[PATCH v6 0/4] arch, mm: improve robustness of direct map manipulation

Mike Rapoport
2020-11-09T16:24:33Z

Hi,

During recent discussion about KVM protected memory, David raised a concern
about usage of __kernel_map_pages() outside of DEBUG_PAGEALLOC scope [1].

Indeed, for architectures that define CONFIG_ARCH_HAS_SET_DIRECT_MAP it is
possible that __kernel_map_pages() would fail, but since this function is
void, the failure will go unnoticed.

Moreover, there's lack of consistency of __kernel_map_pages() semantics
across architectures as some guard this function with
#ifdef DEBUG_PAGEALLOC, some refuse to update the direct map if page
allocation debugging is disabled at run time and some allow modifying the
direct map regardless of DEBUG_PAGEALLOC settings.

This set straightens this out by restoring dependency of
__kernel_map_pages() on DEBUG_PAGEALLOC and updating the call sites
accordingly.

Since currently the only user of __kernel_map_pages() outside
DEBUG_PAGEALLOC is hibernation, it is updated to make direct map accesses
there more explicit.

[1] https://lore.kernel.org/lkml/2759b4bf-e1e3-d006-7d86-78a40348269d@redhat.com

v6 changes:
* revert slab changes to avoid redundant check of static key

v5 changes:
* use pairs of _map()/_unmap() functions instead of _map(..., int enable) as
Vlastimil suggested
https://lore.kernel.org/lkml/20201108065758.1815-1-rppt@kernel.org

v4 changes:
* s/WARN_ON/pr_warn_once/ per David and Kirill
* rebase on v5.10-rc2
* add Acked/Reviewed tags
https://lore.kernel.org/lkml/20201103162057.22916-1-rppt@kernel.org

v3 changes:
* update arm64 changes to avoid regression, per Rick's comments
* fix bisectability
https://lore.kernel.org/lkml/20201101170815.9795-1-rppt@kernel.org

v2 changes:
* Rephrase patch 2 changelog to better describe the change intentions and
implications
* Move removal of kernel_map_pages() from patch 1 to patch 2, per David
https://lore.kernel.org/lkml/20201029161902.19272-1-rppt@kernel.org

v1:
https://lore.kernel.org/lkml/20201025101555.3057-1-rppt@kernel.org

Mike Rapoport (4):
mm: introduce debug_pagealloc_{map,unmap}_pages() helpers
PM: hibernate: make direct map manipulations more explicit
arch, mm: restore dependency of __kernel_map_pages() on DEBUG_PAGEALLOC
arch, mm: make kernel_page_present() always available

arch/Kconfig | 3 +++
arch/arm64/Kconfig | 4 +--
arch/arm64/include/asm/cacheflush.h | 1 +
arch/arm64/mm/pageattr.c | 6 +++--
arch/powerpc/Kconfig | 5 +---
arch/riscv/Kconfig | 4 +--
arch/riscv/include/asm/pgtable.h | 2 --
arch/riscv/include/asm/set_memory.h | 1 +
arch/riscv/mm/pageattr.c | 31 ++++++++++++++++++++++
arch/s390/Kconfig | 4 +--
arch/sparc/Kconfig | 4 +--
arch/x86/Kconfig | 4 +--
arch/x86/include/asm/set_memory.h | 1 +
arch/x86/mm/pat/set_memory.c | 4 +--
include/linux/mm.h | 40 ++++++++++++++---------------
include/linux/set_memory.h | 5 ++++
kernel/power/snapshot.c | 38 +++++++++++++++++++++++++--
mm/memory_hotplug.c | 3 +--
mm/page_alloc.c | 6 ++---
19 files changed, 113 insertions(+), 53 deletions(-)

--
2.28.0