[PATCH rfc -next 01/10] mm: add a generic VMA lock-based page fault handler

[Kefeng Wang]

There are more and more architectures enabled ARCH_SUPPORTS_PER_VMA_LOCK,
eg, x86, arm64, powerpc and s390, and riscv, those implementation are very
similar which results in some duplicated codes, let's add a generic VMA
lock-based page fault handler to eliminate them, and which also make it
easy to support this feature on new architectures.

Signed-off-by: Kefeng Wang <wangkefeng.wang at huawei.com>
---
 include/linux/mm.h | 28 ++++++++++++++++++++++++++++
 mm/memory.c        | 42 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 70 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index c7886784832b..cba1b7b19c9d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -633,6 +633,15 @@ static inline void vma_numab_state_init(struct vm_area_struct *vma) {}
 static inline void vma_numab_state_free(struct vm_area_struct *vma) {}
 #endif /* CONFIG_NUMA_BALANCING */
 
+struct vm_locked_fault {
+	struct mm_struct *mm;
+	unsigned long address;
+	unsigned int fault_flags;
+	unsigned long vm_flags;
+	struct pt_regs *regs;
+	unsigned long fault_code;
+};
+
 #ifdef CONFIG_PER_VMA_LOCK
 /*
  * Try to read-lock a vma. The function is allowed to occasionally yield false
@@ -733,6 +742,19 @@ static inline void assert_fault_locked(struct vm_fault *vmf)
 struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
 					  unsigned long address);
 
+#define VM_LOCKED_FAULT_INIT(_name, _mm, _address, _fault_flags, _vm_flags, _regs, _fault_code) \
+	_name.mm		= _mm;			\
+	_name.address		= _address;		\
+	_name.fault_flags	= _fault_flags;		\
+	_name.vm_flags		= _vm_flags;		\
+	_name.regs		= _regs;		\
+	_name.fault_code	= _fault_code
+
+int __weak arch_vma_check_access(struct vm_area_struct *vma,
+				 struct vm_locked_fault *vmlf);
+
+int try_vma_locked_page_fault(struct vm_locked_fault *vmlf, vm_fault_t *ret);
+
 #else /* CONFIG_PER_VMA_LOCK */
 
 static inline bool vma_start_read(struct vm_area_struct *vma)
@@ -742,6 +764,12 @@ static inline void vma_start_write(struct vm_area_struct *vma) {}
 static inline void vma_assert_write_locked(struct vm_area_struct *vma) {}
 static inline void vma_mark_detached(struct vm_area_struct *vma,
 				     bool detached) {}
+#define VM_LOCKED_FAULT_INIT(_name, _mm, _address, _fault_flags, _vm_flags, _regs, _fault_code)
+static inline int try_vma_locked_page_fault(struct vm_locked_fault *vmlf,
+					    vm_fault_t *ret)
+{
+	return -EINVAL;
+}
 
 static inline void release_fault_lock(struct vm_fault *vmf)
 {
diff --git a/mm/memory.c b/mm/memory.c
index ad790394963a..d3f5d1270e7a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5449,6 +5449,48 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
 	count_vm_vma_lock_event(VMA_LOCK_ABORT);
 	return NULL;
 }
+
+int __weak arch_vma_check_access(struct vm_area_struct *vma,
+				 struct vm_locked_fault *vmlf)
+{
+	if (!(vma->vm_flags & vmlf->vm_flags))
+		return -EINVAL;
+	return 0;
+}
+
+int try_vma_locked_page_fault(struct vm_locked_fault *vmlf, vm_fault_t *ret)
+{
+	struct vm_area_struct *vma;
+	vm_fault_t fault;
+
+	if (!(vmlf->fault_flags & FAULT_FLAG_USER))
+		return -EINVAL;
+
+	vma = lock_vma_under_rcu(vmlf->mm, vmlf->address);
+	if (!vma)
+		return -EINVAL;
+
+	if (arch_vma_check_access(vma, vmlf)) {
+		vma_end_read(vma);
+		return -EINVAL;
+	}
+
+	fault = handle_mm_fault(vma, vmlf->address,
+				vmlf->fault_flags | FAULT_FLAG_VMA_LOCK,
+				vmlf->regs);
+	*ret = fault;
+
+	if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))
+		vma_end_read(vma);
+
+	if ((fault & VM_FAULT_RETRY))
+		count_vm_vma_lock_event(VMA_LOCK_RETRY);
+	else
+		count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
+
+	return 0;
+}
+
 #endif /* CONFIG_PER_VMA_LOCK */
 
 #ifndef __PAGETABLE_P4D_FOLDED
-- 
2.27.0