mm, page_alloc: do not rely on the order of page_poison and init_on_alloc/free parameters

Patch series "cleanup page poisoning", v3.

I have identified a number of issues and opportunities for cleanup with
CONFIG_PAGE_POISON and friends:

 - interaction with init_on_alloc and init_on_free parameters depends on
   the order of parameters (Patch 1)

 - the boot time enabling uses static key, but inefficienty (Patch 2)

 - sanity checking is incompatible with hibernation (Patch 3)

 - CONFIG_PAGE_POISONING_NO_SANITY can be removed now that we have
   init_on_free (Patch 4)

 - CONFIG_PAGE_POISONING_ZERO can be most likely removed now that we
   have init_on_free (Patch 5)

This patch (of 5):

Enabling page_poison=1 together with init_on_alloc=1 or init_on_free=1
produces a warning in dmesg that page_poison takes precedence.  However,
as these warnings are printed in early_param handlers for
init_on_alloc/free, they are not printed if page_poison is enabled later
on the command line (handlers are called in the order of their
parameters), or when init_on_alloc/free is always enabled by the
respective config option - before the page_poison early param handler is
called, it is not considered to be enabled.  This is inconsistent.

We can remove the dependency on order by making the init_on_* parameters
only set a boolean variable, and postponing the evaluation after all early
params have been processed.  Introduce a new
init_mem_debugging_and_hardening() function for that, and move the related
debug_pagealloc processing there as well.

As a result init_mem_debugging_and_hardening() knows always accurately if
init_on_* and/or page_poison options were enabled.  Thus we can also
optimize want_init_on_alloc() and want_init_on_free().  We don't need to
check page_poisoning_enabled() there, we can instead not enable the
init_on_* static keys at all, if page poisoning is enabled.  This results
in a simpler and more effective code.

Link: https://lkml.kernel.org/r/20201113104033.22907-1-vbabka@suse.cz
Link: https://lkml.kernel.org/r/20201113104033.22907-2-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mateusz Nosek <mateusznosek0@gmail.com>
Cc: Laura Abbott <labbott@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5ec79757eeaea57cf3ff40553be94d2576eb4ee4..591c784277ea149153ca018414a5ba2b48828aa2 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2872,6 +2872,7 @@ extern int apply_to_existing_page_range(struct mm_struct *mm,
                                   unsigned long address, unsigned long size,
                                   pte_fn_t fn, void *data);
 
+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);
@@ -2881,35 +2882,20 @@ static inline void kernel_poison_pages(struct page *page, int numpages,
                                        int enable) { }
 #endif
 
-#ifdef CONFIG_INIT_ON_ALLOC_DEFAULT_ON
-DECLARE_STATIC_KEY_TRUE(init_on_alloc);
-#else
 DECLARE_STATIC_KEY_FALSE(init_on_alloc);
-#endif
 static inline bool want_init_on_alloc(gfp_t flags)
 {
-       if (static_branch_unlikely(&init_on_alloc) &&
-           !page_poisoning_enabled())
+       if (static_branch_unlikely(&init_on_alloc))
                return true;
        return flags & __GFP_ZERO;
 }
 
-#ifdef CONFIG_INIT_ON_FREE_DEFAULT_ON
-DECLARE_STATIC_KEY_TRUE(init_on_free);
-#else
 DECLARE_STATIC_KEY_FALSE(init_on_free);
-#endif
 static inline bool want_init_on_free(void)
 {
-       return static_branch_unlikely(&init_on_free) &&
-              !page_poisoning_enabled();
+       return static_branch_unlikely(&init_on_free);
 }
 
-#ifdef CONFIG_DEBUG_PAGEALLOC
-extern void init_debug_pagealloc(void);
-#else
-static inline void init_debug_pagealloc(void) {}
-#endif
 extern bool _debug_pagealloc_enabled_early;
 DECLARE_STATIC_KEY_FALSE(_debug_pagealloc_enabled);
 

diff --git a/init/main.c b/init/main.c
index 404366e1a64db0e19a9af78db1c18a43266ea43c..3024c4db17a92d585b0cb2fc0074acbf9d5b70a9 100644 (file)
--- a/init/main.c
+++ b/init/main.c
@@ -824,7 +824,7 @@ static void __init mm_init(void)
         * bigger than MAX_ORDER unless SPARSEMEM.
         */
        page_ext_init_flatmem();
-       init_debug_pagealloc();
+       init_mem_debugging_and_hardening();
        report_meminit();
        mem_init();
        /* page_owner must be initialized after buddy is ready */

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 521d29718c9e74b8efda5def049aad336140a630..3fd0c8d5745f2bd446fc440fea29f7879a7a1ca2 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -167,53 +167,26 @@ unsigned long totalcma_pages __read_mostly;
 
 int percpu_pagelist_fraction;
 gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK;
-#ifdef CONFIG_INIT_ON_ALLOC_DEFAULT_ON
-DEFINE_STATIC_KEY_TRUE(init_on_alloc);
-#else
 DEFINE_STATIC_KEY_FALSE(init_on_alloc);
-#endif
 EXPORT_SYMBOL(init_on_alloc);
 
-#ifdef CONFIG_INIT_ON_FREE_DEFAULT_ON
-DEFINE_STATIC_KEY_TRUE(init_on_free);
-#else
 DEFINE_STATIC_KEY_FALSE(init_on_free);
-#endif
 EXPORT_SYMBOL(init_on_free);
 
+static bool _init_on_alloc_enabled_early __read_mostly
+                               = IS_ENABLED(CONFIG_INIT_ON_ALLOC_DEFAULT_ON);
 static int __init early_init_on_alloc(char *buf)
 {
-       int ret;
-       bool bool_result;
 
-       ret = kstrtobool(buf, &bool_result);
-       if (ret)
-               return ret;
-       if (bool_result && page_poisoning_enabled())
-               pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, will take precedence over init_on_alloc\n");
-       if (bool_result)
-               static_branch_enable(&init_on_alloc);
-       else
-               static_branch_disable(&init_on_alloc);
-       return 0;
+       return kstrtobool(buf, &_init_on_alloc_enabled_early);
 }
 early_param("init_on_alloc", early_init_on_alloc);
 
+static bool _init_on_free_enabled_early __read_mostly
+                               = IS_ENABLED(CONFIG_INIT_ON_FREE_DEFAULT_ON);
 static int __init early_init_on_free(char *buf)
 {
-       int ret;
-       bool bool_result;
-
-       ret = kstrtobool(buf, &bool_result);
-       if (ret)
-               return ret;
-       if (bool_result && page_poisoning_enabled())
-               pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, will take precedence over init_on_free\n");
-       if (bool_result)
-               static_branch_enable(&init_on_free);
-       else
-               static_branch_disable(&init_on_free);
-       return 0;
+       return kstrtobool(buf, &_init_on_free_enabled_early);
 }
 early_param("init_on_free", early_init_on_free);
 
@@ -730,19 +703,6 @@ static int __init early_debug_pagealloc(char *buf)
 }
 early_param("debug_pagealloc", early_debug_pagealloc);
 
-void init_debug_pagealloc(void)
-{
-       if (!debug_pagealloc_enabled())
-               return;
-
-       static_branch_enable(&_debug_pagealloc_enabled);
-
-       if (!debug_guardpage_minorder())
-               return;
-
-       static_branch_enable(&_debug_guardpage_enabled);
-}
-
 static int __init debug_guardpage_minorder_setup(char *buf)
 {
        unsigned long res;
@@ -794,6 +754,42 @@ static inline void clear_page_guard(struct zone *zone, struct page *page,
                                unsigned int order, int migratetype) {}
 #endif
 
+/*
+ * Enable static keys related to various memory debugging and hardening options.
+ * Some override others, and depend on early params that are evaluated in the
+ * order of appearance. So we need to first gather the full picture of what was
+ * enabled, and then make decisions.
+ */
+void init_mem_debugging_and_hardening(void)
+{
+       if (_init_on_alloc_enabled_early) {
+               if (page_poisoning_enabled())
+                       pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, "
+                               "will take precedence over init_on_alloc\n");
+               else
+                       static_branch_enable(&init_on_alloc);
+       }
+       if (_init_on_free_enabled_early) {
+               if (page_poisoning_enabled())
+                       pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, "
+                               "will take precedence over init_on_free\n");
+               else
+                       static_branch_enable(&init_on_free);
+       }
+
+#ifdef CONFIG_DEBUG_PAGEALLOC
+       if (!debug_pagealloc_enabled())
+               return;
+
+       static_branch_enable(&_debug_pagealloc_enabled);
+
+       if (!debug_guardpage_minorder())
+               return;
+
+       static_branch_enable(&_debug_guardpage_enabled);
+#endif
+}
+
 static inline void set_buddy_order(struct page *page, unsigned int order)
 {
        set_page_private(page, order);