Re: [PATCH v3 2/5] mm, page_poison: use static key more efficiently

[David Hildenbrand <david@redhat.com>]

On 13.11.20 11:40, Vlastimil Babka wrote:
> Commit 11c9c7edae06 ("mm/page_poison.c: replace bool variable with static key")
> changed page_poisoning_enabled() to a static key check. However, the function
> is not inlined, so each check still involves a function call with overhead not
> eliminated when page poisoning is disabled.
> 
> Analogically to how debug_pagealloc is handled, this patch converts
> page_poisoning_enabled() back to boolean check, and introduces
> page_poisoning_enabled_static() for fast paths. Both functions are inlined.
> 
> The function kernel_poison_pages() is also called unconditionally and does
> the static key check inside. Remove it from there and put it to callers. Also
> split it to two functions kernel_poison_pages() and kernel_unpoison_pages()
> instead of the confusing bool parameter.
> 
> Also optimize the check that enables page poisoning instead of debug_pagealloc
> for architectures without proper debug_pagealloc support. Move the check to
> init_mem_debugging_and_hardening() to enable a single static key instead of
> having two static branches in page_poisoning_enabled_static().
> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> ---
>   drivers/virtio/virtio_balloon.c |  2 +-
>   include/linux/mm.h              | 33 +++++++++++++++++---
>   mm/page_alloc.c                 | 18 +++++++++--
>   mm/page_poison.c                | 53 +++++----------------------------
>   4 files changed, 52 insertions(+), 54 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 481611c09dae..e53faed6ba93 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -1116,7 +1116,7 @@ static int virtballoon_validate(struct virtio_device *vdev)
>   	 */
>   	if (!want_init_on_free() &&
>   	    (IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY) ||
> -	     !page_poisoning_enabled()))
> +	     !page_poisoning_enabled_static()))
>   		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_POISON);
>   	else if (!virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON))
>   		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_REPORTING);
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 82ab5c894d94..5ab5358be2b3 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2862,12 +2862,37 @@ extern int apply_to_existing_page_range(struct mm_struct *mm,
>   
>   extern void init_mem_debugging_and_hardening(void);
>   #ifdef CONFIG_PAGE_POISONING
> -extern bool page_poisoning_enabled(void);
> -extern void kernel_poison_pages(struct page *page, int numpages, int enable);
> +extern void __kernel_poison_pages(struct page *page, int numpages);
> +extern void __kernel_unpoison_pages(struct page *page, int numpages);
> +extern bool _page_poisoning_enabled_early;
> +DECLARE_STATIC_KEY_FALSE(_page_poisoning_enabled);
> +static inline bool page_poisoning_enabled(void)
> +{
> +	return _page_poisoning_enabled_early;
> +}
> +/*
> + * For use in fast paths after init_mem_debugging() has run, or when a
> + * false negative result is not harmful when called too early.
> + */
> +static inline bool page_poisoning_enabled_static(void)
> +{
> +	return static_branch_unlikely(&_page_poisoning_enabled);
> +}
> +static inline void kernel_poison_pages(struct page *page, int numpages)
> +{
> +	if (page_poisoning_enabled_static())
> +		__kernel_poison_pages(page, numpages);
> +}
> +static inline void kernel_unpoison_pages(struct page *page, int numpages)
> +{
> +	if (page_poisoning_enabled_static())
> +		__kernel_unpoison_pages(page, numpages);
> +}
>   #else
>   static inline bool page_poisoning_enabled(void) { return false; }
> -static inline void kernel_poison_pages(struct page *page, int numpages,
> -					int enable) { }
> +static inline bool page_poisoning_enabled_static(void) { return false; }
> +static inline void kernel_poison_pages(struct page *page, int numpages) { }
> +static inline void kernel_unpoison_pages(struct page *page, int numpages) { }
>   #endif
>   
>   DECLARE_STATIC_KEY_FALSE(init_on_alloc);
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 567060c2ad83..cd966829bed3 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -775,6 +775,17 @@ void init_mem_debugging_and_hardening(void)
>   			static_branch_enable(&init_on_free);
>   	}
>   
> +#ifdef CONFIG_PAGE_POISONING
> +	/*
> +	 * Page poisoning is debug page alloc for some arches. If
> +	 * either of those options are enabled, enable poisoning.
> +	 */
> +	if (page_poisoning_enabled() ||
> +	     (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC) &&
> +	      debug_pagealloc_enabled()))
> +		static_branch_enable(&_page_poisoning_enabled);
> +#endif
> +
>   #ifdef CONFIG_DEBUG_PAGEALLOC
>   	if (!debug_pagealloc_enabled())
>   		return;
> @@ -1262,7 +1273,8 @@ static __always_inline bool free_pages_prepare(struct page *page,
>   	if (want_init_on_free())
>   		kernel_init_free_pages(page, 1 << order);
>   
> -	kernel_poison_pages(page, 1 << order, 0);
> +	kernel_poison_pages(page, 1 << order);
> +
>   	/*
>   	 * arch_free_page() can make the page's contents inaccessible.  s390
>   	 * does this.  So nothing which can access the page's contents should
> @@ -2217,7 +2229,7 @@ static inline int check_new_page(struct page *page)
>   static inline bool free_pages_prezeroed(void)
>   {
>   	return (IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) &&
> -		page_poisoning_enabled()) || want_init_on_free();
> +		page_poisoning_enabled_static()) || want_init_on_free();
>   }
>   
>   #ifdef CONFIG_DEBUG_VM
> @@ -2279,7 +2291,7 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
>   	arch_alloc_page(page, order);
>   	debug_pagealloc_map_pages(page, 1 << order);
>   	kasan_alloc_pages(page, order);
> -	kernel_poison_pages(page, 1 << order, 1);
> +	kernel_unpoison_pages(page, 1 << order);
>   	set_page_owner(page, order, gfp_flags);
>   }
>   
> diff --git a/mm/page_poison.c b/mm/page_poison.c
> index e6c994af7518..0d899a01d107 100644
> --- a/mm/page_poison.c
> +++ b/mm/page_poison.c
> @@ -8,45 +8,17 @@
>   #include <linux/ratelimit.h>
>   #include <linux/kasan.h>
>   
> -static DEFINE_STATIC_KEY_FALSE_RO(want_page_poisoning);
> +bool _page_poisoning_enabled_early;
> +EXPORT_SYMBOL(_page_poisoning_enabled_early);
> +DEFINE_STATIC_KEY_FALSE(_page_poisoning_enabled);
> +EXPORT_SYMBOL(_page_poisoning_enabled);
>   
>   static int __init early_page_poison_param(char *buf)
>   {
> -	int ret;
> -	bool tmp;
> -
> -	ret = strtobool(buf, &tmp);
> -	if (ret)
> -		return ret;
> -
> -	if (tmp)
> -		static_branch_enable(&want_page_poisoning);
> -	else
> -		static_branch_disable(&want_page_poisoning);
> -
> -	return 0;
> +	return kstrtobool(buf, &_page_poisoning_enabled_early);
>   }
>   early_param("page_poison", early_page_poison_param);
>   
> -/**
> - * page_poisoning_enabled - check if page poisoning is enabled
> - *
> - * Return true if page poisoning is enabled, or false if not.
> - */
> -bool page_poisoning_enabled(void)
> -{
> -	/*
> -	 * Assumes that debug_pagealloc_enabled is set before
> -	 * memblock_free_all.
> -	 * Page poisoning is debug page alloc for some arches. If
> -	 * either of those options are enabled, enable poisoning.
> -	 */
> -	return (static_branch_unlikely(&want_page_poisoning) ||
> -		(!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC) &&
> -		debug_pagealloc_enabled()));
> -}
> -EXPORT_SYMBOL_GPL(page_poisoning_enabled);
> -
>   static void poison_page(struct page *page)
>   {
>   	void *addr = kmap_atomic(page);
> @@ -58,7 +30,7 @@ static void poison_page(struct page *page)
>   	kunmap_atomic(addr);
>   }
>   
> -static void poison_pages(struct page *page, int n)
> +void __kernel_poison_pages(struct page *page, int n)
>   {
>   	int i;
>   
> @@ -117,7 +89,7 @@ static void unpoison_page(struct page *page)
>   	kunmap_atomic(addr);
>   }
>   
> -static void unpoison_pages(struct page *page, int n)
> +void __kernel_unpoison_pages(struct page *page, int n)
>   {
>   	int i;
>   
> @@ -125,17 +97,6 @@ static void unpoison_pages(struct page *page, int n)
>   		unpoison_page(page + i);
>   }
>   
> -void kernel_poison_pages(struct page *page, int numpages, int enable)
> -{
> -	if (!page_poisoning_enabled())
> -		return;
> -
> -	if (enable)
> -		unpoison_pages(page, numpages);
> -	else
> -		poison_pages(page, numpages);
> -}
> -
>   #ifndef CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC
>   void __kernel_map_pages(struct page *page, int numpages, int enable)
>   {
> 

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb