ANDROID: 16K: Introduce pgsize_migration_inline.h

Introduce inline header to avoid circular dependency. This
will be used in a subsequent patch.

Also take opportunity to do some small noop refactor in
vma_pad_pages() and split_pad_vma() for more robust code.

Bug: 357901498
Change-Id: Ia5f447758d0d07ed3e1429ca1e35dcc0741cc22a
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>

include/linux/pgsize_migration.h

@@ -13,35 +13,9 @@
  * page size in Android.
  */
 
-#include <linux/mm.h>
+#include <linux/pgsize_migration_inline.h>
 #include <linux/seq_file.h>
-#include <linux/sizes.h>
+#include <linux/mm.h>
-
-/*
- * vm_flags representation of VMA padding pages.
- *
- * This allows the kernel to identify the portion of an ELF LOAD segment VMA
- * that is padding.
- *
- * 4 high bits of vm_flags [63,60] are used to represent ELF segment padding
- * up to 60kB, which is sufficient for ELFs of both 16kB and 64kB segment
- * alignment (p_align).
- *
- * The representation is illustrated below.
- *
- *                    63        62        61        60
- *                _________ _________ _________ _________
- *               |  Bit 3  |  Bit 2  |  Bit 1  |  Bit 0  |
- *               | of  4kB | of  4kB | of  4kB | of  4kB |
- *               |  chunks |  chunks |  chunks |  chunks |
- *               |_________|_________|_________|_________|
- */
-
-#define VM_PAD_WIDTH		4
-#define VM_PAD_SHIFT		(BITS_PER_LONG - VM_PAD_WIDTH)
-#define VM_TOTAL_PAD_PAGES	((1ULL << VM_PAD_WIDTH) - 1)
-#define VM_PAD_MASK		(VM_TOTAL_PAD_PAGES << VM_PAD_SHIFT)
-#define VMA_PAD_START(vma)	(vma->vm_end - (vma_pad_pages(vma) << PAGE_SHIFT))
 
 #if PAGE_SIZE == SZ_4K && defined(CONFIG_64BIT)
 extern void vma_set_pad_pages(struct vm_area_struct *vma,
@@ -63,9 +37,6 @@ extern void show_map_pad_vma(struct vm_area_struct *vma,
 extern void split_pad_vma(struct vm_area_struct *vma, struct vm_area_struct *new,
 			  unsigned long addr, int new_below);
 
-extern unsigned long vma_pad_fixup_flags(struct vm_area_struct *vma,
-					 unsigned long newflags);
-
 extern bool is_mergable_pad_vma(struct vm_area_struct *vma,
 				unsigned long vm_flags);
 
@@ -107,12 +78,6 @@ static inline void split_pad_vma(struct vm_area_struct *vma, struct vm_area_stru
 {
 }
 
-static inline unsigned long vma_pad_fixup_flags(struct vm_area_struct *vma,
-						unsigned long newflags)
-{
-	return newflags;
-}
-
 static inline bool is_mergable_pad_vma(struct vm_area_struct *vma,
 				       unsigned long vm_flags)
 {

include/linux/pgsize_migration_inline.h

@@ -0,0 +1,67 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_PAGE_SIZE_MIGRATION_INLINE_H
+#define _LINUX_PAGE_SIZE_MIGRATION_INLINE_H
+
+/*
+ * Page Size Migration
+ *
+ * Copyright (c) 2024, Google LLC.
+ * Author: Kalesh Singh <kaleshsingh@goole.com>
+ *
+ * This file contains inline APIs for mitigations to ensure
+ * app compatibility during the transition from 4kB to 16kB
+ * page size in Android.
+ */
+
+#include <linux/mm_types.h>
+#include <linux/sizes.h>
+
+#include <asm/page.h>
+
+/*
+ * vm_flags representation of VMA padding pages.
+ *
+ * This allows the kernel to identify the portion of an ELF LOAD segment VMA
+ * that is padding.
+ *
+ * 4 high bits of vm_flags [63,60] are used to represent ELF segment padding
+ * up to 60kB, which is sufficient for ELFs of both 16kB and 64kB segment
+ * alignment (p_align).
+ *
+ * The representation is illustrated below.
+ *
+ *                    63        62        61        60
+ *                _________ _________ _________ _________
+ *               |  Bit 3  |  Bit 2  |  Bit 1  |  Bit 0  |
+ *               | of  4kB | of  4kB | of  4kB | of  4kB |
+ *               |  chunks |  chunks |  chunks |  chunks |
+ *               |_________|_________|_________|_________|
+ */
+
+#define VM_PAD_WIDTH		4
+#define VM_PAD_SHIFT		(BITS_PER_LONG - VM_PAD_WIDTH)
+#define VM_TOTAL_PAD_PAGES	((1ULL << VM_PAD_WIDTH) - 1)
+#define VM_PAD_MASK		(VM_TOTAL_PAD_PAGES << VM_PAD_SHIFT)
+#define VMA_PAD_START(vma)	(vma->vm_end - (vma_pad_pages(vma) << PAGE_SHIFT))
+
+#if PAGE_SIZE == SZ_4K && defined(CONFIG_64BIT)
+/*
+ * Sets the correct padding bits / flags for a VMA split.
+ */
+static inline unsigned long vma_pad_fixup_flags(struct vm_area_struct *vma,
+						unsigned long newflags)
+{
+	if (newflags & VM_PAD_MASK)
+		return (newflags & ~VM_PAD_MASK) | (vma->vm_flags & VM_PAD_MASK);
+	else
+		return newflags;
+}
+#else /* PAGE_SIZE != SZ_4K || !defined(CONFIG_64BIT) */
+static inline unsigned long vma_pad_fixup_flags(struct vm_area_struct *vma,
+						unsigned long newflags)
+{
+	return newflags;
+}
+#endif /* PAGE_SIZE == SZ_4K && defined(CONFIG_64BIT) */
+
+#endif /* _LINUX_PAGE_SIZE_MIGRATION_INLINE_H */

mm/pgsize_migration.c

@@ -126,7 +126,7 @@ unsigned long vma_pad_pages(struct vm_area_struct *vma)
 	if (!is_pgsize_migration_enabled())
 		return 0;
 
-	return vma->vm_flags >> VM_PAD_SHIFT;
+	return (vma->vm_flags & VM_PAD_MASK) >> VM_PAD_SHIFT;
 }
 
 static __always_inline bool str_has_suffix(const char *str, const char *suffix)
@@ -397,7 +397,7 @@ void split_pad_vma(struct vm_area_struct *vma, struct vm_area_struct *new,
 	nr_vma2_pages = vma_pages(second);
 
 	if (nr_vma2_pages >= nr_pad_pages) { 			/* Case 1 & 3 */
-		first->vm_flags &= ~VM_PAD_MASK;
+		vma_set_pad_pages(first, 0);
 		vma_set_pad_pages(second, nr_pad_pages);
 	} else {						/* Case 2 */
 		vma_set_pad_pages(first, nr_pad_pages - nr_vma2_pages);
@@ -405,18 +405,6 @@ void split_pad_vma(struct vm_area_struct *vma, struct vm_area_struct *new,
 	}
 }
 
-/*
- * Sets the correct padding bits / flags for a VMA split.
- */
-unsigned long vma_pad_fixup_flags(struct vm_area_struct *vma,
-				  unsigned long newflags)
-{
-	if (newflags & VM_PAD_MASK)
-		return (newflags & ~VM_PAD_MASK) | (vma->vm_flags & VM_PAD_MASK);
-	else
-		return newflags;
-}
-
 /*
  * Merging of padding VMAs is uncommon, as padding is only allowed
  * from the linker context.