On Wed, Oct 22, 2014 at 02:26:57PM +0300, Kirill A. Shutemov wrote: > On Mon, Oct 20, 2014 at 11:56:36PM +0200, Peter Zijlstra wrote: > > Wrap the VMA modifications (vma_adjust/unmap_page_range) with sequence > > counts such that we can easily test if a VMA is changed. > > > > The unmap_page_range() one allows us to make assumptions about > > page-tables; when we find the seqcount hasn't changed we can assume > > page-tables are still valid. > > > > The flip side is that we cannot distinguish between a vma_adjust() and > > the unmap_page_range() -- where with the former we could have > > re-checked the vma bounds against the address. > > You only took care about changing size of VMA or unmap. What about other > aspects of VMA. How would you care about race with mprotect(2)? > > CPU0 CPU1 > mprotect() > mprotect_fixup() > vma_merge() > [ maybe update vm_sequence ] > [ page fault kicks in ] > do_anonymous_page() > entry = mk_pte(page, fe->vma->vm_page_prot); > vma_set_page_prot(vma) > [ update vma->vm_page_prot ] > change_protection() > pte_map_lock() > [ vm_sequence is ok ] > set_pte_at(entry) // With old vm_page_prot!!! > This won't happen, this is be serialized by the PTL and the fault validates that the PTE is the 'same' it started out with after acquiring the PTL. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>