On Wed, Aug 09, 2017 at 12:43:33PM +0200, Laurent Dufour wrote:

On 09/08/2017 12:12, Kirill A. Shutemov wrote:

quoted

On Tue, Aug 08, 2017 at 04:35:38PM +0200, Laurent Dufour wrote:

quoted

The VMA sequence count has been introduced to allow fast detection of
VMA modification when running a page fault handler without holding
the mmap_sem.

This patch provides protection agains the VMA modification done in :
	- madvise()
	- mremap()
	- mpol_rebind_policy()
	- vma_replace_policy()
	- change_prot_numa()
	- mlock(), munlock()
	- mprotect()
	- mmap_region()
	- collapse_huge_page()

I don't thinks it's anywhere near complete list of places where we touch
vm_flags. What is your plan for the rest?

The goal is only to protect places where change to the VMA is impacting the
page fault handling. If you think I missed one, please advise.

That's very fragile approach. We rely here too much on specific compiler behaviour.

Any write access to vm_flags can, in theory, be translated to several
write accesses. For instance with setting vm_flags to 0 in the middle,
which would result in sigfault on page fault to the vma.

Nothing (apart from common sense) prevents compiler from generating this
kind of pattern.

-- 
 Kirill A. Shutemov