linux.git/kernel/ksysfs.c, branch v6.6.131

crash: hotplug support for kexec_load()

2023-08-24T23:25:14+00:00

The hotplug support for kexec_load() requires changes to the userspace
kexec-tools and a little extra help from the kernel.

Given a kdump capture kernel loaded via kexec_load(), and a subsequent
hotplug event, the crash hotplug handler finds the elfcorehdr and rewrites
it to reflect the hotplug change.  That is the desired outcome, however,
at kernel panic time, the purgatory integrity check fails (because the
elfcorehdr changed), and the capture kernel does not boot and no vmcore is
generated.

Therefore, the userspace kexec-tools/kexec must indicate to the kernel
that the elfcorehdr can be modified (because the kexec excluded the
elfcorehdr from the digest, and sized the elfcorehdr memory buffer
appropriately).

To facilitate hotplug support with kexec_load():
 - a new kexec flag KEXEC_UPATE_ELFCOREHDR indicates that it is
   safe for the kernel to modify the kexec_load()'d elfcorehdr
 - the /sys/kernel/crash_elfcorehdr_size node communicates the
   preferred size of the elfcorehdr memory buffer
 - The sysfs crash_hotplug nodes (ie.
   /sys/devices/system/[cpu|memory]/crash_hotplug) dynamically
   take into account kexec_file_load() vs kexec_load() and
   KEXEC_UPDATE_ELFCOREHDR.
   This is critical so that the udev rule processing of crash_hotplug
   is all that is needed to determine if the userspace unload-then-load
   of the kdump image is to be skipped, or not. The proposed udev
   rule change looks like:
   # The kernel updates the crash elfcorehdr for CPU and memory changes
   SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end"
   SUBSYSTEM=="memory", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end"

The table below indicates the behavior of kexec_load()'d kdump image
updates (with the new udev crash_hotplug rule in place):

 Kernel |Kexec
 -------+-----+----
 Old    |Old  |New
        |  a  | a
 -------+-----+----
 New    |  a  | b
 -------+-----+----

where kexec 'old' and 'new' delineate kexec-tools has the needed
modifications for the crash hotplug feature, and kernel 'old' and 'new'
delineate the kernel supports this crash hotplug feature.

Behavior 'a' indicates the unload-then-reload of the entire kdump image. 
For the kexec 'old' column, the unload-then-reload occurs due to the
missing flag KEXEC_UPDATE_ELFCOREHDR.  An 'old' kernel (with 'new' kexec)
does not present the crash_hotplug sysfs node, which leads to the
unload-then-reload of the kdump image.

Behavior 'b' indicates the desired optimized behavior of the kernel
directly modifying the elfcorehdr and avoiding the unload-then-reload of
the kdump image.

If the udev rule is not updated with crash_hotplug node check, then no
matter any combination of kernel or kexec is new or old, the kdump image
continues to be unload-then-reload on hotplug changes.

To fully support crash hotplug feature, there needs to be a rollout of
kernel, kexec-tools and udev rule changes.  However, the order of the
rollout of these pieces does not matter; kexec_load()'d kdump images still
function for hotplug as-is.

Link: https://lkml.kernel.org/r/20230814214446.6659-7-eric.devolder@oracle.com
Signed-off-by: Eric DeVolder 
Suggested-by: Hari Bathini 
Acked-by: Hari Bathini 
Acked-by: Baoquan He 
Cc: Akhil Raj 
Cc: Bjorn Helgaas 
Cc: Borislav Petkov (AMD) 
Cc: Boris Ostrovsky 
Cc: Dave Hansen 
Cc: Dave Young 
Cc: David Hildenbrand 
Cc: Eric W. Biederman 
Cc: Greg Kroah-Hartman 
Cc: "H. Peter Anvin" 
Cc: Ingo Molnar 
Cc: Jonathan Corbet 
Cc: Konrad Rzeszutek Wilk 
Cc: Mimi Zohar 
Cc: Naveen N. Rao 
Cc: Oscar Salvador 
Cc: "Rafael J. Wysocki" 
Cc: Sean Christopherson 
Cc: Sourabh Jain 
Cc: Takashi Iwai 
Cc: Thomas Gleixner 
Cc: Thomas Weißschuh 
Cc: Valentin Schneider 
Cc: Vivek Goyal 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton

kernel/ksysfs.c: use sysfs_emit for sysfs show handlers

2023-03-24T16:09:14+00:00

sysfs_emit() is the recommended way to format strings for sysfs as per
Documentation/filesystems/sysfs.rst.

Signed-off-by: Thomas Weißschuh 
Link: https://lore.kernel.org/r/20230324-ksysfs-sysfs_emit-v1-1-67c03cddc8a6@weissschuh.net
Signed-off-by: Greg Kroah-Hartman

kernels/ksysfs.c: export kernel address bits

2023-01-20T13:30:45+00:00

This can be used by userspace to determine the address size of the
running kernel.
It frees userspace from having to interpret this information from the
UTS machine field.

Userspace implementation:
https://github.com/util-linux/util-linux/pull/1966

Signed-off-by: Thomas Weißschuh 
Link: https://lore.kernel.org/r/20221221-address-bits-v1-1-8446b13244ac@weissschuh.net
Signed-off-by: Greg Kroah-Hartman

kernel/ksysfs.c: export kernel cpu byteorder

2022-11-10T18:07:31+00:00

Certain files in procfs are formatted in byteorder-dependent formats.
For example the IP addresses in /proc/net/udp.

When using emulation like qemu-user, applications are not guaranteed to
be using the same byteorder as the kernel.
Therefore the kernel needs to provide a way for applications to discover
the byteorder used in API-filesystems.
Using systemcalls is not enough because these are intercepted and
translated by the emulation.

Also this makes it easier for non-compiled applications like
shellscripts to discover the byteorder.

Signed-off-by: Thomas Weißschuh 
Link: https://lore.kernel.org/r/20221103152407.3348-1-linux@weissschuh.net
Signed-off-by: Greg Kroah-Hartman

kexec: turn all kexec_mutex acquisitions into trylocks

2022-09-12T04:55:06+00:00

Patch series "kexec, panic: Making crash_kexec() NMI safe", v4.


This patch (of 2):

Most acquistions of kexec_mutex are done via mutex_trylock() - those were
a direct "translation" from:

  8c5a1cf0ad3a ("kexec: use a mutex for locking rather than xchg()")

there have however been two additions since then that use mutex_lock():
crash_get_memory_size() and crash_shrink_memory().

A later commit will replace said mutex with an atomic variable, and
locking operations will become atomic_cmpxchg().  Rather than having those
mutex_lock() become while (atomic_cmpxchg(&lock, 0, 1)), turn them into
trylocks that can return -EBUSY on acquisition failure.

This does halve the printable size of the crash kernel, but that's still
neighbouring 2G for 32bit kernels which should be ample enough.

Link: https://lkml.kernel.org/r/20220630223258.4144112-1-vschneid@redhat.com
Link: https://lkml.kernel.org/r/20220630223258.4144112-2-vschneid@redhat.com
Signed-off-by: Valentin Schneider 
Cc: Arnd Bergmann 
Cc: "Eric W . Biederman" 
Cc: Juri Lelli 
Cc: Luis Claudio R. Goncalves 
Cc: Miaohe Lin 
Cc: Petr Mladek 
Cc: Sebastian Andrzej Siewior 
Cc: Thomas Gleixner 
Cc: Baoquan He 
Signed-off-by: Andrew Morton

kernel/ksysfs.c: use helper macro __ATTR_RW

2022-03-24T02:00:33+00:00

Use helper macro __ATTR_RW to define kobj_attribute to make code more
clear.  Minor readability improvement.

Link: https://lkml.kernel.org/r/20220222112034.48298-1-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin 
Cc: Greg Kroah-Hartman 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 170

2019-05-30T18:26:39+00:00

Based on 1 normalized pattern(s):

  this file is release under the gplv2

extracted by the scancode license scanner the SPDX license identifier

  GPL-2.0-only

has been chosen to replace the boilerplate/reference in 1 file(s).

Signed-off-by: Thomas Gleixner 
Reviewed-by: Richard Fontana 
Reviewed-by: Kate Stewart 
Reviewed-by: Armijn Hemel 
Reviewed-by: Allison Randal 
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190527070034.216732358@linutronix.de
Signed-off-by: Greg Kroah-Hartman

kexec: move vmcoreinfo out of the kernel's .bss section

2017-07-12T23:25:59+00:00

As Eric said,
 "what we need to do is move the variable vmcoreinfo_note out of the
  kernel's .bss section. And modify the code to regenerate and keep this
  information in something like the control page.

  Definitely something like this needs a page all to itself, and ideally
  far away from any other kernel data structures. I clearly was not
  watching closely the data someone decided to keep this silly thing in
  the kernel's .bss section."

This patch allocates extra pages for these vmcoreinfo_XXX variables, one
advantage is that it enhances some safety of vmcoreinfo, because
vmcoreinfo now is kept far away from other kernel data structures.

Link: http://lkml.kernel.org/r/1493281021-20737-1-git-send-email-xlpang@redhat.com
Signed-off-by: Xunlei Pang 
Tested-by: Michael Holzheu 
Reviewed-by: Juergen Gross 
Suggested-by: Eric Biederman 
Cc: Benjamin Herrenschmidt 
Cc: Dave Young 
Cc: Hari Bathini 
Cc: Mahesh Salgaonkar 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

kernel/ksysfs.c: constify attribute_group structures.

2017-07-10T23:32:34+00:00

attribute_groups are not supposed to change at runtime.  All functions
working with attribute_groups provided by  work with
const attribute_group.  So mark the non-const structs as const.

File size before:
   text	   data	    bss	    dec	    hex	filename
   1120	    544	     16	   1680	    690	kernel/ksysfs.o

File size After adding 'const':
   text	   data	    bss	    dec	    hex	filename
   1160	    480	     16	   1656	    678	kernel/ksysfs.o

Link: http://lkml.kernel.org/r/aa224b3cc923fdbb3edd0c41b2c639c85408c9e8.1498737347.git.arvind.yadav.cs@gmail.com
Signed-off-by: Arvind Yadav 
Acked-by: Kees Cook 
Cc: Russell King 
Cc: Dave Young 
Cc: Hari Bathini 
Cc: Petr Tesarik 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

crash: move crashkernel parsing and vmcore related code under CONFIG_CRASH_CORE

2017-05-09T00:15:11+00:00

Patch series "kexec/fadump: remove dependency with CONFIG_KEXEC and
reuse crashkernel parameter for fadump", v4.

Traditionally, kdump is used to save vmcore in case of a crash.  Some
architectures like powerpc can save vmcore using architecture specific
support instead of kexec/kdump mechanism.  Such architecture specific
support also needs to reserve memory, to be used by dump capture kernel.
crashkernel parameter can be a reused, for memory reservation, by such
architecture specific infrastructure.

This patchset removes dependency with CONFIG_KEXEC for crashkernel
parameter and vmcoreinfo related code as it can be reused without kexec
support.  Also, crashkernel parameter is reused instead of
fadump_reserve_mem to reserve memory for fadump.

The first patch moves crashkernel parameter parsing and vmcoreinfo
related code under CONFIG_CRASH_CORE instead of CONFIG_KEXEC_CORE.  The
second patch reuses the definitions of append_elf_note() & final_note()
functions under CONFIG_CRASH_CORE in IA64 arch code.  The third patch
removes dependency on CONFIG_KEXEC for firmware-assisted dump (fadump)
in powerpc.  The next patch reuses crashkernel parameter for reserving
memory for fadump, instead of the fadump_reserve_mem parameter.  This
has the advantage of using all syntaxes crashkernel parameter supports,
for fadump as well.  The last patch updates fadump kernel documentation
about use of crashkernel parameter.

This patch (of 5):

Traditionally, kdump is used to save vmcore in case of a crash.  Some
architectures like powerpc can save vmcore using architecture specific
support instead of kexec/kdump mechanism.  Such architecture specific
support also needs to reserve memory, to be used by dump capture kernel.
crashkernel parameter can be a reused, for memory reservation, by such
architecture specific infrastructure.

But currently, code related to vmcoreinfo and parsing of crashkernel
parameter is built under CONFIG_KEXEC_CORE.  This patch introduces
CONFIG_CRASH_CORE and moves the above mentioned code under this config,
allowing code reuse without dependency on CONFIG_KEXEC.  There is no
functional change with this patch.

Link: http://lkml.kernel.org/r/149035338104.6881.4550894432615189948.stgit@hbathini.in.ibm.com
Signed-off-by: Hari Bathini 
Acked-by: Dave Young 
Cc: Fenghua Yu 
Cc: Tony Luck 
Cc: Eric Biederman 
Cc: Mahesh Salgaonkar 
Cc: Vivek Goyal 
Cc: Michael Ellerman 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds