docs/kernel-parameters: update description of mem=

The existing description of mem= does not cover all the cases and
differences between how architectures treat it.

Extend the description to match the code.

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Link: https://lore.kernel.org/r/20220310082736.1346366-1-rppt@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index f5a27f0..5b84cca 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2827,6 +2827,9 @@
 
                        For details see: Documentation/admin-guide/hw-vuln/mds.rst
 
+       mem=nn[KMG]     [HEXAGON] Set the memory size.
+                       Must be specified, otherwise memory size will be 0.
+
        mem=nn[KMG]     [KNL,BOOT] Force usage of a specific amount of memory
                        Amount of memory to be used in cases as follows:
 
@@ -2834,6 +2837,13 @@
                        2 when the kernel is not able to see the whole system memory;
                        3 memory that lies after 'mem=' boundary is excluded from
                         the hypervisor, then assigned to KVM guests.
+                       4 to limit the memory available for kdump kernel.
+
+                       [ARC,MICROBLAZE] - the limit applies only to low memory,
+                       high memory is not affected.
+
+                       [ARM64] - only limits memory covered by the linear
+                       mapping. The NOMAP regions are not affected.
 
                        [X86] Work as limiting max address. Use together
                        with memmap= to avoid physical address space collisions.
@@ -2844,6 +2854,14 @@
                        in above case 3, memory may need be hot added after boot
                        if system memory of hypervisor is not sufficient.
 
+       mem=nn[KMG]@ss[KMG]
+                       [ARM,MIPS] - override the memory layout reported by
+                       firmware.
+                       Define a memory region of size nn[KMG] starting at
+                       ss[KMG].
+                       Multiple different regions can be specified with
+                       multiple mem= parameters on the command line.
+
        mem=nopentium   [BUGS=X86-32] Disable usage of 4MB pages for kernel
                        memory.