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

From: Mike Rapoport <[email-masked]>
Date: Mon, 9 Nov 2020 18:47:52 +0200

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 <[email-masked]>
> 
> 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/[email-masked]
> 
> 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/[email-masked]
> 
> 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/[email-masked]
> 
> v3 changes:
> * update arm64 changes to avoid regression, per Rick's comments
> * fix bisectability
> https://lore.kernel.org/lkml/[email-masked]
> 
> 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/[email-masked]
> 
> v1:
> https://lore.kernel.org/lkml/[email-masked]
> 
> 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.