Re: [PATCH v3 2/5] mm, page_poison: use static key more efficiently
From: David Hildenbrand
Date: Fri Nov 13 2020 - 07:09:06 EST
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@xxxxxxx>
---
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@xxxxxxxxxx>
--
Thanks,
David / dhildenb