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

[Vlastimil Babka <vbabka@suse.cz>]

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()?

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