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Date: Fri, 13 Nov 2020 13:08:50 +0100
From: David Hildenbrand <david@...hat.com>
To: Vlastimil Babka <vbabka@...e.cz>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
Alexander Potapenko <glider@...gle.com>,
Kees Cook <keescook@...omium.org>,
Michal Hocko <mhocko@...nel.org>,
Mateusz Nosek <mateusznosek0@...il.com>,
Laura Abbott <labbott@...nel.org>
Subject: Re: [PATCH v3 2/5] mm, page_poison: use static key more efficiently
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@...e.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@...hat.com>
--
Thanks,
David / dhildenb
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