diff options
| author | Steven Rostedt (Google) <rostedt@goodmis.org> | 2024-06-13 11:55:07 -0400 |
|---|---|---|
| committer | Mike Rapoport (IBM) <rppt@kernel.org> | 2024-06-19 10:59:49 +0300 |
| commit | 1e4c64b71c9bf230b25fde12cbcceacfdc8b3332 (patch) | |
| tree | 20c8fdee1895eb8d8ab6701ab64d584d11f28f9a /Documentation/admin-guide | |
| parent | 0e9899feed9cbb7d33c01ad849dc307b1560b0ab (diff) | |
mm/memblock: Add "reserve_mem" to reserved named memory at boot up
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>
Link: https://lore.kernel.org/r/20240613155527.437020271@goodmis.org
Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>
Diffstat (limited to 'Documentation/admin-guide')
| -rw-r--r-- | Documentation/admin-guide/kernel-parameters.txt | 22 |
1 files changed, 22 insertions, 0 deletions
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 |