On 2016/4/23 2:38, Andrew Morton wrote:
On Fri, 22 Apr 2016 18:31:28 +0800 Yongji Xie <[email protected]> wrote:We used generic hooks in remap_pfn_range to help archs to track pfnmap regions. The code is something like: int remap_pfn_range() { ... track_pfn_remap(vma, &prot, pfn, addr, PAGE_ALIGN(size)); ... pfn -= addr >> PAGE_SHIFT; ... untrack_pfn(vma, pfn, PAGE_ALIGN(size)); ... } Here we can easily find the pfn is changed but not recovered before untrack_pfn() is called. That's incorrect.What are the runtime effects of this bug?
No， this is just a fix in theory:-) .
--- a/mm/memory.c +++ b/mm/memory.c @@ -1755,6 +1755,7 @@ int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr, break; } while (pgd++, addr = next, addr != end);+ pfn += (end - PAGE_ALIGN(size)) >> PAGE_SHIFT;if (err) untrack_pfn(vma, pfn, PAGE_ALIGN(size));I'm having trouble understanding this. Wouldn't it be better to simply save the track_pfn_remap() call's `pfn' arg in a new local variable?
Yes, it's a little difficult to understand this. I will send a v2 soon. Thanks, Yongji
