Although, time namespace can work with VVAR VMA split, it seems worth
to forbid splitting VVAR resulting in stricter ABI and reducing amount
of corner-cases to consider while working further on VDSO.

I don't think there is any use-case for partial mremap() of vvar,
but if there is any - this patch can be easily reverted.

Co-developed-by: Andrei Vagin <ava...@openvz.org>
Signed-off-by: Andrei Vagin <ava...@openvz.org>
Signed-off-by: Dmitry Safonov <d...@arista.com>
---
 arch/x86/entry/vdso/vma.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index 349a61d8bf34..3f05418642a8 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -84,6 +84,18 @@ static int vdso_mremap(const struct vm_special_mapping *sm,
        return 0;
 }
 
+static int vvar_mremap(const struct vm_special_mapping *sm,
+               struct vm_area_struct *new_vma)
+{
+       unsigned long new_size = new_vma->vm_end - new_vma->vm_start;
+       const struct vdso_image *image = new_vma->vm_mm->context.vdso_image;
+
+       if (new_size != -image->sym_vvar_start)
+               return -EINVAL;
+
+       return 0;
+}
+
 static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,
                      struct vm_area_struct *vma, struct vm_fault *vmf)
 {
@@ -136,6 +148,7 @@ static const struct vm_special_mapping vdso_mapping = {
 static const struct vm_special_mapping vvar_mapping = {
        .name = "[vvar]",
        .fault = vvar_fault,
+       .mremap = vvar_mremap,
 };
 
 /*
-- 
2.22.0

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