Looking for places where the kernel might unconditionally read PageOffline() pages, I stumbled over /proc/kcore; turns out /proc/kcore needs some more love to not touch some other pages we really don't want to read -- i.e., hwpoisoned ones. Examples for PageOffline() pages are pages inflated in a balloon, memory unplugged via virtio-mem, and partially-present sections in memory added by the Hyper-V balloon. When reading pages inflated in a balloon, we essentially produce unnecessary load in the hypervisor; holes in partially present sections in case of Hyper-V are not accessible and already were a problem for /proc/vmcore, fixed in makedumpfile by detecting PageOffline() pages. In the future, virtio-mem might disallow reading unplugged memory -- marked as PageOffline() -- in some environments, resulting in undefined behavior when accessed; therefore, I'm trying to identify and rework all these (corner) cases. With this series, there is really only access via /dev/mem, /proc/vmcore and kdb left after I ripped out /dev/kmem. kdb is an advanced corner-case use case -- we won't care for now if someone explicitly tries to do nasty things by reading from/writing to physical addresses we better not touch. /dev/mem is a use case we won't support for virtio-mem, at least for now, so we'll simply disallow mapping any virtio-mem memory via /dev/mem next. /proc/vmcore is really only a problem when dumping the old kernel via something that's not makedumpfile (read: basically never), however, we'll try sanitizing that as well in the second kernel in the future. Tested via kcore_dump: https://github.com/schlafwandler/kcore_dump v2 -> v3: - "mm: introduce page_offline_(begin|end|freeze|thaw) to synchronize setting PageOffline()" -- Rephrased a comment as suggested by Mike - Collected acks and rbs v1 -> v2: - Dropped "mm: rename and move page_is_poisoned()" - "fs/proc/kcore: don't read offline sections, logically offline pages ..." -- Add is_page_hwpoison() in page-flags.h along with a comment - "mm: introduce page_offline_(begin|end|freeze|thaw) to ..." -- s/unfreeze/thaw/ -- Add a comment to PageOffline documentation in page-flags.h - "virtio-mem: use page_offline_(start|end) when setting PageOffline()" -- Extend patch description - "fs/proc/kcore: use page_offline_(freeze|thaw)" -- Simplify freeze/thaw logic - Collected acks/rbs Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx> Cc: Jason Wang <jasowang@xxxxxxxxxx> Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx> Cc: Mike Rapoport <rppt@xxxxxxxxxx> Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx> Cc: Oscar Salvador <osalvador@xxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Roman Gushchin <guro@xxxxxx> Cc: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx> Cc: Steven Price <steven.price@xxxxxxx> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Cc: Aili Yao <yaoaili@xxxxxxxxxxxx> Cc: Jiri Bohac <jbohac@xxxxxxx> Cc: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx> Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx> Cc: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx> Cc: Wei Liu <wei.liu@xxxxxxxxxx> Cc: Naoya Horiguchi <naoya.horiguchi@xxxxxxx> Cc: linux-hyperv@xxxxxxxxxxxxxxx Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx Cc: linux-fsdevel@xxxxxxxxxxxxxxx Cc: linux-mm@xxxxxxxxx David Hildenbrand (6): fs/proc/kcore: drop KCORE_REMAP and KCORE_OTHER fs/proc/kcore: pfn_is_ram check only applies to KCORE_RAM fs/proc/kcore: don't read offline sections, logically offline pages and hwpoisoned pages mm: introduce page_offline_(begin|end|freeze|thaw) to synchronize setting PageOffline() virtio-mem: use page_offline_(start|end) when setting PageOffline() fs/proc/kcore: use page_offline_(freeze|thaw) drivers/virtio/virtio_mem.c | 2 ++ fs/proc/kcore.c | 67 ++++++++++++++++++++++++++++++------- include/linux/kcore.h | 3 -- include/linux/page-flags.h | 22 ++++++++++++ mm/util.c | 40 ++++++++++++++++++++++ 5 files changed, 118 insertions(+), 16 deletions(-) base-commit: 6efb943b8616ec53a5e444193dccf1af9ad627b5 -- 2.31.1
