[PATCH mm-unstable v2 02/16] mm: x86: Introduce arch_mmap_hint()

[Kalesh Singh]

Introduce x86 arch_mmap_hint() and define HAVE_ARCH_MMAP_HINT.
This is a preparatory patch, no functional change is introduced.

Fallback to generic_mmap_hint() if an architecture doesn't
provide HAVE_ARCH_MMAP_HINT.

Signed-off-by: Kalesh Singh <kaleshsingh at google.com>
---

Changes in v2:
  - MAP_FIXED case is also handled in arch_mmap_hint() since this is just a
    special case of the hint addr being "enforced", per Yang Shi.
  - Consolidate most of the error handling in arch_mmap_hint().
  - Fallback to generic_mmap_hint() if arch_mmap_hint() is not provided.

 arch/x86/include/asm/pgtable_64.h |  1 +
 arch/x86/kernel/sys_x86_64.c      | 64 +++++++++++++++----------------
 include/linux/sched/mm.h          |  5 +++
 mm/mmap.c                         |  9 +++++
 4 files changed, 45 insertions(+), 34 deletions(-)

diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h
index d1426b64c1b9..4472fd0040c3 100644
--- a/arch/x86/include/asm/pgtable_64.h
+++ b/arch/x86/include/asm/pgtable_64.h
@@ -245,6 +245,7 @@ extern void cleanup_highmap(void);
 
 #define HAVE_ARCH_UNMAPPED_AREA
 #define HAVE_ARCH_UNMAPPED_AREA_TOPDOWN
+#define HAVE_ARCH_MMAP_HINT
 
 #define PAGE_AGP    PAGE_KERNEL_NOCACHE
 #define HAVE_PAGE_AGP 1
diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c
index 776ae6fa7f2d..008c6d19bd02 100644
--- a/arch/x86/kernel/sys_x86_64.c
+++ b/arch/x86/kernel/sys_x86_64.c
@@ -123,31 +123,44 @@ static inline unsigned long stack_guard_placement(vm_flags_t vm_flags)
 	return 0;
 }
 
+unsigned long arch_mmap_hint(struct file *filp, unsigned long addr,
+			     unsigned long len, unsigned long pgoff,
+			     unsigned long flags)
+{
+	unsigned long begin, end;
+
+	find_start_end(addr, flags, &begin, &end);
+
+	/* requested length too big for entire address space */
+	if (len > end || len > TASK_SIZE)
+		return -ENOMEM;
+
+	/* No address checking. See comment at mmap_address_hint_valid() */
+	if (flags & MAP_FIXED)
+		return addr;
+
+	addr = PAGE_ALIGN(addr);
+
+	/* Fallback to VA space search? */
+	if (!mmap_address_hint_valid(addr, len))
+		return 0;
+
+	return generic_mmap_hint(filp, addr, len, pgoff, flags);
+}
+
 unsigned long
 arch_get_unmapped_area(struct file *filp, unsigned long addr, unsigned long len,
 		       unsigned long pgoff, unsigned long flags, vm_flags_t vm_flags)
 {
-	struct mm_struct *mm = current->mm;
-	struct vm_area_struct *vma;
 	struct vm_unmapped_area_info info = {};
 	unsigned long begin, end;
 
-	if (flags & MAP_FIXED)
+	addr = arch_mmap_hint(filp, addr, len, pgoff, flags);
+	if (addr)
 		return addr;
 
 	find_start_end(addr, flags, &begin, &end);
 
-	if (len > end)
-		return -ENOMEM;
-
-	if (addr) {
-		addr = PAGE_ALIGN(addr);
-		vma = find_vma(mm, addr);
-		if (end - len >= addr &&
-		    (!vma || addr + len <= vm_start_gap(vma)))
-			return addr;
-	}
-
 	info.length = len;
 	info.low_limit = begin;
 	info.high_limit = end;
@@ -168,34 +181,17 @@ arch_get_unmapped_area_topdown(struct file *filp, unsigned long addr0,
 			  unsigned long len, unsigned long pgoff,
 			  unsigned long flags, vm_flags_t vm_flags)
 {
-	struct vm_area_struct *vma;
-	struct mm_struct *mm = current->mm;
 	unsigned long addr = addr0;
 	struct vm_unmapped_area_info info = {};
 
-	/* requested length too big for entire address space */
-	if (len > TASK_SIZE)
-		return -ENOMEM;
-
-	/* No address checking. See comment at mmap_address_hint_valid() */
-	if (flags & MAP_FIXED)
-		return addr;
-
 	/* for MAP_32BIT mappings we force the legacy mmap base */
 	if (!in_32bit_syscall() && (flags & MAP_32BIT))
 		goto bottomup;
 
 	/* requesting a specific address */
-	if (addr) {
-		addr &= PAGE_MASK;
-		if (!mmap_address_hint_valid(addr, len))
-			goto get_unmapped_area;
-
-		vma = find_vma(mm, addr);
-		if (!vma || addr + len <= vm_start_gap(vma))
-			return addr;
-	}
-get_unmapped_area:
+	addr = arch_mmap_hint(filp, addr, len, pgoff, flags);
+	if (addr)
+		return addr;
 
 	info.flags = VM_UNMAPPED_AREA_TOPDOWN;
 	info.length = len;
diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index edeec19d1708..f4143703f234 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -205,6 +205,11 @@ unsigned long generic_mmap_hint(struct file *filp, unsigned long addr,
 				unsigned long len, unsigned long pgoff,
 				unsigned long flags);
 
+/* See generic_mmap_hint() */
+unsigned long arch_mmap_hint(struct file *filp, unsigned long addr,
+			     unsigned long len, unsigned long pgoff,
+			     unsigned long flags);
+
 unsigned long
 generic_get_unmapped_area(struct file *filp, unsigned long addr,
 			  unsigned long len, unsigned long pgoff,
diff --git a/mm/mmap.c b/mm/mmap.c
index 382b4eac5406..76dd6acdf051 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -705,6 +705,15 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
 }
 #endif
 
+#ifndef HAVE_ARCH_MMAP_HINT
+unsigned long arch_mmap_hint(struct file *filp, unsigned long addr,
+				      unsigned long len, unsigned long pgoff,
+				      unsigned long flags)
+{
+	return generic_mmap_hint(filp, addr, len, pgoff, flags);
+}
+#endif
+
 /*
  * This mmap-allocator allocates new areas top-down from below the
  * stack's low limit (the base):
-- 
2.47.0.338.g60cca15819-goog