linux-stable

mirror of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git synced 2024-11-01 17:08:10 +00:00

No description

Find a file

David Hildenbrand 25bc5b0de9 proc/vmcore: don't fake reading zeroes on surprise vmcore_cb unregistration In commit `cc5f2704c9` ("proc/vmcore: convert oldmem_pfn_is_ram callback to more generic vmcore callbacks"), we added detection of surprise vmcore_cb unregistration after the vmcore was already opened. Once detected, we warn the user and simulate reading zeroes from that point on when accessing the vmcore. The basic reason was that unexpected unregistration, for example, by manually unbinding a driver from a device after opening the vmcore, is not supported and could result in reading oldmem the vmcore_cb would have actually prohibited while registered. However, something like that can similarly be trigger by a user that's really looking for trouble simply by unbinding the relevant driver before opening the vmcore -- or by disallowing loading the driver in the first place. So it's actually of limited help. Currently, unregistration can only be triggered via virtio-mem when manually unbinding the driver from the device inside the VM; there is no way to trigger it from the hypervisor, as hypervisors don't allow for unplugging virtio-mem devices -- ripping out system RAM from a VM without coordination with the guest is usually not a good idea. The important part is that unbinding the driver and unregistering the vmcore_cb while concurrently reading the vmcore won't crash the system, and that is handled by the rwsem. To make the mechanism more future proof, let's remove the "read zero" part, but leave the warning in place. For example, we could have a future driver (like virtio-balloon) that will contact the hypervisor to figure out if we already populated a page for a given PFN. Hotunplugging such a device and consequently unregistering the vmcore_cb could be triggered from the hypervisor without harming the system even while kdump is running. In that case, we don't want to silently end up with a vmcore that contains wrong data, because the user inside the VM might be unaware of the hypervisor action and might easily miss the warning in the log. Link: https://lkml.kernel.org/r/20211111192243.22002-1-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Baoquan He <bhe@redhat.com> Cc: Dave Young <dyoung@redhat.com> Cc: Vivek Goyal <vgoyal@redhat.com> Cc: Philipp Rudo <prudo@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>		2022-01-20 08:52:52 +02:00
arch	mm: percpu: add generic pcpu_populate_pte() function	2022-01-20 08:52:52 +02:00
block
certs
crypto
Documentation
drivers	mm: percpu: add generic pcpu_populate_pte() function	2022-01-20 08:52:52 +02:00
fs	proc/vmcore: don't fake reading zeroes on surprise vmcore_cb unregistration	2022-01-20 08:52:52 +02:00
include	mm: percpu: add generic pcpu_populate_pte() function	2022-01-20 08:52:52 +02:00
init
ipc
kernel
lib
LICENSES
mm	mm: percpu: add generic pcpu_populate_pte() function	2022-01-20 08:52:52 +02:00
net
samples
scripts
security
sound
tools
usr
virt
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
.mailmap
COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS
Makefile
README

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.