Jiri Kosina wrote on Thu, Mar 07, 2019:

quoted

I'm not sure this is correct in all cases.   If

	addr = 4095
	vma->vm_end = 4096
	pages = 1000

then `end' is 4096 and `(end - addr) << PAGE_SHIFT' is zero, but it
should have been 1.

Good catch! It should rather be something like

	unsigned long pages = (end >> PAGE_SHIFT) - (addr >> PAGE_SHIFT);

That would be 0 for addr = 0 and vma->vm_end = 1; I assume we would
still want to count that as one page.
I'm not too familiar with this area of the code, but I think there's a
handy macro we can use for this, perhaps
  DIV_ROUND_UP(end - addr, PAGE_SIZE) ?

kernel/kexec_core.c has defined PAGE_COUNT() which seems more
appropriate but I do not see a global equivalent
#define PAGE_COUNT(x) (((x) + PAGE_SIZE - 1) >> PAGE_SHIFT)

-- 
Dominique