Re: usbdev_mmap causes type confusion in page_table_check

[Pasha Tatashin]

> For normal Kernel-MM operations, vm_normal_page() should be used to
> get "struct page" based on vma+addr+pte combination, but
> page_table_check does not use vma for its operation in order to
> strengthen the verification of no invalid page sharing. But, even
> vm_normal_page() can cause access to the "struct page" for VM_PFNMAP
> if pfn_valid(pfn) is true. So, vm_normal_page() can return a struct
> page for a user mapped slab page.

Only for !ARCH_HAS_PTE_SPECIAL case, otherwise NULL is returned.

Pasha