[PATCH -next] s390/mm: try VMA lock-based page fault handling first

[Heiko Carstens]

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".

Signed-off-by: Heiko Carstens <hca@xxxxxxxxxxxxx>
---
 arch/s390/Kconfig    |  1 +
 arch/s390/mm/fault.c | 24 ++++++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 9809c74e1240..548b5b587003 100644
--- a/arch/s390/Kconfig
+++ b/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
diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index a2632fd97d00..b65144c392b0 100644
--- a/arch/s390/mm/fault.c
+++ b/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;
-- 
2.37.2