On 08/22/2018 02:10 PM, Kirill A. Shutemov wrote: >> For x86, mpx_notify_unmap() looks finally zap the VM_MPX vmas in bound table >> range with zap_page_range() and doesn't update vm flags, so it sounds ok to >> me since vmas have been detached, nobody can find those vmas. But, I'm not >> familiar with the details of mpx, maybe Kirill could help to confirm this? > I don't see anything obviously dependent on down_write() in > mpx_notify_unmap(), but Dave should know better. We need mmap_sem for write in mpx_notify_unmap(). Its job is to clean up bounds tables, but bounds tables are dynamically allocated and destroyed by the kernel. When we destroy a table, we also destroy the VMA for the bounds table *itself*, separate from the VMA being unmapped. But, this code is very likely to go away soon. If it's causing a problem for you, let me know and I'll see if I can get to removing it faster.
