mm: fix ambiguous comments for better code readability

The parameter of remap_pfn_range() @pfn passed from the caller is actually
a page-frame number converted by corresponding physical address of kernel
memory, the original comment is ambiguous that may mislead the users.

Meanwhile, there is an ambiguous typo "VMM" in the comment of
vm_area_struct.  So fixing them will make the code more readable.
Signed-off-by: chenqiwu <chenqiwu@xiaomi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/1583026921-15279-1-git-send-email-qiwuchen55@gmail.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mm_types.h

@@ -289,7 +289,7 @@ struct vm_userfaultfd_ctx {};
 #endif /* CONFIG_USERFAULTFD */
 
 /*
- * This struct defines a memory VMM memory area. There is one of these
+ * This struct describes a virtual memory area. There is one of these
  * per VM-area/task. A VM area is any part of the process virtual memory
  * space that has a special rule for the page-fault handlers (ie a shared
  * library, the executable area etc).

mm/memory.c

@@ -1952,7 +1952,7 @@ static inline int remap_p4d_range(struct mm_struct *mm, pgd_t *pgd,
  * @vma: user vma to map to
  * @addr: target user address to start at
  * @pfn: page frame number of kernel physical memory address
- * @size: size of map area
+ * @size: size of mapping area
  * @prot: page protection flags for this mapping
  *
  * Note: this is only safe if the mm semaphore is held when called.