[RFC PATCH 15/24] x86 fault handler: use a pseudo-vma when operating on anonymous vmas.

[Michel Lespinasse <walken@google.com>]

Update the fault handler to use a pseudo-vma when the original vma is
anonymous. This is in preparation to handling such faults with a fine
grained range lock in a later change.

Signed-off-by: Michel Lespinasse <walken@google.com>
---
 arch/x86/mm/fault.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git arch/x86/mm/fault.c arch/x86/mm/fault.c
index 700da3cc3db9..52333272e14e 100644
--- arch/x86/mm/fault.c
+++ arch/x86/mm/fault.c
@@ -1279,7 +1279,7 @@ void do_user_addr_fault(struct pt_regs *regs,
 			unsigned long address)
 {
 	struct mm_lock_range *range;
-	struct vm_area_struct *vma;
+	struct vm_area_struct pvma, *vma;
 	struct task_struct *tsk;
 	struct mm_struct *mm;
 	vm_fault_t fault, major = 0;
@@ -1423,6 +1423,23 @@ void do_user_addr_fault(struct pt_regs *regs,
 		return;
 	}
 
+	if (vma_is_anonymous(vma)) {
+		/*
+		 * Allocate anon_vma if needed.
+		 * This needs to operate on the vma of record.
+		 */
+		fault = prepare_mm_fault(vma, flags);
+		if (fault)
+			goto got_fault;
+
+		/*
+		 * Copy vma attributes into a pseudo-vma.
+		 * This will be required when using fine grained locks.
+		 */
+		pvma = *vma;
+		vma = &pvma;
+	}
+
 	/*
 	 * If for any reason at all we couldn't handle the fault,
 	 * make sure we exit gracefully rather than endlessly redo
@@ -1437,6 +1454,7 @@ void do_user_addr_fault(struct pt_regs *regs,
 	 * FAULT_FLAG_USER|FAULT_FLAG_KILLABLE are both set in flags.
 	 */
 	fault = handle_mm_fault_range(vma, address, flags, range);
+got_fault:
 	major |= fault & VM_FAULT_MAJOR;
 
 	/*
-- 
2.25.0.341.g760bfbb309-goog