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 e6sPnax7 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/2/24 10:35 AM, Dave Hansen wrote: > We were just chatting about this on David Rientjes's MM alignment call. > I thought I'd try to give a little brain > > Let's start by thinking about KVM and secondary MMUs. KVM has a primary > mm: the QEMU (or whatever) process mm. The virtualization (EPT/NPT) > tables get entries that effectively mirror the primary mm page tables > and constitute a secondary MMU. If the primary page tables change, > mmu_notifiers ensure that the changes get reflected into the > virtualization tables and also that the virtualization paging structure > caches are flushed. > > msharefs is doing something very similar. But, in the msharefs case, > the secondary MMUs are actually normal CPU MMUs. The page tables are > normal old page tables and the caches are the normal old TLB. That's > what makes it so confusing: we have lots of infrastructure for dealing > with that "stuff" (CPU page tables and TLB), but msharefs has > short-circuited the infrastructure and it doesn't work any more. > > Basically, I think it makes a lot of sense to check what KVM (or another > mmu_notifier user) is doing and make sure that msharefs is following its > lead. For instance, KVM _should_ have the exact same "page free" > flushing issue where it gets the MMU notifier call but the page may > still be in the secondary MMU. I _think_ KVM fixes it with an extra > page refcount that it takes when it first walks the primary page tables. > > But the short of it is that the msharefs host mm represents a "secondary > MMU". I don't think it is really that special of an MMU other than the > fact that it has an mm_struct. Thanks, Dave. This is helpful. I'll look at what other mmu notifier users are doing. This does align with the comments in mmu_notifier.h regarding invalidate_range_start/end. Anthony