s390/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.

This is the s390 variant of "x86/mm: try VMA lock-based page fault handling
first".

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Heiko Carstens <[email protected]>
Cc: Alexander Gordeev <[email protected]>
Cc: Christian Borntraeger <[email protected]>
Cc: Gerald Schaefer <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Sven Schnelle <[email protected]>
Cc: Vasily Gorbik <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: hcahca

arch/s390/Kconfig

@@ -120,6 +120,7 @@ config S390
 	select ARCH_SUPPORTS_DEBUG_PAGEALLOC
 	select ARCH_SUPPORTS_HUGETLBFS
 	select ARCH_SUPPORTS_NUMA_BALANCING
+	select ARCH_SUPPORTS_PER_VMA_LOCK
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_CMPXCHG_LOCKREF
 	select ARCH_WANTS_DYNAMIC_TASK_STRUCT

arch/s390/mm/fault.c

@@ -407,6 +407,30 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
 		access = VM_WRITE;
 	if (access == VM_WRITE)
 		flags |= FAULT_FLAG_WRITE;
+#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 (!(vma->vm_flags & access)) {
+		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 out;
+	}
+	count_vm_vma_lock_event(VMA_LOCK_RETRY);
+	/* Quick path to respond to signals */
+	if (fault_signal_pending(fault, regs)) {
+		fault = VM_FAULT_SIGNAL;
+		goto out;
+	}
+lock_mmap:
+#endif /* CONFIG_PER_VMA_LOCK */
 	mmap_read_lock(mm);
 
 	gmap = NULL;