Re: [PATCH 2/6] mm/mremap: For MREMAP_DONTUNMAP check security_vm_enough_memory_mm()

[Dmitry Safonov]

On 12/28/20 6:21 PM, Brian Geffon wrote:
> This looks good to me with a small comment.
> 
>>         if (do_munmap(mm, old_addr, old_len, uf_unmap) < 0) {
>>                 /* OOM: unable to split vma, just get accounts right */
>> -               if (vm_flags & VM_ACCOUNT)
>> +               if (vm_flags & VM_ACCOUNT && !(flags & MREMAP_DONTUNMAP))
>>                         vm_acct_memory(new_len >> PAGE_SHIFT);
> 
> Checking MREMAP_DONTUNMAP in the do_munmap path is unnecessary as
> MREMAP_DONTUNMAP will have already returned by this point.

In this code it is also used as err-path. In case move_page_tables()
fails to move all page tables or .mremap() callback fails, the new VMA
is unmapped.

IOW, MREMAP_DONTUNMAP returns under:
:	if (unlikely(!err && (flags & MREMAP_DONTUNMAP))) {

-- 
          Dima