[PATCH v7 0/2] mm/memblock: Add "reserve_mem" to reserved named memory at boot up

[PATCH v7 0/2] mm/memblock: Add "reserve_mem" to reserved named memory at boot up

[Steven Rostedt]

Reserve unspecified location of physical memory from kernel command line

Background:

In ChromeOS, we have 1 MB of pstore ramoops reserved so that we can extract
dmesg output and some other information when a crash happens in the field.
(This is only done when the user selects "Allow Google to collect data for
 improving the system"). But there are cases when there's a bug that
requires more data to be retrieved to figure out what is happening. We would
like to increase the pstore size, either temporarily, or maybe even
permanently. The pstore on these devices are at a fixed location in RAM (as
the RAM is not cleared on soft reboots nor crashes). The location is chosen
by the BIOS (coreboot) and passed to the kernel via ACPI tables on x86.
There's a driver that queries for this to initialize the pstore for
ChromeOS:

  See drivers/platform/chrome/chromeos_pstore.c

Problem:

The problem is that, even though there's a process to change the kernel on
these systems, and is done regularly to install updates, the firmware is
updated much less frequently. Choosing the place in RAM also takes special
care, and may be in a different address for different boards. Updating the
size via firmware is a large effort and not something that many are willing
to do for a temporary pstore size change.

Requirement:

Need a way to reserve memory that will be at a consistent location for
every boot, if the kernel and system are the same. Does not need to work
if rebooting to a different kernel, or if the system can change the
memory layout between boots.

The reserved memory can not be an hard coded address, as the same kernel /
command line needs to run on several different machines. The picked memory
reservation just needs to be the same for a given machine, but may be
different for different machines.

Solution:

The solution I have come up with is to introduce a new "reserve_mem=" kernel
command line. This parameter takes the following format:

  reserve_mem=nn:align:label

Where nn is the size of memory to reserve, the align is the alignment of
that memory, and label is the way for other sub-systems to find that memory.
This way the kernel command line could have:

  reserve_mem=12M:4096:oops   ramoops.mem_name=oops

At boot up, the kernel will search for 12 megabytes in usable memory regions
with an alignment of 4096. It will start at the highest regions and work its
way down (for those old devices that want access to lower address DMA). When
it finds a region, it will save it off in a small table and mark it with the
"oops" label. Then the pstore ramoops sub-system could ask for that memory
and location, and it will map itself there.

This prototype allows for 8 different mappings (which may be overkill, 4 is
probably plenty) with 16 byte size to store the label.

I have tested this and it works for us to solve the above problem. We can
update the kernel and command line and increase the size of pstore without
needing to update the firmware, or knowing every memory layout of each
board. I only tested this locally, it has not been tested in the field.

Changes since v6: https://lore.kernel.org/all/20240613155506.811013916@goodmis.org/

- Fixed typo of s/reserver/reserve/

Changes since v5: https://lore.kernel.org/all/20240613003435.401549779@goodmis.org/


- Stressed more that this is a best effort use case

- Updated ramoops.rst to document this new feature

- Used a new variable "tmp" to use in reserve_mem_find_by_name() instead
  of using "size" and possibly corrupting it.

Changes since v4: https://lore.kernel.org/all/20240611215610.548854415@goodmis.org/

- Add all checks about reserve_mem before allocation.
  This means reserved_mem_add() is now a void function.

- Check for name duplications.

- Fix compare of align to SMP_CACHE_BYTES ("<" instead of "<=")

Changes since v3: https://lore.kernel.org/all/20240611144911.327227285@goodmis.org/

- Changed table type of start and size from unsigned long to phys_addr_t
  (as well as the parameters to the functions that use them)

- Changed old reference to "early_reserve_mem" to "reserve_mem"

- Check before reservering memory:
  o Size is non-zero
  o name has text in it

- If align is less than SMP_CACHE_BYTES, make it SMP_CACHE_BYTES

- Remove the silly check of testing *p == '\0' after a p += strlen(p)

Changes since v2: https://lore.kernel.org/all/20240606150143.876469296@goodmis.org/

- Fixed typo of "reserver"

- Added EXPORT_SYMBOL_GPL() for reserve_mem_find_by_name()

- Removed "built-in" from module description that was changed from v1.


Changes since v1: https://lore.kernel.org/all/20240603233330.801075898@goodmis.org/

- Updated the change log of the first patch as well as added an entry
  into kernel-parameters.txt about how reserve_mem is for soft reboots
  and may not be reliable. 


Steven Rostedt (Google) (2):
      mm/memblock: Add "reserve_mem" to reserved named memory at boot up
      pstore/ramoops: Add ramoops.mem_name= command line option

----
 Documentation/admin-guide/kernel-parameters.txt |  22 +++++
 Documentation/admin-guide/ramoops.rst           |  13 +++
 fs/pstore/ram.c                                 |  14 +++
 include/linux/mm.h                              |   2 +
 mm/memblock.c                                   | 117 ++++++++++++++++++++++++
 5 files changed, 168 insertions(+)

[PATCH v7 1/2] mm/memblock: Add "reserve_mem" to reserved named memory at boot up

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

In order to allow for requesting a memory region that can be used for
things like pstore on multiple machines where the memory layout is not the
same, add a new option to the kernel command line called "reserve_mem".

The format is:  reserve_mem=nn:align:name

Where it will find nn amount of memory at the given alignment of align.
The name field is to allow another subsystem to retrieve where the memory
was found. For example:

  reserve_mem=12M:4096:oops ramoops.mem_name=oops

Where ramoops.mem_name will tell ramoops that memory was reserved for it
via the reserve_mem option and it can find it by calling:

  if (reserve_mem_find_by_name("oops", &start, &size)) {
	// start holds the start address and size holds the size given

This is typically used for systems that do not wipe the RAM, and this
command line will try to reserve the same physical memory on soft reboots.
Note, it is not guaranteed to be the same location. For example, if KASLR
places the kernel at the location of where the RAM reservation was from a
previous boot, the new reservation will be at a different location.  Any
subsystem using this feature must add a way to verify that the contents of
the physical memory is from a previous boot, as there may be cases where
the memory will not be located at the same location.

Not all systems may work either. There could be bit flips if the reboot
goes through the BIOS. Using kexec to reboot the machine is likely to
have better results in such cases.

Link: https://lore.kernel.org/all/ZjJVnZUX3NZiGW6q@kernel.org/

Suggested-by: Mike Rapoport <rppt@kernel.org>
Tested-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 .../admin-guide/kernel-parameters.txt         |  22 ++++
 include/linux/mm.h                            |   2 +
 mm/memblock.c                                 | 117 ++++++++++++++++++
 3 files changed, 141 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index b600df82669d..56e18b1a520d 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5710,6 +5710,28 @@
 			them.  If <base> is less than 0x10000, the region
 			is assumed to be I/O ports; otherwise it is memory.
 
+	reserve_mem=	[RAM]
+			Format: nn[KNG]:<align>:<label>
+			Reserve physical memory and label it with a name that
+			other subsystems can use to access it. This is typically
+			used for systems that do not wipe the RAM, and this command
+			line will try to reserve the same physical memory on
+			soft reboots. Note, it is not guaranteed to be the same
+			location. For example, if anything about the system changes
+			or if booting a different kernel. It can also fail if KASLR
+			places the kernel at the location of where the RAM reservation
+			was from a previous boot, the new reservation will be at a
+			different location.
+			Any subsystem using this feature must add a way to verify
+			that the contents of the physical memory is from a previous
+			boot, as there may be cases where the memory will not be
+			located at the same location.
+
+			The format is size:align:label for example, to request
+			12 megabytes of 4096 alignment for ramoops:
+
+			reserve_mem=12M:4096:oops ramoops.mem_name=oops
+
 	reservetop=	[X86-32,EARLY]
 			Format: nn[KMG]
 			Reserves a hole at the top of the kernel virtual
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 9849dfda44d4..077fb589b88a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4263,4 +4263,6 @@ static inline bool pfn_is_unaccepted_memory(unsigned long pfn)
 void vma_pgtable_walk_begin(struct vm_area_struct *vma);
 void vma_pgtable_walk_end(struct vm_area_struct *vma);
 
+int reserve_mem_find_by_name(const char *name, phys_addr_t *start, phys_addr_t *size);
+
 #endif /* _LINUX_MM_H */
diff --git a/mm/memblock.c b/mm/memblock.c
index d09136e040d3..b7b0e8c3868d 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -2244,6 +2244,123 @@ void __init memblock_free_all(void)
 	totalram_pages_add(pages);
 }
 
+/* Keep a table to reserve named memory */
+#define RESERVE_MEM_MAX_ENTRIES		8
+#define RESERVE_MEM_NAME_SIZE		16
+struct reserve_mem_table {
+	char			name[RESERVE_MEM_NAME_SIZE];
+	phys_addr_t		start;
+	phys_addr_t		size;
+};
+static struct reserve_mem_table reserved_mem_table[RESERVE_MEM_MAX_ENTRIES];
+static int reserved_mem_count;
+
+/* Add wildcard region with a lookup name */
+static void __init reserved_mem_add(phys_addr_t start, phys_addr_t size,
+				   const char *name)
+{
+	struct reserve_mem_table *map;
+
+	map = &reserved_mem_table[reserved_mem_count++];
+	map->start = start;
+	map->size = size;
+	strscpy(map->name, name);
+}
+
+/**
+ * reserve_mem_find_by_name - Find reserved memory region with a given name
+ * @name: The name that is attached to a reserved memory region
+ * @start: If found, holds the start address
+ * @size: If found, holds the size of the address.
+ *
+ * @start and @size are only updated if @name is found.
+ *
+ * Returns: 1 if found or 0 if not found.
+ */
+int reserve_mem_find_by_name(const char *name, phys_addr_t *start, phys_addr_t *size)
+{
+	struct reserve_mem_table *map;
+	int i;
+
+	for (i = 0; i < reserved_mem_count; i++) {
+		map = &reserved_mem_table[i];
+		if (!map->size)
+			continue;
+		if (strcmp(name, map->name) == 0) {
+			*start = map->start;
+			*size = map->size;
+			return 1;
+		}
+	}
+	return 0;
+}
+EXPORT_SYMBOL_GPL(reserve_mem_find_by_name);
+
+/*
+ * Parse reserve_mem=nn:align:name
+ */
+static int __init reserve_mem(char *p)
+{
+	phys_addr_t start, size, align, tmp;
+	char *name;
+	char *oldp;
+	int len;
+
+	if (!p)
+		return -EINVAL;
+
+	/* Check if there's room for more reserved memory */
+	if (reserved_mem_count >= RESERVE_MEM_MAX_ENTRIES)
+		return -EBUSY;
+
+	oldp = p;
+	size = memparse(p, &p);
+	if (!size || p == oldp)
+		return -EINVAL;
+
+	if (*p != ':')
+		return -EINVAL;
+
+	align = memparse(p+1, &p);
+	if (*p != ':')
+		return -EINVAL;
+
+	/*
+	 * memblock_phys_alloc() doesn't like a zero size align,
+	 * but it is OK for this command to have it.
+	 */
+	if (align < SMP_CACHE_BYTES)
+		align = SMP_CACHE_BYTES;
+
+	name = p + 1;
+	len = strlen(name);
+
+	/* name needs to have length but not too big */
+	if (!len || len >= RESERVE_MEM_NAME_SIZE)
+		return -EINVAL;
+
+	/* Make sure that name has text */
+	for (p = name; *p; p++) {
+		if (!isspace(*p))
+			break;
+	}
+	if (!*p)
+		return -EINVAL;
+
+	/* Make sure the name is not already used */
+	if (reserve_mem_find_by_name(name, &start, &tmp))
+		return -EBUSY;
+
+	start = memblock_phys_alloc(size, align);
+	if (!start)
+		return -ENOMEM;
+
+	reserved_mem_add(start, size, name);
+
+	return 0;
+}
+__setup("reserve_mem=", reserve_mem);
+
 #if defined(CONFIG_DEBUG_FS) && defined(CONFIG_ARCH_KEEP_MEMBLOCK)
 static const char * const flagname[] = {
 	[ilog2(MEMBLOCK_HOTPLUG)] = "HOTPLUG",
-- 
2.43.0

Re: [PATCH v7 1/2] mm/memblock: Add "reserve_mem" to reserved named memory at boot up

[Wei Yang]

On Thu, Jun 13, 2024 at 07:34:16PM -0400, Steven Rostedt wrote:
>From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
>
>In order to allow for requesting a memory region that can be used for
>things like pstore on multiple machines where the memory layout is not the
>same, add a new option to the kernel command line called "reserve_mem".
>
>The format is:  reserve_mem=nn:align:name
>
>Where it will find nn amount of memory at the given alignment of align.
>The name field is to allow another subsystem to retrieve where the memory
>was found. For example:
>
>  reserve_mem=12M:4096:oops ramoops.mem_name=oops
>
>Where ramoops.mem_name will tell ramoops that memory was reserved for it
>via the reserve_mem option and it can find it by calling:
>
>  if (reserve_mem_find_by_name("oops", &start, &size)) {
>	// start holds the start address and size holds the size given
>
>This is typically used for systems that do not wipe the RAM, and this
>command line will try to reserve the same physical memory on soft reboots.
>Note, it is not guaranteed to be the same location. For example, if KASLR
>places the kernel at the location of where the RAM reservation was from a
>previous boot, the new reservation will be at a different location.  Any
>subsystem using this feature must add a way to verify that the contents of
>the physical memory is from a previous boot, as there may be cases where
>the memory will not be located at the same location.
>
>Not all systems may work either. There could be bit flips if the reboot
>goes through the BIOS. Using kexec to reboot the machine is likely to
>have better results in such cases.
>
>Link: https://lore.kernel.org/all/ZjJVnZUX3NZiGW6q@kernel.org/
>
>Suggested-by: Mike Rapoport <rppt@kernel.org>
>Tested-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
>Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
>---
> .../admin-guide/kernel-parameters.txt         |  22 ++++
> include/linux/mm.h                            |   2 +
> mm/memblock.c                                 | 117 ++++++++++++++++++
> 3 files changed, 141 insertions(+)
>
>diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>index b600df82669d..56e18b1a520d 100644
>--- a/Documentation/admin-guide/kernel-parameters.txt
>+++ b/Documentation/admin-guide/kernel-parameters.txt
>@@ -5710,6 +5710,28 @@
> 			them.  If <base> is less than 0x10000, the region
> 			is assumed to be I/O ports; otherwise it is memory.
> 
>+	reserve_mem=	[RAM]
>+			Format: nn[KNG]:<align>:<label>
>+			Reserve physical memory and label it with a name that
>+			other subsystems can use to access it. This is typically
>+			used for systems that do not wipe the RAM, and this command
>+			line will try to reserve the same physical memory on
>+			soft reboots. Note, it is not guaranteed to be the same
>+			location. For example, if anything about the system changes
>+			or if booting a different kernel. It can also fail if KASLR
>+			places the kernel at the location of where the RAM reservation
>+			was from a previous boot, the new reservation will be at a
>+			different location.
>+			Any subsystem using this feature must add a way to verify
>+			that the contents of the physical memory is from a previous
>+			boot, as there may be cases where the memory will not be
>+			located at the same location.
>+
>+			The format is size:align:label for example, to request
>+			12 megabytes of 4096 alignment for ramoops:
>+
>+			reserve_mem=12M:4096:oops ramoops.mem_name=oops
>+
> 	reservetop=	[X86-32,EARLY]
> 			Format: nn[KMG]
> 			Reserves a hole at the top of the kernel virtual
>diff --git a/include/linux/mm.h b/include/linux/mm.h
>index 9849dfda44d4..077fb589b88a 100644
>--- a/include/linux/mm.h
>+++ b/include/linux/mm.h
>@@ -4263,4 +4263,6 @@ static inline bool pfn_is_unaccepted_memory(unsigned long pfn)
> void vma_pgtable_walk_begin(struct vm_area_struct *vma);
> void vma_pgtable_walk_end(struct vm_area_struct *vma);
> 
>+int reserve_mem_find_by_name(const char *name, phys_addr_t *start, phys_addr_t *size);
>+
> #endif /* _LINUX_MM_H */
>diff --git a/mm/memblock.c b/mm/memblock.c
>index d09136e040d3..b7b0e8c3868d 100644
>--- a/mm/memblock.c
>+++ b/mm/memblock.c
>@@ -2244,6 +2244,123 @@ void __init memblock_free_all(void)
> 	totalram_pages_add(pages);
> }
> 
>+/* Keep a table to reserve named memory */
>+#define RESERVE_MEM_MAX_ENTRIES		8
>+#define RESERVE_MEM_NAME_SIZE		16
>+struct reserve_mem_table {
>+	char			name[RESERVE_MEM_NAME_SIZE];
>+	phys_addr_t		start;
>+	phys_addr_t		size;
>+};
>+static struct reserve_mem_table reserved_mem_table[RESERVE_MEM_MAX_ENTRIES];
>+static int reserved_mem_count;
>+
>+/* Add wildcard region with a lookup name */
>+static void __init reserved_mem_add(phys_addr_t start, phys_addr_t size,
>+				   const char *name)
>+{

The logic looks good to me.

My concern now is the name may bring some confusion to others. We have
memblock.memory and memblock.reserved, without some careful reading users may
think this is used to add a region to memblock.reserved.

And the words with *reserve* may remind people of the concept related to
memblock.reserved.

Not good at naming, maybe "prealloc_mem"? Someone could differentiate it would
be better.

>+	struct reserve_mem_table *map;
>+
>+	map = &reserved_mem_table[reserved_mem_count++];
>+	map->start = start;
>+	map->size = size;
>+	strscpy(map->name, name);
>+}
>+
>+/**
>+ * reserve_mem_find_by_name - Find reserved memory region with a given name
>+ * @name: The name that is attached to a reserved memory region
>+ * @start: If found, holds the start address
>+ * @size: If found, holds the size of the address.
>+ *
>+ * @start and @size are only updated if @name is found.
>+ *
>+ * Returns: 1 if found or 0 if not found.
>+ */
>+int reserve_mem_find_by_name(const char *name, phys_addr_t *start, phys_addr_t *size)
>+{
>+	struct reserve_mem_table *map;
>+	int i;
>+
>+	for (i = 0; i < reserved_mem_count; i++) {
>+		map = &reserved_mem_table[i];
>+		if (!map->size)
>+			continue;
>+		if (strcmp(name, map->name) == 0) {
>+			*start = map->start;
>+			*size = map->size;
>+			return 1;
>+		}
>+	}
>+	return 0;
>+}
>+EXPORT_SYMBOL_GPL(reserve_mem_find_by_name);
>+
>+/*
>+ * Parse reserve_mem=nn:align:name
>+ */
>+static int __init reserve_mem(char *p)
>+{
>+	phys_addr_t start, size, align, tmp;
>+	char *name;
>+	char *oldp;
>+	int len;
>+
>+	if (!p)
>+		return -EINVAL;
>+
>+	/* Check if there's room for more reserved memory */
>+	if (reserved_mem_count >= RESERVE_MEM_MAX_ENTRIES)
>+		return -EBUSY;
>+
>+	oldp = p;
>+	size = memparse(p, &p);
>+	if (!size || p == oldp)
>+		return -EINVAL;
>+
>+	if (*p != ':')
>+		return -EINVAL;
>+
>+	align = memparse(p+1, &p);
>+	if (*p != ':')
>+		return -EINVAL;
>+
>+	/*
>+	 * memblock_phys_alloc() doesn't like a zero size align,
>+	 * but it is OK for this command to have it.
>+	 */
>+	if (align < SMP_CACHE_BYTES)
>+		align = SMP_CACHE_BYTES;
>+
>+	name = p + 1;
>+	len = strlen(name);
>+
>+	/* name needs to have length but not too big */
>+	if (!len || len >= RESERVE_MEM_NAME_SIZE)
>+		return -EINVAL;
>+
>+	/* Make sure that name has text */
>+	for (p = name; *p; p++) {
>+		if (!isspace(*p))
>+			break;
>+	}
>+	if (!*p)
>+		return -EINVAL;
>+
>+	/* Make sure the name is not already used */
>+	if (reserve_mem_find_by_name(name, &start, &tmp))
>+		return -EBUSY;
>+
>+	start = memblock_phys_alloc(size, align);
>+	if (!start)
>+		return -ENOMEM;
>+
>+	reserved_mem_add(start, size, name);
>+
>+	return 0;
>+}
>+__setup("reserve_mem=", reserve_mem);
>+
> #if defined(CONFIG_DEBUG_FS) && defined(CONFIG_ARCH_KEEP_MEMBLOCK)
> static const char * const flagname[] = {
> 	[ilog2(MEMBLOCK_HOTPLUG)] = "HOTPLUG",
>-- 
>2.43.0
>
>

-- 
Wei Yang
Help you, Help me

[PATCH v7 2/2] pstore/ramoops: Add ramoops.mem_name= command line option

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

Add a method to find a region specified by reserve_mem=nn:align:name for
ramoops. Adding a kernel command line parameter:

  reserve_mem=12M:4096:oops ramoops.mem_name=oops

Will use the size and location defined by the memmap parameter where it
finds the memory and labels it "oops". The "oops" in the ramoops option
is used to search for it.

This allows for arbitrary RAM to be used for ramoops if it is known that
the memory is not cleared on kernel crashes or soft reboots.

Tested-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 Documentation/admin-guide/ramoops.rst | 13 +++++++++++++
 fs/pstore/ram.c                       | 14 ++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/Documentation/admin-guide/ramoops.rst b/Documentation/admin-guide/ramoops.rst
index e9f85142182d..2eabef31220d 100644
--- a/Documentation/admin-guide/ramoops.rst
+++ b/Documentation/admin-guide/ramoops.rst
@@ -23,6 +23,8 @@ and type of the memory area are set using three variables:
   * ``mem_size`` for the size. The memory size will be rounded down to a
     power of two.
   * ``mem_type`` to specify if the memory type (default is pgprot_writecombine).
+  * ``mem_name`` to specify a memory region defined by ``reserve_mem`` command
+    line parameter.
 
 Typically the default value of ``mem_type=0`` should be used as that sets the pstore
 mapping to pgprot_writecombine. Setting ``mem_type=1`` attempts to use
@@ -118,6 +120,17 @@ Setting the ramoops parameters can be done in several different manners:
 	return ret;
   }
 
+ D. Using a region of memory reserved via ``reserve_mem`` command line
+    parameter. The address and size will be defined by the ``reserve_mem``
+    parameter. Note, that ``reserve_mem`` may not always allocate memory
+    in the same location, and cannot be relied upon. Testing will need
+    to be done, and it may not work on every machine, nor every kernel.
+    Consider this a "best effort" approach. The ``reserve_mem`` option
+    takes a size, alignment and name as arguments. The name is used
+    to map the memory to a label that can be retrieved by ramoops.
+
+	reserve_mem=2M:4096:oops  ramoops.mem_name=oops
+
 You can specify either RAM memory or peripheral devices' memory. However, when
 specifying RAM, be sure to reserve the memory by issuing memblock_reserve()
 very early in the architecture code, e.g.::
diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
index b1a455f42e93..4311fcbc84f2 100644
--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -50,6 +50,10 @@ module_param_hw(mem_address, ullong, other, 0400);
 MODULE_PARM_DESC(mem_address,
 		"start of reserved RAM used to store oops/panic logs");
 
+static char *mem_name;
+module_param_named(mem_name, mem_name, charp, 0400);
+MODULE_PARM_DESC(mem_name, "name of kernel param that holds addr");
+
 static ulong mem_size;
 module_param(mem_size, ulong, 0400);
 MODULE_PARM_DESC(mem_size,
@@ -914,6 +918,16 @@ static void __init ramoops_register_dummy(void)
 {
 	struct ramoops_platform_data pdata;
 
+	if (mem_name) {
+		phys_addr_t start;
+		phys_addr_t size;
+
+		if (reserve_mem_find_by_name(mem_name, &start, &size)) {
+			mem_address = start;
+			mem_size = size;
+		}
+	}
+
 	/*
 	 * Prepare a dummy platform data structure to carry the module
 	 * parameters. If mem_size isn't set, then there are no module
-- 
2.43.0