[PATCH] arch, mm: introduce arch_tlb_gather_mmu_lazy (was: Re: [RESEND PATCH] mm, oom_reaper: gather each vma to prevent) leaking TLB entry

[Michal Hocko <mhocko@kernel.org>]

On Fri 10-11-17 11:15:29, Michal Hocko wrote:
> On Fri 10-11-17 09:19:33, Minchan Kim wrote:
> > On Tue, Nov 07, 2017 at 09:54:53AM +0000, Wang Nan wrote:
> > > tlb_gather_mmu(&tlb, mm, 0, -1) means gathering the whole virtual memory
> > > space. In this case, tlb->fullmm is true. Some archs like arm64 doesn't
> > > flush TLB when tlb->fullmm is true:
> > > 
> > >   commit 5a7862e83000 ("arm64: tlbflush: avoid flushing when fullmm == 1").
> > > 
> > > Which makes leaking of tlb entries.
> > 
> > That means soft-dirty which has used tlb_gather_mmu with fullmm could be
> > broken via losing write-protection bit once it supports arm64 in future?
> > 
> > If so, it would be better to use TASK_SIZE rather than -1 in tlb_gather_mmu.
> > Of course, it's a off-topic.
> 
> I wouldn't play tricks like that. And maybe the API itself could be more
> explicit. E.g. add a lazy parameter which would allow arch specific code
> to not flush if it is sure that nobody can actually stumble over missed
> flush. E.g. the following?

This one has a changelog and even compiles on my crosscompile test
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