mm: remove CONFIG_PER_VMA_LOCK ifdefs

Patch series "Handle most file-backed faults under the VMA lock", v3.

This patchset adds the ability to handle page faults on parts of files
which are already in the page cache without taking the mmap lock.


This patch (of 10):

Provide lock_vma_under_rcu() when CONFIG_PER_VMA_LOCK is not defined to
eliminate ifdefs in the users.

Link: https://lkml.kernel.org/r/20230724185410.1124082-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20230724185410.1124082-2-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Cc: Punit Agrawal <punit.agrawal@bytedance.com>
Cc: Arjun Roy <arjunroy@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/arm64/mm/fault.c

@@ -587,7 +587,6 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
 
 	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
 
-#ifdef CONFIG_PER_VMA_LOCK
 	if (!(mm_flags & FAULT_FLAG_USER))
 		goto lock_mmap;
 
@@ -615,7 +614,6 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
 		return 0;
 	}
 lock_mmap:
-#endif /* CONFIG_PER_VMA_LOCK */
 
 retry:
 	vma = lock_mm_and_find_vma(mm, addr, regs);

arch/powerpc/mm/fault.c

@@ -469,7 +469,6 @@ 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;
 
@@ -501,7 +500,6 @@ static int ___do_page_fault(struct pt_regs *regs, unsigned long address,
 		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
@@ -551,9 +549,7 @@ 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/riscv/mm/fault.c

@@ -283,7 +283,6 @@ void handle_page_fault(struct pt_regs *regs)
 		flags |= FAULT_FLAG_WRITE;
 	else if (cause == EXC_INST_PAGE_FAULT)
 		flags |= FAULT_FLAG_INSTRUCTION;
-#ifdef CONFIG_PER_VMA_LOCK
 	if (!(flags & FAULT_FLAG_USER))
 		goto lock_mmap;
 
@@ -311,7 +310,6 @@ void handle_page_fault(struct pt_regs *regs)
 		return;
 	}
 lock_mmap:
-#endif /* CONFIG_PER_VMA_LOCK */
 
 retry:
 	vma = lock_mm_and_find_vma(mm, addr, regs);
@@ -368,9 +366,7 @@ void handle_page_fault(struct pt_regs *regs)
 
 	mmap_read_unlock(mm);
 
-#ifdef CONFIG_PER_VMA_LOCK
 done:
-#endif
 	if (unlikely(fault & VM_FAULT_ERROR)) {
 		tsk->thread.bad_cause = cause;
 		mm_fault_error(regs, addr, fault);

arch/s390/mm/fault.c

@@ -407,7 +407,6 @@ 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);
@@ -432,7 +431,6 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
 		goto out;
 	}
 lock_mmap:
-#endif /* CONFIG_PER_VMA_LOCK */
 	mmap_read_lock(mm);
 
 	gmap = NULL;

arch/x86/mm/fault.c

@@ -1328,7 +1328,6 @@ void do_user_addr_fault(struct pt_regs *regs,
 	}
 #endif
 
-#ifdef CONFIG_PER_VMA_LOCK
 	if (!(flags & FAULT_FLAG_USER))
 		goto lock_mmap;
 
@@ -1358,7 +1357,6 @@ void do_user_addr_fault(struct pt_regs *regs,
 		return;
 	}
 lock_mmap:
-#endif /* CONFIG_PER_VMA_LOCK */
 
 retry:
 	vma = lock_mm_and_find_vma(mm, address, regs);
@@ -1418,9 +1416,7 @@ void do_user_addr_fault(struct pt_regs *regs,
 	}
 
 	mmap_read_unlock(mm);
-#ifdef CONFIG_PER_VMA_LOCK
 done:
-#endif
 	if (likely(!(fault & VM_FAULT_ERROR)))
 		return;
 

include/linux/mm.h

@@ -742,6 +742,12 @@ 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) {}
 
+static inline struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
+		unsigned long address)
+{
+	return NULL;
+}
+
 #endif /* CONFIG_PER_VMA_LOCK */
 
 /*