1 files changed, 74 insertions, 0 deletions

diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index e5dad60b558b..cf4528d51774 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -791,6 +791,79 @@ void __init iotable_init(struct map_desc *io_desc, int nr)
         }
 }
 
+#ifndef CONFIG_ARM_LPAE
+
+/*
+ * The Linux PMD is made of two consecutive section entries covering 2MB
+ * (see definition in include/asm/pgtable-2level.h).  However a call to
+ * create_mapping() may optimize static mappings by using individual
+ * 1MB section mappings.  This leaves the actual PMD potentially half
+ * initialized if the top or bottom section entry isn't used, leaving it
+ * open to problems if a subsequent ioremap() or vmalloc() tries to use
+ * the virtual space left free by that unused section entry.
+ *
+ * Let's avoid the issue by inserting dummy vm entries covering the unused
+ * PMD halves once the static mappings are in place.
+ */
+
+static void __init pmd_empty_section_gap(unsigned long addr)
+{
+        struct vm_struct *vm;
+
+        vm = early_alloc_aligned(sizeof(*vm), __alignof__(*vm));
+        vm->addr = (void *)addr;
+        vm->size = SECTION_SIZE;
+        vm->flags = VM_IOREMAP | VM_ARM_STATIC_MAPPING;
+        vm->caller = pmd_empty_section_gap;
+        vm_area_add_early(vm);
+}
+
+static void __init fill_pmd_gaps(void)
+{
+        struct vm_struct *vm;
+        unsigned long addr, next = 0;
+        pmd_t *pmd;
+
+        /* we're still single threaded hence no lock needed here */
+        for (vm = vmlist; vm; vm = vm->next) {
+                if (!(vm->flags & VM_ARM_STATIC_MAPPING))
+                        continue;
+                addr = (unsigned long)vm->addr;
+                if (addr < next)
+                        continue;
+
+                /*
+                 * Check if this vm starts on an odd section boundary.
+                 * If so and the first section entry for this PMD is free
+                 * then we block the corresponding virtual address.
+                 */
+                if ((addr & ~PMD_MASK) == SECTION_SIZE) {
+                        pmd = pmd_off_k(addr);
+                        if (pmd_none(*pmd))
+                                pmd_empty_section_gap(addr & PMD_MASK);
+                }
+
+                /*
+                 * Then check if this vm ends on an odd section boundary.
+                 * If so and the second section entry for this PMD is empty
+                 * then we block the corresponding virtual address.
+                 */
+                addr += vm->size;
+                if ((addr & ~PMD_MASK) == SECTION_SIZE) {
+                        pmd = pmd_off_k(addr) + 1;
+                        if (pmd_none(*pmd))
+                                pmd_empty_section_gap(addr);
+                }
+
+                /* no need to look at any vm entry until we hit the next PMD */
+                next = (addr + PMD_SIZE - 1) & PMD_MASK;
+        }
+}
+
+#else
+#define fill_pmd_gaps() do { } while (0)
+#endif
+
 static void * __initdata vmalloc_min =
         (void *)(VMALLOC_END - (240 << 20) - VMALLOC_OFFSET);
 
@@ -1072,6 +1145,7 @@ static void __init devicemaps_init(struct machine_desc *mdesc)
          */
         if (mdesc->map_io)
                 mdesc->map_io();
+        fill_pmd_gaps();
 
         /*
          * Finally flush the caches and tlb to ensure that we're in a