/acpi
+cp TBL1.dat /tmp/early_cpio/kernel/firmware/acpi
+cat TBL2.dat /tmp/early_cpio/kernel/firmware/acpi
+cat TBL3.dat /tmp/early_cpio/kernel/firmware/acpi
+cd /tmp/early_cpio
+find . | cpio -H newc --create > /boot/instrumented_initrd
+cat /boot/initrd >>/boot/instrumented_initrd
+# reboot with increased acpi debug level, e.g. boot params:
+acpi.debug_level=0x2 acpi.debug_layer=0xFFFFFFFF
+# and check your syslog:
+[    1.268089] ACPI: PCI Interrupt Routing Table [\_SB_.PCI0._PRT]
+[    1.272091] [ACPI Debug]  String [0x0B] "HELLO WORLD"
+
+iasl is able to disassemble and recompile quite a lot different,
+also static ACPI tables.
+
+4) Where to retrieve userspace tools
+------------------------------------
+
+iasl and acpixtract are part of Intel's ACPICA project:
+http://acpica.org/
+and should be packaged by distributions (for example in the acpica package
+on SUSE).
+
+acpidump can be found in Len Browns pmtools:
+ftp://kernel.org/pub/linux/kernel/people/lenb/acpi/utils/pmtools/acpidump
+This tool is also part of the acpica package on SUSE.
+Alternatively used ACPI tables can be retrieved via sysfs in latest kernels:
+/sys/firmware/acpi/tables
diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index 8099895..9d49efb 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig
@@ -261,6 +261,16 @@ config ACPI_CUSTOM_DSDT
 	bool
 	default ACPI_CUSTOM_DSDT_FILE != ""
 
+config ACPI_INITRD_TABLE_OVERRIDE
+	bool
+	depends on EARLY_INITRD
+	default y
+	help
+	  This option provides functionality to override arbitrary ACPI tables
+	  via initrd. No functional change if no ACPI tables are passed via
+	  initrd, therefore it's safe to say Y.
+	  See Documentation/acpi/initrd_table_override.txt for details
+
 config ACPI_BLACKLIST_YEAR
 	int "Disable ACPI for systems before Jan 1st this year" if X86_32
 	default 0
diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
index c3881b2..059be34 100644
--- a/drivers/acpi/osl.c
+++ b/drivers/acpi/osl.c
@@ -45,6 +45,7 @@
 #include <linux/list.h>
 #include <linux/jiffies.h>
 #include <linux/semaphore.h>
+#include <linux/memblock.h>
 
 #include <asm/io.h>
 #include <asm/uaccess.h>
@@ -534,6 +535,126 @@ acpi_os_predefined_override(const struct acpi_predefined_names *init_val,
 	return AE_OK;
 }
 
+#ifdef CONFIG_ACPI_INITRD_TABLE_OVERRIDE
+#include <asm/e820.h>
+
+#define ACPI_OVERRIDE_TABLES 10
+
+__initdata static struct{
+	void *data;
+	int size;
+} early_initrd_files[ACPI_OVERRIDE_TABLES];
+static __initdata int table_nr;
+static int all_tables_size;
+static u64 acpi_tables_addr;
+
+/* Copied from acpica/tbutils.c:acpi_tb_checksum() */
+u8 __init acpi_table_checksum(u8 *buffer, u32 length)
+{
+	u8 sum = 0;
+	u8 *end = buffer + length;
+
+	while (buffer < end)
+		sum = (u8) (sum + *(buffer++));
+	return sum;
+}
+
+/* All but ACPI_SIG_RSDP and ACPI_SIG_FACS: */
+static const char *table_sigs[] = {
+	ACPI_SIG_BERT, ACPI_SIG_CPEP, ACPI_SIG_ECDT, ACPI_SIG_EINJ,
+	ACPI_SIG_ERST, ACPI_SIG_HEST, ACPI_SIG_MADT, ACPI_SIG_MSCT,
+	ACPI_SIG_SBST, ACPI_SIG_SLIT, ACPI_SIG_SRAT, ACPI_SIG_ASF,
+	ACPI_SIG_BOOT, ACPI_SIG_DBGP, ACPI_SIG_DMAR, ACPI_SIG_HPET,
+	ACPI_SIG_IBFT, ACPI_SIG_IVRS, ACPI_SIG_MCFG, ACPI_SIG_MCHI,
+	ACPI_SIG_SLIC, ACPI_SIG_SPCR, ACPI_SIG_SPMI, ACPI_SIG_TCPA,
+	ACPI_SIG_UEFI, ACPI_SIG_WAET, ACPI_SIG_WDAT, ACPI_SIG_WDDT,
+	ACPI_SIG_WDRT, ACPI_SIG_DSDT, ACPI_SIG_FADT, ACPI_SIG_PSDT,
+	ACPI_SIG_RSDT, ACPI_SIG_XSDT, ACPI_SIG_SSDT, NULL };
+
+/* Non-fatal errors: Affected tables/files are ignored */
+#define INVALID_TABLE(x, name) \
+	{ printk(KERN_ERR "ACPI OVERRIDE: " x " [%s]\n", name); return 1; }
+
+#define ACPI_HEADER_SIZE sizeof(struct acpi_table_header)
+
+int __init acpi_initrd_table_override(void *data, int size, const char *name)
+{
+	int sig;
+	struct acpi_table_header *table;
+
+	if (table_nr >= ACPI_OVERRIDE_TABLES)
+		INVALID_TABLE("Too much early tables - ignoring", name);
+
+	if (size < sizeof(struct acpi_table_header))
+		INVALID_TABLE("Table smaller than ACPI header", name);
+
+	table = data;
+
+	for (sig = 0; table_sigs[sig]; sig++)
+		if (!memcmp(table->signature, table_sigs[sig], 4))
+			break;
+
+	if (!table_sigs[sig])
+		INVALID_TABLE("Unknown signature", name);
+
+	if (size != table->length)
+		INVALID_TABLE("File length does not match table length", name);
+
+	if (acpi_table_checksum(data, table->length))
+		INVALID_TABLE("Bad table checksum", name);
+
+	printk(KERN_INFO "%4.4s ACPI table found in initrd [%s][%d]\n",
+	       table->signature, name, table->length);
+
+	all_tables_size += table->length;
+	early_initrd_files[table_nr].data =  data;
+	early_initrd_files[table_nr].size =  size;
+	table_nr++;
+	return 0;
+}
+
+void __init acpi_initrd_finalize(void)
+{
+	int i, offset = 0;
+	char *p;
+
+	acpi_tables_addr =
+		memblock_find_in_range(0, max_low_pfn_mapped << PAGE_SHIFT,
+				       all_tables_size, PAGE_SIZE);
+	if (!acpi_tables_addr)
+		panic("Cannot find place for ACPI override tables\n");
+
+	/*
+	 * Only calling e820_add_reserve does not work and the
+	 * tables are invalid (memory got used) later.
+	 * memblock_x86_reserve_range works as expected and the tables
+	 * won't get modified. But it's not enough because ioremap will
+	 * complain later (used by acpi_os_map_memory) that the pages
+	 * that should get mapped are not marked "reserved".
+	 * Both memblock_x86_reserve_range and e820_add_region works fine.
+	 */
+	memblock_reserve(acpi_tables_addr, acpi_tables_addr + all_tables_size);
+	e820_add_region(acpi_tables_addr, all_tables_size, E820_ACPI);
+	update_e820();
+	p = early_ioremap(acpi_tables_addr, all_tables_size);
+
+	for (i = 0; i < table_nr; i++) {
+		memcpy(p + offset, early_initrd_files[i].data,
+		       early_initrd_files[i].size);
+		offset += early_initrd_files[i].size;
+	}
+	early_iounmap(p, all_tables_size);
+}
+#endif /* CONFIG_ACPI_INITRD_TABLE_OVERRIDE */
+
+static void acpi_table_taint(struct acpi_table_header *table)
+{
+	printk(KERN_WARNING PREFIX "Override [%4.4s-%8.8s], "
+	       "this is unsafe: tainting kernel\n",
+	       table->signature, table->oem_table_id);
+	add_taint(TAINT_OVERRIDDEN_ACPI_TABLE);
+}	
+
 acpi_status
 acpi_os_table_override(struct acpi_table_header * existing_table,
 		       struct acpi_table_header ** new_table)
@@ -547,24 +668,74 @@ acpi_os_table_override(struct acpi_table_header * existing_table,
 	if (strncmp(existing_table->signature, "DSDT", 4) == 0)
 		*new_table = (struct acpi_table_header *)AmlCode;
 #endif
-	if (*new_table != NULL) {
-		printk(KERN_WARNING PREFIX "Override [%4.4s-%8.8s], "
-			   "this is unsafe: tainting kernel\n",
-		       existing_table->signature,
-		       existing_table->oem_table_id);
-		add_taint(TAINT_OVERRIDDEN_ACPI_TABLE);
-	}
+	if (*new_table != NULL)
+		acpi_table_taint(existing_table);
 	return AE_OK;
 }
 
 acpi_status
 acpi_os_physical_table_override(struct acpi_table_header *existing_table,
-				acpi_physical_address * new_address,
-				u32 *new_table_length)
+				acpi_physical_address *address,
+				u32 *table_length)
 {
-	return AE_SUPPORT;
-}
+#ifndef CONFIG_ACPI_INITRD_TABLE_OVERRIDE
+	*table_length = 0;
+	*address = 0;
+	return AE_OK;
+#else
+	int table_offset = 0;
+	struct acpi_table_header *table;
+
+	*table_length = 0;
+	*address = 0;
+
+	if (!acpi_tables_addr)
+		return AE_OK;
+
+	do {
+		if (table_offset + ACPI_HEADER_SIZE > all_tables_size) {
+			WARN_ON(1);
+			return AE_OK;
+		}
+
+		table = acpi_os_map_memory(acpi_tables_addr + table_offset,
+					   ACPI_HEADER_SIZE);
 
+		if (table_offset + table->length > all_tables_size) {
+			acpi_os_unmap_memory(table, ACPI_HEADER_SIZE);
+			WARN_ON(1);
+			return AE_OK;
+		}
+
+		table_offset += table->length;
+
+		if (memcmp(existing_table->signature, table->signature, 4)) {
+			acpi_os_unmap_memory(table,
+				     ACPI_HEADER_SIZE);
+			continue;
+		}
+
+		/* Only override tables with matching oem id */
+		if (memcmp(table->oem_table_id, existing_table->oem_table_id,
+			   ACPI_OEM_TABLE_ID_SIZE)) {
+			acpi_os_unmap_memory(table,
+				     ACPI_HEADER_SIZE);
+			continue;
+		}
+
+		table_offset -= table->length;
+		*table_length = table->length;
+		acpi_os_unmap_memory(table, ACPI_HEADER_SIZE);
+		*address = acpi_tables_addr + table_offset;
+		add_taint(TAINT_OVERRIDDEN_ACPI_TABLE);
+		break;
+	} while (table_offset + ACPI_HEADER_SIZE < all_tables_size);
+
+	if (*address != 0)
+		acpi_table_taint(existing_table);
+	return AE_OK;
+#endif
+}		
 
 static irqreturn_t acpi_irq(int irq, void *dev_id)
 {
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index f421dd8..9fb292c 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -76,6 +76,12 @@ typedef int (*acpi_table_handler) (struct acpi_table_header *table);
 
 typedef int (*acpi_table_entry_handler) (struct acpi_subtable_header *header, const unsigned long end);
 
+#ifdef CONFIG_ACPI_INITRD_TABLE_OVERRIDE
+int __init acpi_initrd_table_override(void *data,
+			      int size, const char *name);
+void __init acpi_initrd_finalize(void);
+#endif
+
 char * __acpi_map_table (unsigned long phys_addr, unsigned long size);
 void __acpi_unmap_table(char *map, unsigned long size);
 int early_acpi_boot_init(void);
diff --git a/include/linux/initrd.h b/include/linux/initrd.h
index 3fe262e..8b26e4d 100644
--- a/include/linux/initrd.h
+++ b/include/linux/initrd.h
@@ -23,9 +23,9 @@ extern unsigned int real_root_dev;
 #define MAX_EARLY_INITRD_CB 16
 
 #ifdef CONFIG_EARLY_INITRD
-extern int early_initrd_find_cpio_data(const char *data, size_t len);
+extern void early_initrd_find_cpio_data(const char *data, size_t len);
 #else
-static int early_initrd_find_cpio_data(const char *data, size_t len)
+static void early_initrd_find_cpio_data(const char *data, size_t len)
 {
 	return 0;
 }
diff --git a/init/initramfs.c b/init/initramfs.c
index 84c6bf1..70a1972 100644
--- a/init/initramfs.c
+++ b/init/initramfs.c
@@ -411,8 +411,10 @@ static int __init flush_buffer(void *bufv, unsigned len)
 			buf += written;
 			len -= written;
 			state = Reset;
-		} else
+		} else {
+			pr_info("junk in compressed archive 3 %u", len);
 			error("junk in compressed archive");
+		}
 	}
 	return origLen;
 }
@@ -427,6 +429,10 @@ static char * __init unpack_to_rootfs(char *buf, unsigned len)
 	decompress_fn decompress;
 	const char *compress_name;
 	static __initdata char msg_buf[64];
+	int skipped = 0;
+	unsigned long tot_written = 0;
+
+	pr_info("%s: 0x%p len: %u\n", __FUNCTION__, buf, len);
 
 	header_buf = kmalloc(110, GFP_KERNEL);
 	symlink_buf = kmalloc(PATH_MAX + N_ALIGN(PATH_MAX) + 1, GFP_KERNEL);
@@ -441,13 +447,17 @@ static char * __init unpack_to_rootfs(char *buf, unsigned len)
 	while (!message && len) {
 		loff_t saved_offset = this_header;
 		if (*buf == '0' && !(this_header & 3)) {
+			pr_info("Starting...\n");
 			state = Start;
 			written = write_buffer(buf, len);
 			buf += written;
 			len -= written;
+			pr_info("... %u written, remaining: %u\n",
+				written, len);
 			continue;
 		}
 		if (!*buf) {
+			skipped++;
 			buf++;
 			len--;
 			this_header++;
@@ -456,21 +466,28 @@ static char * __init unpack_to_rootfs(char *buf, unsigned len)
 		this_header = 0;
 		decompress = decompress_method(buf, len, &compress_name);
 		if (decompress) {
+			pr_info("Decompress: %u - buf[0]: 0x%x - buf[1]: 0x%x", len, *buf, *(buf + 1));
+			pr_info("Decompressing via %s\n", compress_name);
 			res = decompress(buf, len, NULL, flush_buffer, NULL,
 				   &my_inptr, error);
 			if (res)
 				error("decompressor failed");
 		} else if (compress_name) {
+			pr_info("Not decompressing via %s\n", compress_name);
 			if (!message) {
 				snprintf(msg_buf, sizeof msg_buf,
 					 "compression method %s not configured",
 					 compress_name);
 				message = msg_buf;
 			}
-		} else
+		} else {
+			pr_info("junk in compressed archive 1 %u - buf[0]: 0x%x - buf[1]: 0x%x", len, *buf, *(buf + 1));
 			error("junk in compressed archive");
-		if (state != Reset)
+		}
+		if (state != Reset) {
+			pr_info("junk in compressed archive 2 %u", len);
 			error("junk in compressed archive");
+		}
 		this_header = saved_offset + my_inptr;
 		buf += my_inptr;
 		len -= my_inptr;
diff --git a/init/initrd_early.c b/init/initrd_early.c
index c657a4b..35d8480 100644
--- a/init/initrd_early.c
+++ b/init/initrd_early.c
@@ -1,6 +1,9 @@
 #include <linux/kernel.h>
 #include <linux/string.h>
 #include <linux/initrd.h>
+#ifdef CONFIG_ACPI_INITRD_TABLE_OVERRIDE
+#include <linux/acpi.h>
+#endif
 
 struct initrd_early_data {
 	/* Path where relevant files can be found in uncompressed cpio */
@@ -18,6 +21,13 @@ struct initrd_early_data {
  */
 static __initdata struct initrd_early_data initrd_early_callbacks[] =
 {
+#ifdef CONFIG_ACPI_INITRD_TABLE_OVERRIDE
+	{
+		.namesp = "kernel/firmware/acpi/",
+		.cb     = acpi_initrd_table_override,
+		.final  = acpi_initrd_finalize,
+	},
+#endif
 	{
 		.namesp = NULL,
 	}
-- 
1.7.6.1