Re: [PATCH v4 3/4] arch, mm: restore dependency of __kernel_map_pages() of DEBUG_PAGEALLOC

Vlastimil Babka
2020-11-04T18:02:42Z

On 11/3/20 5:20 PM, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>

Subject should have "on DEBUG_PAGEALLOC" ?

> The design of DEBUG_PAGEALLOC presumes that __kernel_map_pages() must never
> fail. With this assumption is wouldn't be safe to allow general usage of
> this function.
>
> Moreover, some architectures that implement __kernel_map_pages() have this
> function guarded by #ifdef DEBUG_PAGEALLOC and some refuse to map/unmap
> pages when page allocation debugging is disabled at runtime.
>
> As all the users of __kernel_map_pages() were converted to use
> debug_pagealloc_map_pages() it is safe to make it available only when
> DEBUG_PAGEALLOC is set.
>
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> Acked-by: David Hildenbrand <david@redhat.com>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
> arch/Kconfig | 3 +++
> arch/arm64/Kconfig | 4 +---
> arch/arm64/mm/pageattr.c | 8 ++++++--
> arch/powerpc/Kconfig | 5 +----
> arch/riscv/Kconfig | 4 +---
> arch/riscv/include/asm/pgtable.h | 2 --
> arch/riscv/mm/pageattr.c | 2 ++
> arch/s390/Kconfig | 4 +---
> arch/sparc/Kconfig | 4 +---
> arch/x86/Kconfig | 4 +---
> arch/x86/mm/pat/set_memory.c | 2 ++
> include/linux/mm.h | 10 +++++++---
> 12 files changed, 26 insertions(+), 26 deletions(-)
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 56b6ccc0e32d..56d4752b6db6 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -1028,6 +1028,9 @@ config HAVE_STATIC_CALL_INLINE
> bool
> depends on HAVE_STATIC_CALL
>
> +config ARCH_SUPPORTS_DEBUG_PAGEALLOC
> + bool
> +
> source "kernel/gcov/Kconfig"
>
> source "scripts/gcc-plugins/Kconfig"
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 1d466addb078..a932810cfd90 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -71,6 +71,7 @@ config ARM64
> select ARCH_USE_QUEUED_RWLOCKS
> select ARCH_USE_QUEUED_SPINLOCKS
> select ARCH_USE_SYM_ANNOTATIONS
> + select ARCH_SUPPORTS_DEBUG_PAGEALLOC
> select ARCH_SUPPORTS_MEMORY_FAILURE
> select ARCH_SUPPORTS_SHADOW_CALL_STACK if CC_HAVE_SHADOW_CALL_STACK
> select ARCH_SUPPORTS_ATOMIC_RMW
> @@ -1025,9 +1026,6 @@ config HOLES_IN_ZONE
>
> source "kernel/Kconfig.hz"
>
> -config ARCH_SUPPORTS_DEBUG_PAGEALLOC
> - def_bool y
> -
> config ARCH_SPARSEMEM_ENABLE
> def_bool y
> select SPARSEMEM_VMEMMAP_ENABLE
> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> index 1b94f5b82654..439325532be1 100644
> --- a/arch/arm64/mm/pageattr.c
> +++ b/arch/arm64/mm/pageattr.c
> @@ -155,7 +155,7 @@ int set_direct_map_invalid_noflush(struct page *page)
> .clear_mask = __pgprot(PTE_VALID),
> };
>
> - if (!rodata_full)
> + if (!debug_pagealloc_enabled() && !rodata_full)
> return 0;
>
> return apply_to_page_range(&init_mm,
> @@ -170,7 +170,7 @@ int set_direct_map_default_noflush(struct page *page)
> .clear_mask = __pgprot(PTE_RDONLY),
> };
>
> - if (!rodata_full)
> + if (!debug_pagealloc_enabled() && !rodata_full)
> return 0;
>
> return apply_to_page_range(&init_mm,

I don't understand these two hunks. Previous patch calls this for hibernation
when CONFIG_ARCH_HAS_SET_DIRECT_MAP, which is true for arm64. Why suddenly this
starts to depend on debug_pagealloc_enabled()?