mm: hugetlb_vmemmap: introduce CONFIG_HUGETLB_PAGE_HAS_OPTIMIZE_VMEMMAP

If the size of "struct page" is not the power of two but with the feature of minimizing overhead of struct page associated with each HugeTLB is enabled, then the vmemmap pages of HugeTLB will be corrupted after remapping (panic is about to happen in theory). But this only exists when !CONFIG_MEMCG && !CONFIG_SLUB on x86_64. However, it is not a conventional configuration nowadays. So it is not a real word issue, just the result of a code review. But we have to prevent anyone from configuring that combined configurations. In order to avoid many checks like "is_power_of_2 (sizeof(struct page))" through mm/hugetlb_vmemmap.c. Introduce a new macro CONFIG_HUGETLB_PAGE_HAS_OPTIMIZE_VMEMMAP to represent the size of struct page is power of two and CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP is configured. Then make the codes of this feature depends on this new macro. Then we could prevent anyone do any unexpected configurations. A new autoconf_ext.h is introduced as well, which serves as an extension for autoconf.h since those special configurations (e.g. CONFIG_HUGETLB_PAGE_HAS_OPTIMIZE_VMEMMAP here) are rely on the autoconf.h (generated from Kconfig), so we cannot embed those configurations into Kconfig. After this change, it would be easy if someone want to do the similar thing (add a new CONFIG) in the future. Signed-off-by: Muchun Song <songmuchun@bytedance.com> Suggested-by: Luis Chamberlain <mcgrof@kernel.org>
intel-lab-lkp · Apr 12, 2022 · bb63a01 · bb63a01
1 parent 71e0d84
commit bb63a01
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Showing 11 changed files with 61 additions and 14 deletions.
diff --git a/Kbuild b/Kbuild
@@ -2,6 +2,12 @@
 #
 # Kbuild for top-level directory of the kernel
 
+# autoconf_ext.h is generated last since it depends on other generated headers,
+# however those other generated headers may include autoconf_ext.h. Use the
+# following macro to avoid circular dependency.
+
+KBUILD_CFLAGS_KERNEL += -D__EXCLUDE_AUTOCONF_EXT_H
+
 #####
 # Generate bounds.h
 
@@ -36,6 +42,19 @@ arch/$(SRCARCH)/kernel/asm-offsets.s: $(timeconst-file) $(bounds-file)
 $(offsets-file): arch/$(SRCARCH)/kernel/asm-offsets.s FORCE
 	$(call filechk,offsets,__ASM_OFFSETS_H__)
 
+#####
+# Generate autoconf_ext.h.
+
+autoconf_ext-file := include/generated/autoconf_ext.h
+
+always-y += $(autoconf_ext-file)
+targets += kernel/autoconf_ext.s
+
+kernel/autoconf_ext.s: $(bounds-file) $(timeconst-file) $(offsets-file)
+
+$(autoconf_ext-file): kernel/autoconf_ext.s FORCE
+	$(call filechk,offsets,__LINUX_AUTOCONF_EXT_H__)
+
 #####
 # Check for missing system calls
 

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
@@ -1269,7 +1269,7 @@ static struct kcore_list kcore_vsyscall;
 
 static void __init register_page_bootmem_info(void)
 {
-#if defined(CONFIG_NUMA) || defined(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP)
+#if defined(CONFIG_NUMA) || defined(CONFIG_HUGETLB_PAGE_HAS_OPTIMIZE_VMEMMAP)
 	int i;
 
 	for_each_online_node(i)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
@@ -623,7 +623,7 @@ struct hstate {
 	unsigned int nr_huge_pages_node[MAX_NUMNODES];
 	unsigned int free_huge_pages_node[MAX_NUMNODES];
 	unsigned int surplus_huge_pages_node[MAX_NUMNODES];
-#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
+#ifdef CONFIG_HUGETLB_PAGE_HAS_OPTIMIZE_VMEMMAP
 	unsigned int optimize_vmemmap_pages;
 #endif
 #ifdef CONFIG_CGROUP_HUGETLB

diff --git a/include/linux/kconfig.h b/include/linux/kconfig.h
@@ -4,6 +4,10 @@
 
 #include <generated/autoconf.h>
 
+#ifndef __EXCLUDE_AUTOCONF_EXT_H
+#include <generated/autoconf_ext.h>
+#endif
+
 #ifdef CONFIG_CPU_BIG_ENDIAN
 #define __BIG_ENDIAN 4321
 #else

diff --git a/include/linux/mm.h b/include/linux/mm.h
@@ -3186,7 +3186,7 @@ static inline void print_vma_addr(char *prefix, unsigned long rip)
 }
 #endif
 
-#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
+#ifdef CONFIG_HUGETLB_PAGE_HAS_OPTIMIZE_VMEMMAP
 int vmemmap_remap_free(unsigned long start, unsigned long end,
 		       unsigned long reuse);
 int vmemmap_remap_alloc(unsigned long start, unsigned long end,

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
@@ -199,7 +199,7 @@ enum pageflags {
 
 #ifndef __GENERATING_BOUNDS_H
 
-#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
+#ifdef CONFIG_HUGETLB_PAGE_HAS_OPTIMIZE_VMEMMAP
 DECLARE_STATIC_KEY_MAYBE(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON,
 			 hugetlb_optimize_vmemmap_key);
 

diff --git a/kernel/autoconf_ext.c b/kernel/autoconf_ext.c
@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Generate definitions needed by the preprocessor.
+ * This code generates raw asm output which is post-processed
+ * to extract and format the required data.
+ */
+#include <linux/mm_types.h>
+#include <linux/kbuild.h>
+#include <linux/log2.h>
+
+int main(void)
+{
+	if (IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP) &&
+	    is_power_of_2(sizeof(struct page))) {
+		/*
+		 * The 2nd parameter of DEFINE() will go into the comments. Do
+		 * not pass 1 directly to it to make the generated macro more
+		 * clear for the readers.
+		 */
+		DEFINE(CONFIG_HUGETLB_PAGE_HAS_OPTIMIZE_VMEMMAP,
+		       IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP) &&
+		       is_power_of_2(sizeof(struct page)));
+	}
+
+	return 0;
+}
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
@@ -178,6 +178,7 @@
 
 #include "hugetlb_vmemmap.h"
 
+#ifdef CONFIG_HUGETLB_PAGE_HAS_OPTIMIZE_VMEMMAP
 /*
  * There are a lot of struct page structures associated with each HugeTLB page.
  * For tail pages, the value of compound_head is the same. So we can reuse first
@@ -194,12 +195,6 @@ EXPORT_SYMBOL(hugetlb_optimize_vmemmap_key);
 
 static int __init hugetlb_vmemmap_early_param(char *buf)
 {
-	/* We cannot optimize if a "struct page" crosses page boundaries. */
-	if (!is_power_of_2(sizeof(struct page))) {
-		pr_warn("cannot free vmemmap pages because \"struct page\" crosses page boundaries\n");
-		return 0;
-	}
-
 	if (!buf)
 		return -EINVAL;
 
@@ -300,3 +295,4 @@ void __init hugetlb_vmemmap_init(struct hstate *h)
 	pr_info("can optimize %d vmemmap pages for %s\n",
 		h->optimize_vmemmap_pages, h->name);
 }
+#endif /* CONFIG_HUGETLB_PAGE_HAS_OPTIMIZE_VMEMMAP */
diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
@@ -10,7 +10,7 @@
 #define _LINUX_HUGETLB_VMEMMAP_H
 #include <linux/hugetlb.h>
 
-#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
+#ifdef CONFIG_HUGETLB_PAGE_HAS_OPTIMIZE_VMEMMAP
 int hugetlb_vmemmap_alloc(struct hstate *h, struct page *head);
 void hugetlb_vmemmap_free(struct hstate *h, struct page *head);
 void hugetlb_vmemmap_init(struct hstate *h);
@@ -41,5 +41,5 @@ static inline unsigned int hugetlb_optimize_vmemmap_pages(struct hstate *h)
 {
 	return 0;
 }
-#endif /* CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP */
+#endif /* CONFIG_HUGETLB_PAGE_HAS_OPTIMIZE_VMEMMAP */
 #endif /* _LINUX_HUGETLB_VMEMMAP_H */
diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
@@ -34,7 +34,7 @@
 #include <asm/pgalloc.h>
 #include <asm/tlbflush.h>
 
-#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
+#ifdef CONFIG_HUGETLB_PAGE_HAS_OPTIMIZE_VMEMMAP
 /**
  * struct vmemmap_remap_walk - walk vmemmap page table
  *
@@ -420,7 +420,7 @@ int vmemmap_remap_alloc(unsigned long start, unsigned long end,
 
 	return 0;
 }
-#endif /* CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP */
+#endif /* CONFIG_HUGETLB_PAGE_HAS_OPTIMIZE_VMEMMAP */
 
 /*
  * Allocate a block of memory to be used to back the virtual memory map

diff --git a/scripts/mod/Makefile b/scripts/mod/Makefile
@@ -1,6 +1,8 @@
 # SPDX-License-Identifier: GPL-2.0
 OBJECT_FILES_NON_STANDARD := y
 CFLAGS_REMOVE_empty.o += $(CC_FLAGS_LTO)
+# See comments in Kbuild
+KBUILD_CFLAGS_KERNEL += -D__EXCLUDE_AUTOCONF_EXT_H
 
 hostprogs-always-y	+= modpost mk_elfconfig
 always-y		+= empty.o