[PATCH v4 17/21] mm/mmap: Drop arch_unmap() call from all archs

["Liam R. Howlett" <Liam.Howlett@oracle.com>]

From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>

The arch_unmap call was previously moved above the rbtree modifications
in commit 5a28fc94c914 ("x86/mpx, mm/core: Fix recursive munmap()
corruption").  The move was motivated by an issue with calling
arch_unmap() after the rbtree was modified.

Since the above commit, mpx was dropped from the kernel in 45fc24e89b7c
("x86/mpx: remove MPX from arch/x86"), so the motivation for calling
arch_unmap() prior to modifying the vma tree no longer exists
(regardless of rbtree or maple tree implementations).

Furthermore, the powerpc implementation is also no longer needed as per
[1] and [2].  So the arch_unmap() function can be completely removed.

Link: https://lore.kernel.org/lkml/20210611180242.711399-1-dima@arista.com/
Link: https://github.com/linuxppc/issues/issues/241
Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: LEROY Christophe <christophe.leroy2@cs-soprasteria.com>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Dmitry Safonov <dima@arista.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
---
 arch/powerpc/include/asm/mmu_context.h |  9 ---------
 arch/x86/include/asm/mmu_context.h     |  5 -----
 include/asm-generic/mm_hooks.h         | 11 +++--------
 mm/mmap.c                              | 12 ++----------
 4 files changed, 5 insertions(+), 32 deletions(-)

diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
index 37bffa0f7918..a334a1368848 100644
--- a/arch/powerpc/include/asm/mmu_context.h
+++ b/arch/powerpc/include/asm/mmu_context.h
@@ -260,15 +260,6 @@ static inline void enter_lazy_tlb(struct mm_struct *mm,
 
 extern void arch_exit_mmap(struct mm_struct *mm);
 
-static inline void arch_unmap(struct mm_struct *mm,
-			      unsigned long start, unsigned long end)
-{
-	unsigned long vdso_base = (unsigned long)mm->context.vdso;
-
-	if (start <= vdso_base && vdso_base < end)
-		mm->context.vdso = NULL;
-}
-
 #ifdef CONFIG_PPC_MEM_KEYS
 bool arch_vma_access_permitted(struct vm_area_struct *vma, bool write,
 			       bool execute, bool foreign);
diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index 8dac45a2c7fc..80f2a3187aa6 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -232,11 +232,6 @@ static inline bool is_64bit_mm(struct mm_struct *mm)
 }
 #endif
 
-static inline void arch_unmap(struct mm_struct *mm, unsigned long start,
-			      unsigned long end)
-{
-}
-
 /*
  * We only want to enforce protection keys on the current process
  * because we effectively have no access to PKRU for other
diff --git a/include/asm-generic/mm_hooks.h b/include/asm-generic/mm_hooks.h
index 4dbb177d1150..f7996376baf9 100644
--- a/include/asm-generic/mm_hooks.h
+++ b/include/asm-generic/mm_hooks.h
@@ -1,8 +1,8 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /*
- * Define generic no-op hooks for arch_dup_mmap, arch_exit_mmap
- * and arch_unmap to be included in asm-FOO/mmu_context.h for any
- * arch FOO which doesn't need to hook these.
+ * Define generic no-op hooks for arch_dup_mmap and arch_exit_mmap to be
+ * included in asm-FOO/mmu_context.h for any arch FOO which doesn't need to hook
+ * these.
  */
 #ifndef _ASM_GENERIC_MM_HOOKS_H
 #define _ASM_GENERIC_MM_HOOKS_H
@@ -17,11 +17,6 @@ static inline void arch_exit_mmap(struct mm_struct *mm)
 {
 }
 
-static inline void arch_unmap(struct mm_struct *mm,
-			unsigned long start, unsigned long end)
-{
-}
-
 static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
 		bool write, bool execute, bool foreign)
 {
diff --git a/mm/mmap.c b/mm/mmap.c
index d5bd404893a8..df565f51971d 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2652,6 +2652,7 @@ static void vms_complete_munmap_vmas(struct vma_munmap_struct *vms,
 	mm = vms->mm;
 	mm->map_count -= vms->vma_count;
 	mm->locked_vm -= vms->locked_vm;
+
 	if (vms->unlock)
 		mmap_write_downgrade(mm);
 
@@ -2879,7 +2880,7 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
  *
  * This function takes a @mas that is either pointing to the previous VMA or set
  * to MA_START and sets it up to remove the mapping(s).  The @len will be
- * aligned and any arch_unmap work will be preformed.
+ * aligned.
  *
  * Return: 0 on success and drops the lock if so directed, error and leaves the
  * lock held otherwise.
@@ -2899,16 +2900,12 @@ int do_vmi_munmap(struct vma_iterator *vmi, struct mm_struct *mm,
 		return -EINVAL;
 
 	/*
-	 * Check if memory is sealed before arch_unmap.
 	 * Prevent unmapping a sealed VMA.
 	 * can_modify_mm assumes we have acquired the lock on MM.
 	 */
 	if (unlikely(!can_modify_mm(mm, start, end)))
 		return -EPERM;
 
-	 /* arch_unmap() might do unmaps itself.  */
-	arch_unmap(mm, start, end);
-
 	/* Find the first overlapping VMA */
 	vma = vma_find(vmi, end);
 	if (!vma) {
@@ -2969,9 +2966,6 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 	if (unlikely(!can_modify_mm(mm, addr, end)))
 		return -EPERM;
 
-	 /* arch_unmap() might do unmaps itself.  */
-	arch_unmap(mm, addr, end);
-
 	/* Find the first overlapping VMA */
 	vma = vma_find(&vmi, end);
 	init_vma_munmap(&vms, &vmi, vma, addr, end, uf, /* unlock = */ false);
@@ -3348,14 +3342,12 @@ int do_vma_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
 	struct mm_struct *mm = vma->vm_mm;
 
 	/*
-	 * Check if memory is sealed before arch_unmap.
 	 * Prevent unmapping a sealed VMA.
 	 * can_modify_mm assumes we have acquired the lock on MM.
 	 */
 	if (unlikely(!can_modify_mm(mm, start, end)))
 		return -EPERM;
 
-	arch_unmap(mm, start, end);
 	return do_vmi_align_munmap(vmi, vma, mm, start, end, uf, unlock);
 }
 
-- 
2.43.0