powerc/mm: try VMA lock-based page fault handling first

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"

[ldufour@linux.ibm.com: powerpc/mm: fix mmap_lock bad unlock]
  Link: https://lkml.kernel.org/r/20230306154244.17560-1-ldufour@linux.ibm.com
  Link: https://lore.kernel.org/linux-mm/842502FB-F99C-417C-9648-A37D0ECDC9CE@linux.ibm.com
Link: https://lkml.kernel.org/r/20230227173632.3292573-32-surenb@google.com
Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Cc: Sachin Sant <sachinp@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: ldu4

arch/powerpc/mm/fault.c

@@ -474,6 +474,40 @@ 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))
+		goto lock_mmap;
+
+	vma = lock_vma_under_rcu(mm, address);
+	if (!vma)
+		goto lock_mmap;
+
+	if (unlikely(access_pkey_error(is_write, is_exec,
+				       (error_code & DSISR_KEYFAULT), vma))) {
+		vma_end_read(vma);
+		goto lock_mmap;
+	}
+
+	if (unlikely(access_error(is_write, is_exec, vma))) {
+		vma_end_read(vma);
+		goto lock_mmap;
+	}
+
+	fault = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, regs);
+	vma_end_read(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
@@ -550,6 +584,9 @@ 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);
 

arch/powerpc/platforms/powernv/Kconfig

@@ -16,6 +16,7 @@ config PPC_POWERNV
 	select PPC_DOORBELL
 	select MMU_NOTIFIER
 	select FORCE_SMP
+	select ARCH_SUPPORTS_PER_VMA_LOCK
 	default y
 
 config OPAL_PRD

arch/powerpc/platforms/pseries/Kconfig

@@ -22,6 +22,7 @@ config PPC_PSERIES
 	select HOTPLUG_CPU
 	select FORCE_SMP
 	select SWIOTLB
+	select ARCH_SUPPORTS_PER_VMA_LOCK
 	default y
 
 config PARAVIRT