ARM: 7294/1: vectors: use gate_vma for vectors user mapping

The current user mapping for the vectors page is inserted as a `horrible
hack vma' into each task via arch_setup_additional_pages. This causes
problems with the MM subsystem and vm_normal_page, as described here:

https://lkml.org/lkml/2012/1/14/55

Following the suggestion from Hugh in the above thread, this patch uses
the gate_vma for the vectors user mapping, therefore consolidating
the horrible hack VMAs into one.

Acked-and-Tested-by: Nicolas Pitre <nico@linaro.org>

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 28 insertions, 10 deletions

diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 971d65c253a9..e11b523db332 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -526,22 +526,40 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
 #ifdef CONFIG_MMU
 /*
  * The vectors page is always readable from user space for the
- * atomic helpers and the signal restart code.  Let's declare a mapping
- * for it so it is visible through ptrace and /proc/<pid>/mem.
+ * atomic helpers and the signal restart code. Insert it into the
+ * gate_vma so that it is visible through ptrace and /proc/<pid>/mem.
  */
+static struct vm_area_struct gate_vma;
 
-int vectors_user_mapping(void)
+static int __init gate_vma_init(void)
 {
-        struct mm_struct *mm = current->mm;
-        return install_special_mapping(mm, 0xffff0000, PAGE_SIZE,
-                                       VM_READ | VM_EXEC |
-                                       VM_MAYREAD | VM_MAYEXEC |
-                                       VM_ALWAYSDUMP | VM_RESERVED,
-                                       NULL);
+        gate_vma.vm_start       = 0xffff0000;
+        gate_vma.vm_end         = 0xffff0000 + PAGE_SIZE;
+        gate_vma.vm_page_prot   = PAGE_READONLY_EXEC;
+        gate_vma.vm_flags       = VM_READ | VM_EXEC |
+                                  VM_MAYREAD | VM_MAYEXEC |
+                                  VM_ALWAYSDUMP;
+        return 0;
+}
+arch_initcall(gate_vma_init);
+
+struct vm_area_struct *get_gate_vma(struct mm_struct *mm)
+{
+        return &gate_vma;
+}
+
+int in_gate_area(struct mm_struct *mm, unsigned long addr)
+{
+        return (addr >= gate_vma.vm_start) && (addr < gate_vma.vm_end);
+}
+
+int in_gate_area_no_mm(unsigned long addr)
+{
+        return in_gate_area(NULL, addr);
 }
 
 const char *arch_vma_name(struct vm_area_struct *vma)
 {
-        return (vma->vm_start == 0xffff0000) ? "[vectors]" : NULL;
+        return (vma == &gate_vma) ? "[vectors]" : NULL;
 }
 #endif