um: Allocate vdso page pointer statically

Instead of dynamically allocating the pointer to the vdso page during
boot, we can just allocate it statically. Doing so will reduce error
handling and make the code slightly more readable.

Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20250212045756.164977-1-tiwei.btw@antgroup.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Author: btw616

arch/x86/um/vdso/vma.c

@@ -12,33 +12,22 @@
 
 static unsigned int __read_mostly vdso_enabled = 1;
 unsigned long um_vdso_addr;
+static struct page *um_vdso;
 
 extern unsigned long task_size;
 extern char vdso_start[], vdso_end[];
 
-static struct page **vdsop;
-
 static int __init init_vdso(void)
 {
-	struct page *um_vdso;
-
 	BUG_ON(vdso_end - vdso_start > PAGE_SIZE);
 
 	um_vdso_addr = task_size - PAGE_SIZE;
 
-	vdsop = kmalloc(sizeof(struct page *), GFP_KERNEL);
-	if (!vdsop)
-		goto oom;
-
 	um_vdso = alloc_page(GFP_KERNEL);
-	if (!um_vdso) {
-		kfree(vdsop);
-
+	if (!um_vdso)
 		goto oom;
-	}
 
 	copy_page(page_address(um_vdso), vdso_start);
-	*vdsop = um_vdso;
 
 	return 0;
 
@@ -56,6 +45,7 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 	struct mm_struct *mm = current->mm;
 	static struct vm_special_mapping vdso_mapping = {
 		.name = "[vdso]",
+		.pages = &um_vdso,
 	};
 
 	if (!vdso_enabled)
@@ -64,7 +54,6 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 	if (mmap_write_lock_killable(mm))
 		return -EINTR;
 
-	vdso_mapping.pages = vdsop;
 	vma = _install_special_mapping(mm, um_vdso_addr, PAGE_SIZE,
 		VM_READ|VM_EXEC|
 		VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,