[RFC PATCH 26/28] powerc/mm: try VMA lock-based page fault handling first

[Suren Baghdasaryan <surenb@google.com>]

From: Laurent Dufour <ldufour@linux.ibm.com>

Attempt VMA lock-based page fault handling first, and fall back to the
existing mmap_lock-based handling if that fails.
Copied from "x86/mm: try VMA lock-based page fault handling first"

Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
---
 arch/powerpc/mm/fault.c | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 014005428687..c92bdfcd1796 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -450,6 +450,44 @@ static int ___do_page_fault(struct pt_regs *regs, unsigned long address,
 	if (is_exec)
 		flags |= FAULT_FLAG_INSTRUCTION;
 
+#ifdef CONFIG_PER_VMA_LOCK
+	if (!(flags & FAULT_FLAG_USER) || atomic_read(&mm->mm_users) == 1)
+		goto lock_mmap;
+
+	vma = find_and_lock_anon_vma(mm, address);
+	if (!vma)
+		goto lock_mmap;
+
+	if (unlikely(access_pkey_error(is_write, is_exec,
+				       (error_code & DSISR_KEYFAULT), vma))) {
+		int rc = bad_access_pkey(regs, address, vma);
+
+		vma_read_unlock(vma);
+		return rc;
+	}
+
+	if (unlikely(access_error(is_write, is_exec, vma))) {
+		int rc = bad_access(regs, address);
+
+		vma_read_unlock(vma);
+		return rc;
+	}
+
+	fault = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, regs);
+	vma_read_unlock(vma);
+
+	if (!(fault & VM_FAULT_RETRY)) {
+		count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
+		goto done;
+	}
+	count_vm_vma_lock_event(VMA_LOCK_RETRY);
+
+	if (fault_signal_pending(fault, regs))
+		return user_mode(regs) ? 0 : SIGBUS;
+
+lock_mmap:
+#endif /* CONFIG_PER_VMA_LOCK */
+
 	/* When running in the kernel we expect faults to occur only to
 	 * addresses in user space.  All other faults represent errors in the
 	 * kernel and should generate an OOPS.  Unfortunately, in the case of an
@@ -526,6 +564,9 @@ static int ___do_page_fault(struct pt_regs *regs, unsigned long address,
 
 	mmap_read_unlock(current->mm);
 
+#ifdef CONFIG_PER_VMA_LOCK
+done:
+#endif
 	if (unlikely(fault & VM_FAULT_ERROR))
 		return mm_fault_error(regs, address, fault);
 
-- 
2.37.2.672.g94769d06f0-goog