Commit f3cd4c86 authored by Baoquan He's avatar Baoquan He Committed by Linus Torvalds

mm/memory_hotplug.c: only respect mem= parameter during boot stage

In commit 357b4da5 ("x86: respect memory size limiting via mem=
parameter") a global varialbe max_mem_size is added to store the value
parsed from 'mem= ', then checked when memory region is added.  This truly
stops those DIMMs from being added into system memory during boot-time.

However, it also limits the later memory hotplug functionality.  Any DIMM
can't be hotplugged any more if its region is beyond the max_mem_size.  We
will get errors like:

[  216.387164] acpi PNP0C80:02: add_memory failed
[  216.389301] acpi PNP0C80:02: acpi_memory_enable_device() error
[  216.392187] acpi PNP0C80:02: Enumeration failure

This will cause issue in a known use case where 'mem=' is added to the
hypervisor.  The memory that lies after 'mem=' boundary will be assigned
to KVM guests.  After commit 357b4da5 merged, memory can't be extended
dynamically if system memory on hypervisor is not sufficient.

So fix it by also checking if it's during boot-time restricting to add
memory.  Otherwise, skip the restriction.

And also add this use case to document of 'mem=' kernel parameter.

Fixes: 357b4da5 ("x86: respect memory size limiting via mem= parameter")
Signed-off-by: default avatarBaoquan He <bhe@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: default avatarJuergen Gross <jgross@suse.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: William Kucharski <william.kucharski@oracle.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Link: http://lkml.kernel.org/r/20200204050643.20925-1-bhe@redhat.comSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent dccacf8d
...@@ -2573,13 +2573,22 @@ ...@@ -2573,13 +2573,22 @@
For details see: Documentation/admin-guide/hw-vuln/mds.rst For details see: Documentation/admin-guide/hw-vuln/mds.rst
mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
Amount of memory to be used when the kernel is not able Amount of memory to be used in cases as follows:
to see the whole system memory or for test.
1 for test;
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.
[X86] Work as limiting max address. Use together [X86] Work as limiting max address. Use together
with memmap= to avoid physical address space collisions. with memmap= to avoid physical address space collisions.
Without memmap= PCI devices could be placed at addresses Without memmap= PCI devices could be placed at addresses
belonging to unused RAM. belonging to unused RAM.
Note that this only takes effects during boot time since
in above case 3, memory may need be hot added after boot
if system memory of hypervisor is not sufficient.
mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
memory. memory.
......
...@@ -105,7 +105,13 @@ static struct resource *register_memory_resource(u64 start, u64 size) ...@@ -105,7 +105,13 @@ static struct resource *register_memory_resource(u64 start, u64 size)
unsigned long flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY; unsigned long flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
char *resource_name = "System RAM"; char *resource_name = "System RAM";
if (start + size > max_mem_size) /*
* Make sure value parsed from 'mem=' only restricts memory adding
* while booting, so that memory hotplug won't be impacted. Please
* refer to document of 'mem=' in kernel-parameters.txt for more
* details.
*/
if (start + size > max_mem_size && system_state < SYSTEM_RUNNING)
return ERR_PTR(-E2BIG); return ERR_PTR(-E2BIG);
/* /*
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment