Messages in this thread | | | Date | Tue, 21 May 2013 22:33:30 -0300 | From | Marcelo Tosatti <> | Subject | Re: [PATCH v6 3/7] KVM: MMU: fast invalidate all pages |
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On Tue, May 21, 2013 at 11:39:03AM +0300, Gleb Natapov wrote: > > Any pages with stale information will be zapped by kvm_mmu_zap_all(). > > When that happens, page faults will take place which will automatically > > use the new generation number. > > > > So still not clear why is this necessary. > > > This is not, strictly speaking, necessary, but it is the sane thing to do. > You cannot update page's generation number to prevent it from been > destroyed since after kvm_mmu_zap_all() completes stale ptes in the > shadow page may point to now deleted memslot. So why build shadow page > table with a page that is in a process of been destroyed?
OK, can this be introduced separately, in a later patch, with separate justification, then?
Xiao please have the first patches of the patchset focus on the problem at hand: fix long mmu_lock hold times.
> Not sure what you mean again. We flush TLB once before entering this function. > kvm_reload_remote_mmus() does this for us, no?
kvm_reload_remote_mmus() is used as an optimization, its separate from the problem solution.
> > > > What was suggested was... go to phrase which starts with "The only purpose > > of the generation number should be to". > > > > The comment quoted here does not match that description. > > > The comment describes what code does and in this it is correct. > > You propose to not reload roots right away and do it only when root sp > is encountered, right? So my question is what's the point? There are, > obviously, root sps with invalid generation number at this point, so > reload will happen regardless in kvm_mmu_prepare_zap_page(). So why not > do it here right away and avoid it in kvm_mmu_prepare_zap_page() for > invalid and obsolete sps as I proposed in one of my email?
Sure. But Xiao please introduce that TLB collapsing optimization as a later patch, so we can reason about it in a more organized fashion.
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