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Baoquan He f3cd4c865b mm/memory_hotplug.c: only respect mem= parameter during boot stage 
In commit 357b4da50a ("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 357b4da50a 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: 357b4da50a ("x86: respect memory size limiting via mem= parameter")
Signed-off-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Juergen Gross <jgross@suse.com>
Acked-by: Michal 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.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-07 10:43:40 -07:00
arch userfaultfd: wp: add pmd_swp_*uffd_wp() helpers 2020-04-07 10:43:39 -07:00
block SCSI misc on 20200402 2020-04-02 17:03:53 -07:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2020-04-01 14:47:40 -07:00
Documentation mm/memory_hotplug.c: only respect mem= parameter during boot stage 2020-04-07 10:43:40 -07:00
drivers drivers/base/memory.c: drop pages_correctly_probed() 2020-04-07 10:43:40 -07:00
fs userfaultfd: wp: declare _UFFDIO_WRITEPROTECT conditionally 2020-04-07 10:43:40 -07:00
include drivers/base/memory.c: drop section_count 2020-04-07 10:43:40 -07:00
init userfaultfd: wp: add WP pagetable tracking to x86 2020-04-07 10:43:39 -07:00
ipc Revert "ipc,sem: remove uneeded sem_undo_list lock usage in exit_sem()" 2020-02-21 11:22:15 -08:00
kernel mm/vma: replace all remaining open encodings with is_vm_hugetlb_page() 2020-04-07 10:43:37 -07:00
lib New tracing features: 2020-04-05 10:36:18 -07:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm mm/memory_hotplug.c: only respect mem= parameter during boot stage 2020-04-07 10:43:40 -07:00
net 9p pull request for inclusion in 5.7 2020-04-06 08:46:59 -07:00
samples SPDX patches for 5.7-rc1. 2020-04-03 13:12:26 -07:00
scripts Char/Misc driver patches for 5.7-rc1 2020-04-03 13:22:40 -07:00
security Keyrings fixes 2020-04-04 12:24:47 -07:00
sound SPDX patches for 5.7-rc1. 2020-04-03 13:12:26 -07:00
tools userfaultfd: selftests: add write-protect test 2020-04-07 10:43:40 -07:00
usr .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
virt KVM: Pass kvm_init()'s opaque param to additional arch funcs 2020-03-31 10:48:03 -04:00
.clang-format clang-format: Update with the latest for_each macro list 2020-03-06 21:50:05 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
.mailmap media updates for v5.7-rc1 2020-03-30 13:42:05 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Hand MIPS over to Thomas 2020-02-24 22:43:18 -08:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS powerpc updates for 5.7 2020-04-05 11:12:59 -07:00
Makefile Kbuild updates for v5.7 2020-03-31 16:03:39 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.