[PATCH v2 0/4] arch, mm: improve robustness of direct map manipulation

Mike Rapoport
2020-10-29T16:19:54Z

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, it is updated to make direct map accesses there more
explicit.

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

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

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

Mike Rapoport (4):
mm: introduce debug_pagealloc_map_pages() helper
PM: hibernate: make direct map manipulations more explicit
arch, mm: restore dependency of __kernel_map_pages() of 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 | 35 +++++++++++++----------------
include/linux/set_memory.h | 5 +++++
kernel/power/snapshot.c | 30 +++++++++++++++++++++++--
mm/memory_hotplug.c | 3 +--
mm/page_alloc.c | 6 ++---
mm/slab.c | 8 +++----
20 files changed, 103 insertions(+), 58 deletions(-)