[PATCH v4 0/4] arch, mm: improve robustness of direct map manipulation

[PATCH v4 0/4] arch, mm: improve robustness of direct map manipulation

[Mike Rapoport]

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

v4 changes:
* s/WARN_ON/pr_warn_once/ per David and Kirill
* rebase on v5.10-rc2
* add Acked/Reviewed tags

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_pages() helper
  PM: hibernate: make direct map manipulations more explicit
  arch, mm: restore dependency of __kernel_map_pages() of 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                  | 35 +++++++++++++----------------
 include/linux/set_memory.h          |  5 +++++
 kernel/power/snapshot.c             | 30 +++++++++++++++++++++++--
 mm/memory_hotplug.c                 |  3 +--
 mm/page_alloc.c                     |  6 ++---
 mm/slab.c                           |  8 +++----
 20 files changed, 103 insertions(+), 58 deletions(-)

-- 
2.28.0

*** BLURB HERE ***

Mike Rapoport (4):
  mm: introduce debug_pagealloc_map_pages() helper
  PM: hibernate: make direct map manipulations more explicit
  arch, mm: restore dependency of __kernel_map_pages() of
    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                  | 35 +++++++++++++----------------
 include/linux/set_memory.h          |  5 +++++
 kernel/power/snapshot.c             | 32 ++++++++++++++++++++++++--
 mm/memory_hotplug.c                 |  3 +--
 mm/page_alloc.c                     |  6 ++---
 mm/slab.c                           |  8 +++----
 20 files changed, 105 insertions(+), 58 deletions(-)


base-commit: 3cea11cd5e3b00d91caf0b4730194039b45c5891
-- 
2.28.0


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[PATCH v4 1/4] mm: introduce debug_pagealloc_map_pages() helper

[Mike Rapoport]

From: Mike Rapoport <rppt@linux.ibm.com>

When CONFIG_DEBUG_PAGEALLOC is enabled, it unmaps pages from the kernel
direct mapping after free_pages(). The pages than need to be mapped back
before they could be used. Theese mapping operations use
__kernel_map_pages() guarded with with debug_pagealloc_enabled().

The only place that calls __kernel_map_pages() without checking whether
DEBUG_PAGEALLOC is enabled is the hibernation code that presumes
availability of this function when ARCH_HAS_SET_DIRECT_MAP is set.
Still, on arm64, __kernel_map_pages() will bail out when DEBUG_PAGEALLOC is
not enabled but set_direct_map_invalid_noflush() may render some pages not
present in the direct map and hibernation code won't be able to save such
pages.

To make page allocation debugging and hibernation interaction more robust,
the dependency on DEBUG_PAGEALLOC or ARCH_HAS_SET_DIRECT_MAP has to be made
more explicit.

Start with combining the guard condition and the call to
__kernel_map_pages() into a single debug_pagealloc_map_pages() function to
emphasize that __kernel_map_pages() should not be called without
DEBUG_PAGEALLOC and use this new function to map/unmap pages when page
allocation debug is enabled.

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 include/linux/mm.h  | 10 ++++++++++
 mm/memory_hotplug.c |  3 +--
 mm/page_alloc.c     |  6 ++----
 mm/slab.c           |  8 +++-----
 4 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ef360fe70aaf..1fc0609056dc 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2936,12 +2936,22 @@ kernel_map_pages(struct page *page, int numpages, int enable)
 {
 	__kernel_map_pages(page, numpages, enable);
 }
+
+static inline void debug_pagealloc_map_pages(struct page *page,
+					     int numpages, int enable)
+{
+	if (debug_pagealloc_enabled_static())
+		__kernel_map_pages(page, numpages, enable);
+}
+
 #ifdef CONFIG_HIBERNATION
 extern bool kernel_page_present(struct page *page);
 #endif	/* CONFIG_HIBERNATION */
 #else	/* CONFIG_DEBUG_PAGEALLOC || CONFIG_ARCH_HAS_SET_DIRECT_MAP */
 static inline void
 kernel_map_pages(struct page *page, int numpages, int enable) {}
+static inline void debug_pagealloc_map_pages(struct page *page,
+					     int numpages, int enable) {}
 #ifdef CONFIG_HIBERNATION
 static inline bool kernel_page_present(struct page *page) { return true; }
 #endif	/* CONFIG_HIBERNATION */
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index b44d4c7ba73b..e2b6043a4428 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -614,8 +614,7 @@ void generic_online_page(struct page *page, unsigned int order)
 	 * so we should map it first. This is better than introducing a special
 	 * case in page freeing fast path.
 	 */
-	if (debug_pagealloc_enabled_static())
-		kernel_map_pages(page, 1 << order, 1);
+	debug_pagealloc_map_pages(page, 1 << order, 1);
 	__free_pages_core(page, order);
 	totalram_pages_add(1UL << order);
 #ifdef CONFIG_HIGHMEM
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 23f5066bd4a5..9a66a1ff9193 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1272,8 +1272,7 @@ static __always_inline bool free_pages_prepare(struct page *page,
 	 */
 	arch_free_page(page, order);
 
-	if (debug_pagealloc_enabled_static())
-		kernel_map_pages(page, 1 << order, 0);
+	debug_pagealloc_map_pages(page, 1 << order, 0);
 
 	kasan_free_nondeferred_pages(page, order);
 
@@ -2270,8 +2269,7 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
 	set_page_refcounted(page);
 
 	arch_alloc_page(page, order);
-	if (debug_pagealloc_enabled_static())
-		kernel_map_pages(page, 1 << order, 1);
+	debug_pagealloc_map_pages(page, 1 << order, 1);
 	kasan_alloc_pages(page, order);
 	kernel_poison_pages(page, 1 << order, 1);
 	set_page_owner(page, order, gfp_flags);
diff --git a/mm/slab.c b/mm/slab.c
index b1113561b98b..340db0ce74c4 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1431,10 +1431,8 @@ static bool is_debug_pagealloc_cache(struct kmem_cache *cachep)
 #ifdef CONFIG_DEBUG_PAGEALLOC
 static void slab_kernel_map(struct kmem_cache *cachep, void *objp, int map)
 {
-	if (!is_debug_pagealloc_cache(cachep))
-		return;
-
-	kernel_map_pages(virt_to_page(objp), cachep->size / PAGE_SIZE, map);
+	debug_pagealloc_map_pages(virt_to_page(objp),
+				  cachep->size / PAGE_SIZE, map);
 }
 
 #else
@@ -2062,7 +2060,7 @@ int __kmem_cache_create(struct kmem_cache *cachep, slab_flags_t flags)
 
 #if DEBUG
 	/*
-	 * If we're going to use the generic kernel_map_pages()
+	 * If we're going to use the generic debug_pagealloc_map_pages()
 	 * poisoning, then it's going to smash the contents of
 	 * the redzone and userword anyhow, so switch them off.
 	 */
-- 
2.28.0


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Re: [PATCH v4 1/4] mm: introduce debug_pagealloc_map_pages() helper

[Vlastimil Babka]

On 11/3/20 5:20 PM, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>
> 
> When CONFIG_DEBUG_PAGEALLOC is enabled, it unmaps pages from the kernel
> direct mapping after free_pages(). The pages than need to be mapped back
> before they could be used. Theese mapping operations use
> __kernel_map_pages() guarded with with debug_pagealloc_enabled().
> 
> The only place that calls __kernel_map_pages() without checking whether
> DEBUG_PAGEALLOC is enabled is the hibernation code that presumes
> availability of this function when ARCH_HAS_SET_DIRECT_MAP is set.
> Still, on arm64, __kernel_map_pages() will bail out when DEBUG_PAGEALLOC is
> not enabled but set_direct_map_invalid_noflush() may render some pages not
> present in the direct map and hibernation code won't be able to save such
> pages.
> 
> To make page allocation debugging and hibernation interaction more robust,
> the dependency on DEBUG_PAGEALLOC or ARCH_HAS_SET_DIRECT_MAP has to be made
> more explicit.
> 
> Start with combining the guard condition and the call to
> __kernel_map_pages() into a single debug_pagealloc_map_pages() function to
> emphasize that __kernel_map_pages() should not be called without
> DEBUG_PAGEALLOC and use this new function to map/unmap pages when page
> allocation debug is enabled.
> 
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> Reviewed-by: David Hildenbrand <david@redhat.com>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

But, the "enable" param is hideous. I would rather have map and unmap variants 
(and just did the same split for page poisoning) and this seems to be a good 
opportunity. If David didn't propose it already, I'm surprised ;)

> ---
>   include/linux/mm.h  | 10 ++++++++++
>   mm/memory_hotplug.c |  3 +--
>   mm/page_alloc.c     |  6 ++----
>   mm/slab.c           |  8 +++-----
>   4 files changed, 16 insertions(+), 11 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index ef360fe70aaf..1fc0609056dc 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2936,12 +2936,22 @@ kernel_map_pages(struct page *page, int numpages, int enable)
>   {
>   	__kernel_map_pages(page, numpages, enable);
>   }
> +
> +static inline void debug_pagealloc_map_pages(struct page *page,
> +					     int numpages, int enable)
> +{
> +	if (debug_pagealloc_enabled_static())
> +		__kernel_map_pages(page, numpages, enable);
> +}
> +
>   #ifdef CONFIG_HIBERNATION
>   extern bool kernel_page_present(struct page *page);
>   #endif	/* CONFIG_HIBERNATION */
>   #else	/* CONFIG_DEBUG_PAGEALLOC || CONFIG_ARCH_HAS_SET_DIRECT_MAP */
>   static inline void
>   kernel_map_pages(struct page *page, int numpages, int enable) {}
> +static inline void debug_pagealloc_map_pages(struct page *page,
> +					     int numpages, int enable) {}
>   #ifdef CONFIG_HIBERNATION
>   static inline bool kernel_page_present(struct page *page) { return true; }
>   #endif	/* CONFIG_HIBERNATION */
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index b44d4c7ba73b..e2b6043a4428 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -614,8 +614,7 @@ void generic_online_page(struct page *page, unsigned int order)
>   	 * so we should map it first. This is better than introducing a special
>   	 * case in page freeing fast path.
>   	 */
> -	if (debug_pagealloc_enabled_static())
> -		kernel_map_pages(page, 1 << order, 1);
> +	debug_pagealloc_map_pages(page, 1 << order, 1);
>   	__free_pages_core(page, order);
>   	totalram_pages_add(1UL << order);
>   #ifdef CONFIG_HIGHMEM
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 23f5066bd4a5..9a66a1ff9193 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1272,8 +1272,7 @@ static __always_inline bool free_pages_prepare(struct page *page,
>   	 */
>   	arch_free_page(page, order);
>   
> -	if (debug_pagealloc_enabled_static())
> -		kernel_map_pages(page, 1 << order, 0);
> +	debug_pagealloc_map_pages(page, 1 << order, 0);
>   
>   	kasan_free_nondeferred_pages(page, order);
>   
> @@ -2270,8 +2269,7 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
>   	set_page_refcounted(page);
>   
>   	arch_alloc_page(page, order);
> -	if (debug_pagealloc_enabled_static())
> -		kernel_map_pages(page, 1 << order, 1);
> +	debug_pagealloc_map_pages(page, 1 << order, 1);
>   	kasan_alloc_pages(page, order);
>   	kernel_poison_pages(page, 1 << order, 1);
>   	set_page_owner(page, order, gfp_flags);
> diff --git a/mm/slab.c b/mm/slab.c
> index b1113561b98b..340db0ce74c4 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -1431,10 +1431,8 @@ static bool is_debug_pagealloc_cache(struct kmem_cache *cachep)
>   #ifdef CONFIG_DEBUG_PAGEALLOC
>   static void slab_kernel_map(struct kmem_cache *cachep, void *objp, int map)
>   {
> -	if (!is_debug_pagealloc_cache(cachep))
> -		return;
> -
> -	kernel_map_pages(virt_to_page(objp), cachep->size / PAGE_SIZE, map);
> +	debug_pagealloc_map_pages(virt_to_page(objp),
> +				  cachep->size / PAGE_SIZE, map);
>   }
>   
>   #else
> @@ -2062,7 +2060,7 @@ int __kmem_cache_create(struct kmem_cache *cachep, slab_flags_t flags)
>   
>   #if DEBUG
>   	/*
> -	 * If we're going to use the generic kernel_map_pages()
> +	 * If we're going to use the generic debug_pagealloc_map_pages()
>   	 * poisoning, then it's going to smash the contents of
>   	 * the redzone and userword anyhow, so switch them off.
>   	 */
> 


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Re: [PATCH v4 1/4] mm: introduce debug_pagealloc_map_pages() helper

[Mike Rapoport]

On Wed, Nov 04, 2020 at 06:35:50PM +0100, Vlastimil Babka wrote:
> On 11/3/20 5:20 PM, Mike Rapoport wrote:
> > From: Mike Rapoport <rppt@linux.ibm.com>
> > 
> > When CONFIG_DEBUG_PAGEALLOC is enabled, it unmaps pages from the kernel
> > direct mapping after free_pages(). The pages than need to be mapped back
> > before they could be used. Theese mapping operations use
> > __kernel_map_pages() guarded with with debug_pagealloc_enabled().
> > 
> > The only place that calls __kernel_map_pages() without checking whether
> > DEBUG_PAGEALLOC is enabled is the hibernation code that presumes
> > availability of this function when ARCH_HAS_SET_DIRECT_MAP is set.
> > Still, on arm64, __kernel_map_pages() will bail out when DEBUG_PAGEALLOC is
> > not enabled but set_direct_map_invalid_noflush() may render some pages not
> > present in the direct map and hibernation code won't be able to save such
> > pages.
> > 
> > To make page allocation debugging and hibernation interaction more robust,
> > the dependency on DEBUG_PAGEALLOC or ARCH_HAS_SET_DIRECT_MAP has to be made
> > more explicit.
> > 
> > Start with combining the guard condition and the call to
> > __kernel_map_pages() into a single debug_pagealloc_map_pages() function to
> > emphasize that __kernel_map_pages() should not be called without
> > DEBUG_PAGEALLOC and use this new function to map/unmap pages when page
> > allocation debug is enabled.
> > 
> > Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> > Reviewed-by: David Hildenbrand <david@redhat.com>
> > Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> 
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
> 
> But, the "enable" param is hideous. I would rather have map and unmap
> variants (and just did the same split for page poisoning) and this seems to
> be a good opportunity. If David didn't propose it already, I'm surprised ;)

I'm ok with map and unmap, and no, David didn't propose it already :)

> > ---
> >   include/linux/mm.h  | 10 ++++++++++
> >   mm/memory_hotplug.c |  3 +--
> >   mm/page_alloc.c     |  6 ++----
> >   mm/slab.c           |  8 +++-----
> >   4 files changed, 16 insertions(+), 11 deletions(-)
> > 
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index ef360fe70aaf..1fc0609056dc 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -2936,12 +2936,22 @@ kernel_map_pages(struct page *page, int numpages, int enable)
> >   {
> >   	__kernel_map_pages(page, numpages, enable);
> >   }
> > +
> > +static inline void debug_pagealloc_map_pages(struct page *page,
> > +					     int numpages, int enable)
> > +{
> > +	if (debug_pagealloc_enabled_static())
> > +		__kernel_map_pages(page, numpages, enable);
> > +}
> > +
> >   #ifdef CONFIG_HIBERNATION
> >   extern bool kernel_page_present(struct page *page);
> >   #endif	/* CONFIG_HIBERNATION */
> >   #else	/* CONFIG_DEBUG_PAGEALLOC || CONFIG_ARCH_HAS_SET_DIRECT_MAP */
> >   static inline void
> >   kernel_map_pages(struct page *page, int numpages, int enable) {}
> > +static inline void debug_pagealloc_map_pages(struct page *page,
> > +					     int numpages, int enable) {}
> >   #ifdef CONFIG_HIBERNATION
> >   static inline bool kernel_page_present(struct page *page) { return true; }
> >   #endif	/* CONFIG_HIBERNATION */
> > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> > index b44d4c7ba73b..e2b6043a4428 100644
> > --- a/mm/memory_hotplug.c
> > +++ b/mm/memory_hotplug.c
> > @@ -614,8 +614,7 @@ void generic_online_page(struct page *page, unsigned int order)
> >   	 * so we should map it first. This is better than introducing a special
> >   	 * case in page freeing fast path.
> >   	 */
> > -	if (debug_pagealloc_enabled_static())
> > -		kernel_map_pages(page, 1 << order, 1);
> > +	debug_pagealloc_map_pages(page, 1 << order, 1);
> >   	__free_pages_core(page, order);
> >   	totalram_pages_add(1UL << order);
> >   #ifdef CONFIG_HIGHMEM
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 23f5066bd4a5..9a66a1ff9193 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -1272,8 +1272,7 @@ static __always_inline bool free_pages_prepare(struct page *page,
> >   	 */
> >   	arch_free_page(page, order);
> > -	if (debug_pagealloc_enabled_static())
> > -		kernel_map_pages(page, 1 << order, 0);
> > +	debug_pagealloc_map_pages(page, 1 << order, 0);
> >   	kasan_free_nondeferred_pages(page, order);
> > @@ -2270,8 +2269,7 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
> >   	set_page_refcounted(page);
> >   	arch_alloc_page(page, order);
> > -	if (debug_pagealloc_enabled_static())
> > -		kernel_map_pages(page, 1 << order, 1);
> > +	debug_pagealloc_map_pages(page, 1 << order, 1);
> >   	kasan_alloc_pages(page, order);
> >   	kernel_poison_pages(page, 1 << order, 1);
> >   	set_page_owner(page, order, gfp_flags);
> > diff --git a/mm/slab.c b/mm/slab.c
> > index b1113561b98b..340db0ce74c4 100644
> > --- a/mm/slab.c
> > +++ b/mm/slab.c
> > @@ -1431,10 +1431,8 @@ static bool is_debug_pagealloc_cache(struct kmem_cache *cachep)
> >   #ifdef CONFIG_DEBUG_PAGEALLOC
> >   static void slab_kernel_map(struct kmem_cache *cachep, void *objp, int map)
> >   {
> > -	if (!is_debug_pagealloc_cache(cachep))
> > -		return;
> > -
> > -	kernel_map_pages(virt_to_page(objp), cachep->size / PAGE_SIZE, map);
> > +	debug_pagealloc_map_pages(virt_to_page(objp),
> > +				  cachep->size / PAGE_SIZE, map);
> >   }
> >   #else
> > @@ -2062,7 +2060,7 @@ int __kmem_cache_create(struct kmem_cache *cachep, slab_flags_t flags)
> >   #if DEBUG
> >   	/*
> > -	 * If we're going to use the generic kernel_map_pages()
> > +	 * If we're going to use the generic debug_pagealloc_map_pages()
> >   	 * poisoning, then it's going to smash the contents of
> >   	 * the redzone and userword anyhow, so switch them off.
> >   	 */
> > 
> 

-- 
Sincerely yours,
Mike.

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[PATCH v4 2/4] PM: hibernate: make direct map manipulations more explicit

[Mike Rapoport]

From: Mike Rapoport <rppt@linux.ibm.com>

When DEBUG_PAGEALLOC or ARCH_HAS_SET_DIRECT_MAP is enabled a page may be
not present in the direct map and has to be explicitly mapped before it
could be copied.

Introduce hibernate_map_page() that will explicitly use
set_direct_map_{default,invalid}_noflush() for ARCH_HAS_SET_DIRECT_MAP case
and debug_pagealloc_map_pages() for DEBUG_PAGEALLOC case.

The remapping of the pages in safe_copy_page() presumes that it only
changes protection bits in an existing PTE and so it is safe to ignore
return value of set_direct_map_{default,invalid}_noflush().

Still, add a pr_warn() so that future changes in set_memory APIs will not
silently break hibernation.

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 include/linux/mm.h      | 12 ------------
 kernel/power/snapshot.c | 32 ++++++++++++++++++++++++++++++--
 2 files changed, 30 insertions(+), 14 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 1fc0609056dc..14e397f3752c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2927,16 +2927,6 @@ static inline bool debug_pagealloc_enabled_static(void)
 #if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_ARCH_HAS_SET_DIRECT_MAP)
 extern void __kernel_map_pages(struct page *page, int numpages, int enable);
 
-/*
- * When called in DEBUG_PAGEALLOC context, the call should most likely be
- * guarded by debug_pagealloc_enabled() or debug_pagealloc_enabled_static()
- */
-static inline void
-kernel_map_pages(struct page *page, int numpages, int enable)
-{
-	__kernel_map_pages(page, numpages, enable);
-}
-
 static inline void debug_pagealloc_map_pages(struct page *page,
 					     int numpages, int enable)
 {
@@ -2948,8 +2938,6 @@ static inline void debug_pagealloc_map_pages(struct page *page,
 extern bool kernel_page_present(struct page *page);
 #endif	/* CONFIG_HIBERNATION */
 #else	/* CONFIG_DEBUG_PAGEALLOC || CONFIG_ARCH_HAS_SET_DIRECT_MAP */
-static inline void
-kernel_map_pages(struct page *page, int numpages, int enable) {}
 static inline void debug_pagealloc_map_pages(struct page *page,
 					     int numpages, int enable) {}
 #ifdef CONFIG_HIBERNATION
diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
index 46b1804c1ddf..57d54b9d84bb 100644
--- a/kernel/power/snapshot.c
+++ b/kernel/power/snapshot.c
@@ -76,6 +76,34 @@ static inline void hibernate_restore_protect_page(void *page_address) {}
 static inline void hibernate_restore_unprotect_page(void *page_address) {}
 #endif /* CONFIG_STRICT_KERNEL_RWX  && CONFIG_ARCH_HAS_SET_MEMORY */
 
+static inline void hibernate_map_page(struct page *page, int enable)
+{
+	if (IS_ENABLED(CONFIG_ARCH_HAS_SET_DIRECT_MAP)) {
+		unsigned long addr = (unsigned long)page_address(page);
+		int ret;
+
+		/*
+		 * This should not fail because remapping a page here means
+		 * that we only update protection bits in an existing PTE.
+		 * It is still worth to have a warning here if something
+		 * changes and this will no longer be the case.
+		 */
+		if (enable)
+			ret = set_direct_map_default_noflush(page);
+		else
+			ret = set_direct_map_invalid_noflush(page);
+
+		if (ret) {
+			pr_warn_once("Failed to remap page\n");
+			return;
+		}
+
+		flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
+	} else {
+		debug_pagealloc_map_pages(page, 1, enable);
+	}
+}
+
 static int swsusp_page_is_free(struct page *);
 static void swsusp_set_page_forbidden(struct page *);
 static void swsusp_unset_page_forbidden(struct page *);
@@ -1355,9 +1383,9 @@ static void safe_copy_page(void *dst, struct page *s_page)
 	if (kernel_page_present(s_page)) {
 		do_copy_page(dst, page_address(s_page));
 	} else {
-		kernel_map_pages(s_page, 1, 1);
+		hibernate_map_page(s_page, 1);
 		do_copy_page(dst, page_address(s_page));
-		kernel_map_pages(s_page, 1, 0);
+		hibernate_map_page(s_page, 0);
 	}
 }
 
-- 
2.28.0


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Re: [PATCH v4 2/4] PM: hibernate: make direct map manipulations more explicit

[Vlastimil Babka]

On 11/3/20 5:20 PM, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>
> 
> When DEBUG_PAGEALLOC or ARCH_HAS_SET_DIRECT_MAP is enabled a page may be
> not present in the direct map and has to be explicitly mapped before it
> could be copied.
> 
> Introduce hibernate_map_page() that will explicitly use
> set_direct_map_{default,invalid}_noflush() for ARCH_HAS_SET_DIRECT_MAP case
> and debug_pagealloc_map_pages() for DEBUG_PAGEALLOC case.
> 
> The remapping of the pages in safe_copy_page() presumes that it only
> changes protection bits in an existing PTE and so it is safe to ignore
> return value of set_direct_map_{default,invalid}_noflush().
> 
> Still, add a pr_warn() so that future changes in set_memory APIs will not
> silently break hibernation.
> 
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Reviewed-by: David Hildenbrand <david@redhat.com>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

The bool param is a bit more acceptable here, being a private API. But if 
debug_pagealloc_map_pages() becomes split, then it might be easier to split this 
one too...

> ---
>   include/linux/mm.h      | 12 ------------
>   kernel/power/snapshot.c | 32 ++++++++++++++++++++++++++++++--
>   2 files changed, 30 insertions(+), 14 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 1fc0609056dc..14e397f3752c 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2927,16 +2927,6 @@ static inline bool debug_pagealloc_enabled_static(void)
>   #if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_ARCH_HAS_SET_DIRECT_MAP)
>   extern void __kernel_map_pages(struct page *page, int numpages, int enable);
>   
> -/*
> - * When called in DEBUG_PAGEALLOC context, the call should most likely be
> - * guarded by debug_pagealloc_enabled() or debug_pagealloc_enabled_static()
> - */
> -static inline void
> -kernel_map_pages(struct page *page, int numpages, int enable)
> -{
> -	__kernel_map_pages(page, numpages, enable);
> -}
> -
>   static inline void debug_pagealloc_map_pages(struct page *page,
>   					     int numpages, int enable)
>   {
> @@ -2948,8 +2938,6 @@ static inline void debug_pagealloc_map_pages(struct page *page,
>   extern bool kernel_page_present(struct page *page);
>   #endif	/* CONFIG_HIBERNATION */
>   #else	/* CONFIG_DEBUG_PAGEALLOC || CONFIG_ARCH_HAS_SET_DIRECT_MAP */
> -static inline void
> -kernel_map_pages(struct page *page, int numpages, int enable) {}
>   static inline void debug_pagealloc_map_pages(struct page *page,
>   					     int numpages, int enable) {}
>   #ifdef CONFIG_HIBERNATION
> diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
> index 46b1804c1ddf..57d54b9d84bb 100644
> --- a/kernel/power/snapshot.c
> +++ b/kernel/power/snapshot.c
> @@ -76,6 +76,34 @@ static inline void hibernate_restore_protect_page(void *page_address) {}
>   static inline void hibernate_restore_unprotect_page(void *page_address) {}
>   #endif /* CONFIG_STRICT_KERNEL_RWX  && CONFIG_ARCH_HAS_SET_MEMORY */
>   
> +static inline void hibernate_map_page(struct page *page, int enable)
> +{
> +	if (IS_ENABLED(CONFIG_ARCH_HAS_SET_DIRECT_MAP)) {
> +		unsigned long addr = (unsigned long)page_address(page);
> +		int ret;
> +
> +		/*
> +		 * This should not fail because remapping a page here means
> +		 * that we only update protection bits in an existing PTE.
> +		 * It is still worth to have a warning here if something
> +		 * changes and this will no longer be the case.
> +		 */
> +		if (enable)
> +			ret = set_direct_map_default_noflush(page);
> +		else
> +			ret = set_direct_map_invalid_noflush(page);
> +
> +		if (ret) {
> +			pr_warn_once("Failed to remap page\n");
> +			return;
> +		}
> +
> +		flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
> +	} else {
> +		debug_pagealloc_map_pages(page, 1, enable);
> +	}
> +}
> +
>   static int swsusp_page_is_free(struct page *);
>   static void swsusp_set_page_forbidden(struct page *);
>   static void swsusp_unset_page_forbidden(struct page *);
> @@ -1355,9 +1383,9 @@ static void safe_copy_page(void *dst, struct page *s_page)
>   	if (kernel_page_present(s_page)) {
>   		do_copy_page(dst, page_address(s_page));
>   	} else {
> -		kernel_map_pages(s_page, 1, 1);
> +		hibernate_map_page(s_page, 1);
>   		do_copy_page(dst, page_address(s_page));
> -		kernel_map_pages(s_page, 1, 0);
> +		hibernate_map_page(s_page, 0);
>   	}
>   }
>   
> 


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Re: [PATCH v4 2/4] PM: hibernate: make direct map manipulations more explicit

[Mike Rapoport]

On Wed, Nov 04, 2020 at 06:40:28PM +0100, Vlastimil Babka wrote:
> On 11/3/20 5:20 PM, Mike Rapoport wrote:
> > From: Mike Rapoport <rppt@linux.ibm.com>
> > 
> > When DEBUG_PAGEALLOC or ARCH_HAS_SET_DIRECT_MAP is enabled a page may be
> > not present in the direct map and has to be explicitly mapped before it
> > could be copied.
> > 
> > Introduce hibernate_map_page() that will explicitly use
> > set_direct_map_{default,invalid}_noflush() for ARCH_HAS_SET_DIRECT_MAP case
> > and debug_pagealloc_map_pages() for DEBUG_PAGEALLOC case.
> > 
> > The remapping of the pages in safe_copy_page() presumes that it only
> > changes protection bits in an existing PTE and so it is safe to ignore
> > return value of set_direct_map_{default,invalid}_noflush().
> > 
> > Still, add a pr_warn() so that future changes in set_memory APIs will not
> > silently break hibernation.
> > 
> > Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> > Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > Reviewed-by: David Hildenbrand <david@redhat.com>
> > Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> 
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
> 
> The bool param is a bit more acceptable here, being a private API. But if
> debug_pagealloc_map_pages() becomes split, then it might be easier to split
> this one too...

Let's split here as well.

> > ---
> >   include/linux/mm.h      | 12 ------------
> >   kernel/power/snapshot.c | 32 ++++++++++++++++++++++++++++++--
> >   2 files changed, 30 insertions(+), 14 deletions(-)
> > 
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index 1fc0609056dc..14e397f3752c 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -2927,16 +2927,6 @@ static inline bool debug_pagealloc_enabled_static(void)
> >   #if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_ARCH_HAS_SET_DIRECT_MAP)
> >   extern void __kernel_map_pages(struct page *page, int numpages, int enable);
> > -/*
> > - * When called in DEBUG_PAGEALLOC context, the call should most likely be
> > - * guarded by debug_pagealloc_enabled() or debug_pagealloc_enabled_static()
> > - */
> > -static inline void
> > -kernel_map_pages(struct page *page, int numpages, int enable)
> > -{
> > -	__kernel_map_pages(page, numpages, enable);
> > -}
> > -
> >   static inline void debug_pagealloc_map_pages(struct page *page,
> >   					     int numpages, int enable)
> >   {
> > @@ -2948,8 +2938,6 @@ static inline void debug_pagealloc_map_pages(struct page *page,
> >   extern bool kernel_page_present(struct page *page);
> >   #endif	/* CONFIG_HIBERNATION */
> >   #else	/* CONFIG_DEBUG_PAGEALLOC || CONFIG_ARCH_HAS_SET_DIRECT_MAP */
> > -static inline void
> > -kernel_map_pages(struct page *page, int numpages, int enable) {}
> >   static inline void debug_pagealloc_map_pages(struct page *page,
> >   					     int numpages, int enable) {}
> >   #ifdef CONFIG_HIBERNATION
> > diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
> > index 46b1804c1ddf..57d54b9d84bb 100644
> > --- a/kernel/power/snapshot.c
> > +++ b/kernel/power/snapshot.c
> > @@ -76,6 +76,34 @@ static inline void hibernate_restore_protect_page(void *page_address) {}
> >   static inline void hibernate_restore_unprotect_page(void *page_address) {}
> >   #endif /* CONFIG_STRICT_KERNEL_RWX  && CONFIG_ARCH_HAS_SET_MEMORY */
> > +static inline void hibernate_map_page(struct page *page, int enable)
> > +{
> > +	if (IS_ENABLED(CONFIG_ARCH_HAS_SET_DIRECT_MAP)) {
> > +		unsigned long addr = (unsigned long)page_address(page);
> > +		int ret;
> > +
> > +		/*
> > +		 * This should not fail because remapping a page here means
> > +		 * that we only update protection bits in an existing PTE.
> > +		 * It is still worth to have a warning here if something
> > +		 * changes and this will no longer be the case.
> > +		 */
> > +		if (enable)
> > +			ret = set_direct_map_default_noflush(page);
> > +		else
> > +			ret = set_direct_map_invalid_noflush(page);
> > +
> > +		if (ret) {
> > +			pr_warn_once("Failed to remap page\n");
> > +			return;
> > +		}
> > +
> > +		flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
> > +	} else {
> > +		debug_pagealloc_map_pages(page, 1, enable);
> > +	}
> > +}
> > +
> >   static int swsusp_page_is_free(struct page *);
> >   static void swsusp_set_page_forbidden(struct page *);
> >   static void swsusp_unset_page_forbidden(struct page *);
> > @@ -1355,9 +1383,9 @@ static void safe_copy_page(void *dst, struct page *s_page)
> >   	if (kernel_page_present(s_page)) {
> >   		do_copy_page(dst, page_address(s_page));
> >   	} else {
> > -		kernel_map_pages(s_page, 1, 1);
> > +		hibernate_map_page(s_page, 1);
> >   		do_copy_page(dst, page_address(s_page));
> > -		kernel_map_pages(s_page, 1, 0);
> > +		hibernate_map_page(s_page, 0);
> >   	}
> >   }
> > 
> 

-- 
Sincerely yours,
Mike.

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

[Mike Rapoport]

From: Mike Rapoport <rppt@linux.ibm.com>

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,
@@ -178,6 +178,7 @@ int set_direct_map_default_noflush(struct page *page)
 				   PAGE_SIZE, change_page_range, &data);
 }
 
+#ifdef CONFIG_DEBUG_PAGEALLOC
 void __kernel_map_pages(struct page *page, int numpages, int enable)
 {
 	if (!debug_pagealloc_enabled() && !rodata_full)
@@ -186,6 +187,7 @@ void __kernel_map_pages(struct page *page, int numpages, int enable)
 	set_memory_valid((unsigned long)page_address(page), numpages, enable);
 }
 
+#ifdef CONFIG_HIBERNATION
 /*
  * This function is used to determine if a linear map page has been marked as
  * not-valid. Walk the page table and check the PTE_VALID bit. This is based
@@ -232,3 +234,5 @@ bool kernel_page_present(struct page *page)
 	ptep = pte_offset_kernel(pmdp, addr);
 	return pte_valid(READ_ONCE(*ptep));
 }
+#endif /* CONFIG_HIBERNATION */
+#endif /* CONFIG_DEBUG_PAGEALLOC */
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index e9f13fe08492..ad8a83f3ddca 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -146,6 +146,7 @@ config PPC
 	select ARCH_MIGHT_HAVE_PC_SERIO
 	select ARCH_OPTIONAL_KERNEL_RWX		if ARCH_HAS_STRICT_KERNEL_RWX
 	select ARCH_SUPPORTS_ATOMIC_RMW
+	select ARCH_SUPPORTS_DEBUG_PAGEALLOC	if PPC32 || PPC_BOOK3S_64
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_CMPXCHG_LOCKREF		if PPC64
 	select ARCH_USE_QUEUED_RWLOCKS		if PPC_QUEUED_SPINLOCKS
@@ -355,10 +356,6 @@ config PPC_OF_PLATFORM_PCI
 	depends on PCI
 	depends on PPC64 # not supported on 32 bits yet
 
-config ARCH_SUPPORTS_DEBUG_PAGEALLOC
-	depends on PPC32 || PPC_BOOK3S_64
-	def_bool y
-
 config ARCH_SUPPORTS_UPROBES
 	def_bool y
 
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 44377fd7860e..9283c6f9ae2a 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -14,6 +14,7 @@ config RISCV
 	def_bool y
 	select ARCH_CLOCKSOURCE_INIT
 	select ARCH_SUPPORTS_ATOMIC_RMW
+	select ARCH_SUPPORTS_DEBUG_PAGEALLOC if MMU
 	select ARCH_HAS_BINFMT_FLAT
 	select ARCH_HAS_DEBUG_VM_PGTABLE
 	select ARCH_HAS_DEBUG_VIRTUAL if MMU
@@ -153,9 +154,6 @@ config ARCH_SELECT_MEMORY_MODEL
 config ARCH_WANT_GENERAL_HUGETLB
 	def_bool y
 
-config ARCH_SUPPORTS_DEBUG_PAGEALLOC
-	def_bool y
-
 config SYS_SUPPORTS_HUGETLBFS
 	depends on MMU
 	def_bool y
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index 183f1f4b2ae6..41a72861987c 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -461,8 +461,6 @@ static inline int ptep_clear_flush_young(struct vm_area_struct *vma,
 #define VMALLOC_START		0
 #define VMALLOC_END		TASK_SIZE
 
-static inline void __kernel_map_pages(struct page *page, int numpages, int enable) {}
-
 #endif /* !CONFIG_MMU */
 
 #define kern_addr_valid(addr)   (1) /* FIXME */
diff --git a/arch/riscv/mm/pageattr.c b/arch/riscv/mm/pageattr.c
index 19fecb362d81..321b09d2e2ea 100644
--- a/arch/riscv/mm/pageattr.c
+++ b/arch/riscv/mm/pageattr.c
@@ -184,6 +184,7 @@ int set_direct_map_default_noflush(struct page *page)
 	return ret;
 }
 
+#ifdef CONFIG_DEBUG_PAGEALLOC
 void __kernel_map_pages(struct page *page, int numpages, int enable)
 {
 	if (!debug_pagealloc_enabled())
@@ -196,3 +197,4 @@ void __kernel_map_pages(struct page *page, int numpages, int enable)
 		__set_memory((unsigned long)page_address(page), numpages,
 			     __pgprot(0), __pgprot(_PAGE_PRESENT));
 }
+#endif
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 4a2a12be04c9..991a850a6c0b 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -35,9 +35,6 @@ config GENERIC_LOCKBREAK
 config PGSTE
 	def_bool y if KVM
 
-config ARCH_SUPPORTS_DEBUG_PAGEALLOC
-	def_bool y
-
 config AUDIT_ARCH
 	def_bool y
 
@@ -106,6 +103,7 @@ config S390
 	select ARCH_INLINE_WRITE_UNLOCK_IRQRESTORE
 	select ARCH_STACKWALK
 	select ARCH_SUPPORTS_ATOMIC_RMW
+	select ARCH_SUPPORTS_DEBUG_PAGEALLOC
 	select ARCH_SUPPORTS_NUMA_BALANCING
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_CMPXCHG_LOCKREF
diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
index a6ca135442f9..2c729b8d097a 100644
--- a/arch/sparc/Kconfig
+++ b/arch/sparc/Kconfig
@@ -88,6 +88,7 @@ config SPARC64
 	select HAVE_C_RECORDMCOUNT
 	select HAVE_ARCH_AUDITSYSCALL
 	select ARCH_SUPPORTS_ATOMIC_RMW
+	select ARCH_SUPPORTS_DEBUG_PAGEALLOC
 	select HAVE_NMI
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select ARCH_USE_QUEUED_RWLOCKS
@@ -148,9 +149,6 @@ config GENERIC_ISA_DMA
 	bool
 	default y if SPARC32
 
-config ARCH_SUPPORTS_DEBUG_PAGEALLOC
-	def_bool y if SPARC64
-
 config PGTABLE_LEVELS
 	default 4 if 64BIT
 	default 3
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index f6946b81f74a..0db3fb1da70c 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -91,6 +91,7 @@ config X86
 	select ARCH_STACKWALK
 	select ARCH_SUPPORTS_ACPI
 	select ARCH_SUPPORTS_ATOMIC_RMW
+	select ARCH_SUPPORTS_DEBUG_PAGEALLOC
 	select ARCH_SUPPORTS_NUMA_BALANCING	if X86_64
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_QUEUED_RWLOCKS
@@ -329,9 +330,6 @@ config ZONE_DMA32
 config AUDIT_ARCH
 	def_bool y if X86_64
 
-config ARCH_SUPPORTS_DEBUG_PAGEALLOC
-	def_bool y
-
 config KASAN_SHADOW_OFFSET
 	hex
 	depends on KASAN
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 40baa90e74f4..bc9be96b777f 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -2194,6 +2194,7 @@ int set_direct_map_default_noflush(struct page *page)
 	return __set_pages_p(page, 1);
 }
 
+#ifdef CONFIG_DEBUG_PAGEALLOC
 void __kernel_map_pages(struct page *page, int numpages, int enable)
 {
 	if (PageHighMem(page))
@@ -2239,6 +2240,7 @@ bool kernel_page_present(struct page *page)
 	return (pte_val(*pte) & _PAGE_PRESENT);
 }
 #endif /* CONFIG_HIBERNATION */
+#endif /* CONFIG_DEBUG_PAGEALLOC */
 
 int __init kernel_map_pages_in_pgd(pgd_t *pgd, u64 pfn, unsigned long address,
 				   unsigned numpages, unsigned long page_flags)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 14e397f3752c..ab0ef6bd351d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2924,7 +2924,11 @@ static inline bool debug_pagealloc_enabled_static(void)
 	return static_branch_unlikely(&_debug_pagealloc_enabled);
 }
 
-#if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_ARCH_HAS_SET_DIRECT_MAP)
+#ifdef CONFIG_DEBUG_PAGEALLOC
+/*
+ * To support DEBUG_PAGEALLOC architecture must ensure that
+ * __kernel_map_pages() never fails
+ */
 extern void __kernel_map_pages(struct page *page, int numpages, int enable);
 
 static inline void debug_pagealloc_map_pages(struct page *page,
@@ -2937,13 +2941,13 @@ static inline void debug_pagealloc_map_pages(struct page *page,
 #ifdef CONFIG_HIBERNATION
 extern bool kernel_page_present(struct page *page);
 #endif	/* CONFIG_HIBERNATION */
-#else	/* CONFIG_DEBUG_PAGEALLOC || CONFIG_ARCH_HAS_SET_DIRECT_MAP */
+#else	/* CONFIG_DEBUG_PAGEALLOC */
 static inline void debug_pagealloc_map_pages(struct page *page,
 					     int numpages, int enable) {}
 #ifdef CONFIG_HIBERNATION
 static inline bool kernel_page_present(struct page *page) { return true; }
 #endif	/* CONFIG_HIBERNATION */
-#endif	/* CONFIG_DEBUG_PAGEALLOC || CONFIG_ARCH_HAS_SET_DIRECT_MAP */
+#endif	/* CONFIG_DEBUG_PAGEALLOC */
 
 #ifdef __HAVE_ARCH_GATE_AREA
 extern struct vm_area_struct *get_gate_vma(struct mm_struct *mm);
-- 
2.28.0


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

[Vlastimil Babka]

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

[Mike Rapoport]

On Wed, Nov 04, 2020 at 07:02:20PM +0100, Vlastimil Babka wrote:
> 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()?

I was confused about this for quite a long :)

On arm64 the changes to direct^w linear map are allowed when 

	debug_page_alloc() || rodata_full

In hibernation we essentially have now

	if (1)
		set_direct_map(something)
	else
		debug_page_alloc_map()

With debug_pagealloc enabled but with rodata_full disabled arm64
versions of set_direct_map_*() will become a nop, so a page that was
unmapped by debug_pagealloc() will not be mapped back.

I'm still puzzled how hibernation might ever need to save a free page,
but that's another story.

-- 
Sincerely yours,
Mike.

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[PATCH v4 4/4] arch, mm: make kernel_page_present() always available

[Mike Rapoport]

From: Mike Rapoport <rppt@linux.ibm.com>

For architectures that enable ARCH_HAS_SET_MEMORY having the ability to
verify that a page is mapped in the kernel direct map can be useful
regardless of hibernation.

Add RISC-V implementation of kernel_page_present(), update its forward
declarations and stubs to be a part of set_memory API and remove ugly
ifdefery in inlcude/linux/mm.h around current declarations of
kernel_page_present().

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/arm64/include/asm/cacheflush.h |  1 +
 arch/arm64/mm/pageattr.c            |  4 +---
 arch/riscv/include/asm/set_memory.h |  1 +
 arch/riscv/mm/pageattr.c            | 29 +++++++++++++++++++++++++++++
 arch/x86/include/asm/set_memory.h   |  1 +
 arch/x86/mm/pat/set_memory.c        |  4 +---
 include/linux/mm.h                  |  7 -------
 include/linux/set_memory.h          |  5 +++++
 8 files changed, 39 insertions(+), 13 deletions(-)

diff --git a/arch/arm64/include/asm/cacheflush.h b/arch/arm64/include/asm/cacheflush.h
index 9384fd8fc13c..45217f21f1fe 100644
--- a/arch/arm64/include/asm/cacheflush.h
+++ b/arch/arm64/include/asm/cacheflush.h
@@ -140,6 +140,7 @@ int set_memory_valid(unsigned long addr, int numpages, int enable);
 
 int set_direct_map_invalid_noflush(struct page *page);
 int set_direct_map_default_noflush(struct page *page);
+bool kernel_page_present(struct page *page);
 
 #include <asm-generic/cacheflush.h>
 
diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index 439325532be1..92eccaf595c8 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -186,8 +186,8 @@ void __kernel_map_pages(struct page *page, int numpages, int enable)
 
 	set_memory_valid((unsigned long)page_address(page), numpages, enable);
 }
+#endif /* CONFIG_DEBUG_PAGEALLOC */
 
-#ifdef CONFIG_HIBERNATION
 /*
  * This function is used to determine if a linear map page has been marked as
  * not-valid. Walk the page table and check the PTE_VALID bit. This is based
@@ -234,5 +234,3 @@ bool kernel_page_present(struct page *page)
 	ptep = pte_offset_kernel(pmdp, addr);
 	return pte_valid(READ_ONCE(*ptep));
 }
-#endif /* CONFIG_HIBERNATION */
-#endif /* CONFIG_DEBUG_PAGEALLOC */
diff --git a/arch/riscv/include/asm/set_memory.h b/arch/riscv/include/asm/set_memory.h
index 4c5bae7ca01c..d690b08dff2a 100644
--- a/arch/riscv/include/asm/set_memory.h
+++ b/arch/riscv/include/asm/set_memory.h
@@ -24,6 +24,7 @@ static inline int set_memory_nx(unsigned long addr, int numpages) { return 0; }
 
 int set_direct_map_invalid_noflush(struct page *page);
 int set_direct_map_default_noflush(struct page *page);
+bool kernel_page_present(struct page *page);
 
 #endif /* __ASSEMBLY__ */
 
diff --git a/arch/riscv/mm/pageattr.c b/arch/riscv/mm/pageattr.c
index 321b09d2e2ea..87ba5a68bbb8 100644
--- a/arch/riscv/mm/pageattr.c
+++ b/arch/riscv/mm/pageattr.c
@@ -198,3 +198,32 @@ void __kernel_map_pages(struct page *page, int numpages, int enable)
 			     __pgprot(0), __pgprot(_PAGE_PRESENT));
 }
 #endif
+
+bool kernel_page_present(struct page *page)
+{
+	unsigned long addr = (unsigned long)page_address(page);
+	pgd_t *pgd;
+	pud_t *pud;
+	p4d_t *p4d;
+	pmd_t *pmd;
+	pte_t *pte;
+
+	pgd = pgd_offset_k(addr);
+	if (!pgd_present(*pgd))
+		return false;
+
+	p4d = p4d_offset(pgd, addr);
+	if (!p4d_present(*p4d))
+		return false;
+
+	pud = pud_offset(p4d, addr);
+	if (!pud_present(*pud))
+		return false;
+
+	pmd = pmd_offset(pud, addr);
+	if (!pmd_present(*pmd))
+		return false;
+
+	pte = pte_offset_kernel(pmd, addr);
+	return pte_present(*pte);
+}
diff --git a/arch/x86/include/asm/set_memory.h b/arch/x86/include/asm/set_memory.h
index 5948218f35c5..4352f08bfbb5 100644
--- a/arch/x86/include/asm/set_memory.h
+++ b/arch/x86/include/asm/set_memory.h
@@ -82,6 +82,7 @@ int set_pages_rw(struct page *page, int numpages);
 
 int set_direct_map_invalid_noflush(struct page *page);
 int set_direct_map_default_noflush(struct page *page);
+bool kernel_page_present(struct page *page);
 
 extern int kernel_set_to_readonly;
 
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index bc9be96b777f..16f878c26667 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -2226,8 +2226,8 @@ void __kernel_map_pages(struct page *page, int numpages, int enable)
 
 	arch_flush_lazy_mmu_mode();
 }
+#endif /* CONFIG_DEBUG_PAGEALLOC */
 
-#ifdef CONFIG_HIBERNATION
 bool kernel_page_present(struct page *page)
 {
 	unsigned int level;
@@ -2239,8 +2239,6 @@ bool kernel_page_present(struct page *page)
 	pte = lookup_address((unsigned long)page_address(page), &level);
 	return (pte_val(*pte) & _PAGE_PRESENT);
 }
-#endif /* CONFIG_HIBERNATION */
-#endif /* CONFIG_DEBUG_PAGEALLOC */
 
 int __init kernel_map_pages_in_pgd(pgd_t *pgd, u64 pfn, unsigned long address,
 				   unsigned numpages, unsigned long page_flags)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index ab0ef6bd351d..44b82f22e76a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2937,16 +2937,9 @@ static inline void debug_pagealloc_map_pages(struct page *page,
 	if (debug_pagealloc_enabled_static())
 		__kernel_map_pages(page, numpages, enable);
 }
-
-#ifdef CONFIG_HIBERNATION
-extern bool kernel_page_present(struct page *page);
-#endif	/* CONFIG_HIBERNATION */
 #else	/* CONFIG_DEBUG_PAGEALLOC */
 static inline void debug_pagealloc_map_pages(struct page *page,
 					     int numpages, int enable) {}
-#ifdef CONFIG_HIBERNATION
-static inline bool kernel_page_present(struct page *page) { return true; }
-#endif	/* CONFIG_HIBERNATION */
 #endif	/* CONFIG_DEBUG_PAGEALLOC */
 
 #ifdef __HAVE_ARCH_GATE_AREA
diff --git a/include/linux/set_memory.h b/include/linux/set_memory.h
index 860e0f843c12..fe1aa4e54680 100644
--- a/include/linux/set_memory.h
+++ b/include/linux/set_memory.h
@@ -23,6 +23,11 @@ static inline int set_direct_map_default_noflush(struct page *page)
 {
 	return 0;
 }
+
+static inline bool kernel_page_present(struct page *page)
+{
+	return true;
+}
 #endif
 
 #ifndef set_mce_nospec
-- 
2.28.0


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