[PATCH 2/4] powerpc/mm: Handle VDSO unmapping via close() rather than arch_unmap()

[Michael Ellerman <mpe@ellerman.id.au>]

Add a close() callback to the VDSO special mapping to handle unmapping
of the VDSO. That will make it possible to remove the arch_unmap() hook
entirely in a subsequent patch.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
 arch/powerpc/include/asm/mmu_context.h |  4 ----
 arch/powerpc/kernel/vdso.c             | 17 +++++++++++++++++
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
index 37bffa0f7918..9b8c1555744e 100644
--- a/arch/powerpc/include/asm/mmu_context.h
+++ b/arch/powerpc/include/asm/mmu_context.h
@@ -263,10 +263,6 @@ 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
diff --git a/arch/powerpc/kernel/vdso.c b/arch/powerpc/kernel/vdso.c
index 7a2ff9010f17..220a76cae7c1 100644
--- a/arch/powerpc/kernel/vdso.c
+++ b/arch/powerpc/kernel/vdso.c
@@ -81,6 +81,21 @@ static int vdso64_mremap(const struct vm_special_mapping *sm, struct vm_area_str
 	return vdso_mremap(sm, new_vma, &vdso64_end - &vdso64_start);
 }
 
+static void vdso_close(const struct vm_special_mapping *sm, struct vm_area_struct *vma)
+{
+	struct mm_struct *mm = vma->vm_mm;
+
+	/*
+	 * close() is called for munmap() but also for mremap(). In the mremap()
+	 * case the vdso pointer has already been updated by the mremap() hook
+	 * above, so it must not be set to NULL here.
+	 */
+	if (vma->vm_start != (unsigned long)mm->context.vdso)
+		return;
+
+	mm->context.vdso = NULL;
+}
+
 static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,
 			     struct vm_area_struct *vma, struct vm_fault *vmf);
 
@@ -92,11 +107,13 @@ static struct vm_special_mapping vvar_spec __ro_after_init = {
 static struct vm_special_mapping vdso32_spec __ro_after_init = {
 	.name = "[vdso]",
 	.mremap = vdso32_mremap,
+	.close = vdso_close,
 };
 
 static struct vm_special_mapping vdso64_spec __ro_after_init = {
 	.name = "[vdso]",
 	.mremap = vdso64_mremap,
+	.close = vdso_close,
 };
 
 #ifdef CONFIG_TIME_NS
-- 
2.45.2