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

Mike Rapoport
2020-11-09T16:48:08Z

Oops, this one has some rebase errors, I'll send v7 soon.
Sorry for the noise.

On Mon, Nov 09, 2020 at 06:24:11PM +0200, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>
>
> 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
>

--
Sincerely yours,
Mike.