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Message-ID: <4dea1223-a2bf-89ec-afe7-72a3218e61a9@redhat.com>
Date: Thu, 12 Nov 2020 17:06:38 +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 v2 2/5] mm, page_poison: use static key more efficiently
On 12.11.20 15:37, Vlastimil Babka wrote:
> On 11/11/20 4:38 PM, David Hildenbrand wrote:
>> On 03.11.20 16:22, 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().
>>
>> [...]
>>
>>> + * 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));
>>
>> As already mentioned IIRC:
>
> Yes, it was, and I thought I fixed it. Guess not.
>
>> return static_branch_unlikely(&_page_poisoning_enabled);
>>
>>> +}
>
>>> @@ -1260,7 +1271,8 @@ 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);
>>> + if (page_poisoning_enabled_static())
>>> + kernel_poison_pages(page, 1 << order);
>>
>> This would look much better by having kernel_poison_pages() simply be
>> implemented in a header, where the static check is performed.
>>
>> Take a look at how it's handled in mm/shuffle.h
>
> Ok. Fixup below.
>
> ----8<----
>
> From 7ce26ba61296f583f0f9089e7887f07424f25d2c Mon Sep 17 00:00:00 2001
> From: Vlastimil Babka <vbabka@...e.cz>
> Date: Thu, 12 Nov 2020 15:20:58 +0100
> Subject: [PATCH] mm, page_poison: use static key more efficiently-fix
>
> Non-functional cleanups, per David Hildenbrand.
>
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> ---
> include/linux/mm.h | 16 +++++++++++++---
> mm/page_alloc.c | 7 +++----
> mm/page_poison.c | 4 ++--
> 3 files changed, 18 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 4d6dd9f44571..861b9392b5dc 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2867,8 +2867,8 @@ extern int apply_to_existing_page_range(struct mm_struct *mm,
>
> extern void init_mem_debugging_and_hardening(void);
> #ifdef CONFIG_PAGE_POISONING
> -extern void kernel_poison_pages(struct page *page, int numpages);
> -extern void kernel_unpoison_pages(struct page *page, int numpages);
> +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)
> @@ -2881,7 +2881,17 @@ static inline bool page_poisoning_enabled(void)
> */
> static inline bool page_poisoning_enabled_static(void)
> {
> - return (static_branch_unlikely(&_page_poisoning_enabled));
> + 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; }
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index fd7f9345adc0..1388b5939551 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1271,8 +1271,8 @@ static __always_inline bool free_pages_prepare(struct page *page,
> if (want_init_on_free())
> kernel_init_free_pages(page, 1 << order);
>
> - if (page_poisoning_enabled_static())
> - kernel_poison_pages(page, 1 << order);
> + 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
> @@ -2281,8 +2281,7 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
> if (debug_pagealloc_enabled_static())
> kernel_map_pages(page, 1 << order, 1);
> kasan_alloc_pages(page, order);
> - if (page_poisoning_enabled_static())
> - kernel_unpoison_pages(page, 1 << order);
> + 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 dd7aeada036f..4d75fc9ccc7a 100644
> --- a/mm/page_poison.c
> +++ b/mm/page_poison.c
> @@ -30,7 +30,7 @@ static void poison_page(struct page *page)
> kunmap_atomic(addr);
> }
>
> -void kernel_poison_pages(struct page *page, int n)
> +void __kernel_poison_pages(struct page *page, int n)
> {
> int i;
>
> @@ -89,7 +89,7 @@ static void unpoison_page(struct page *page)
> kunmap_atomic(addr);
> }
>
> -void kernel_unpoison_pages(struct page *page, int n)
> +void __kernel_unpoison_pages(struct page *page, int n)
> {
> int i;
>
>
LGTM.
--
Thanks,
David / dhildenb
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