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

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On 11/3/20 5:20 PM, Mike Rapoport wrote:
From: Mike Rapoport <rppt@xxxxxxxxxxxxx>

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@xxxxxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
  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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