userswap: convert enable_userswap to static key

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I6CAIM

--------------------------------

Replace enable_userswap with struct static_key_false userswap_enabled.
Signed-off-by: NZhangPeng <zhangpeng362@huawei.com>

include/linux/userswap.h

@@ -11,7 +11,7 @@
 
 #ifdef CONFIG_USERSWAP
 
-extern int enable_userswap;
+extern struct static_key_false userswap_enabled;
 
 /*
  * In uswap situation, we use the bit 0 of the returned address to indicate
@@ -43,7 +43,7 @@ static inline bool uswap_check_copy_mode(struct vm_area_struct *vma, __u64 mode)
 
 static inline bool uswap_validate_mremap_flags(unsigned long flags)
 {
-	if (!enable_userswap && flags & MREMAP_USWAP_SET_PTE)
+	if (!static_branch_unlikely(&userswap_enabled) && flags & MREMAP_USWAP_SET_PTE)
 		return false;
 	if (flags & MREMAP_USWAP_SET_PTE && flags & ~MREMAP_USWAP_SET_PTE)
 		return false;
@@ -80,7 +80,7 @@ static inline void uswap_get_cpu_id(unsigned long reason, struct uffd_msg *msg)
 
 static inline void uswap_release(unsigned long *userfault_flags)
 {
-	if (enable_userswap)
+	if (static_branch_unlikely(&userswap_enabled))
 		*userfault_flags |= VM_USWAP;
 }
 

mm/userfaultfd.c

@@ -586,7 +586,8 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
 		BUG_ON(pmd_trans_huge(*dst_pmd));
 
 #ifdef CONFIG_USERSWAP
-		if (dst_vma->vm_flags & VM_USWAP &&
+		if (static_branch_unlikely(&userswap_enabled) &&
+		    dst_vma->vm_flags & VM_USWAP &&
 		    mode & UFFDIO_COPY_MODE_DIRECT_MAP)
 			err = mfill_atomic_pte_nocopy(dst_mm, dst_pmd, dst_vma,
 						      dst_addr, src_addr);

mm/userswap.c

@@ -14,7 +14,7 @@
 
 #include "internal.h"
 
-int enable_userswap;
+DEFINE_STATIC_KEY_FALSE(userswap_enabled);
 
 static bool vma_uswap_compatible(struct vm_area_struct *vma)
 {
@@ -470,7 +470,7 @@ bool uswap_register(struct uffdio_register *uffdio_register,
 	struct vm_area_struct *vma;
 	unsigned long end;
 
-	if (!enable_userswap)
+	if (!static_branch_unlikely(&userswap_enabled))
 		return true;
 	if (!(uffdio_register->mode & UFFDIO_REGISTER_MODE_USWAP))
 		return true;
@@ -496,6 +496,9 @@ bool uswap_register(struct uffdio_register *uffdio_register,
 bool do_uswap_page(swp_entry_t entry, struct vm_fault *vmf,
 		   struct vm_area_struct *vma, vm_fault_t *ret)
 {
+	if (!static_branch_unlikely(&userswap_enabled))
+		return true;
+
 	if (swp_type(entry) != SWP_USERSWAP_ENTRY)
 		return true;
 
@@ -519,7 +522,7 @@ bool do_uswap_page(swp_entry_t entry, struct vm_fault *vmf,
 
 static int __init enable_userswap_setup(char *str)
 {
-	enable_userswap = true;
+	static_branch_enable(&userswap_enabled);
 	return 1;
 }
 __setup("enable_userswap", enable_userswap_setup);