On Tue, May 21, 2013 at 10:33:30PM -0300, Marcelo Tosatti wrote: > 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. So, if I understand correctly, you are asking to move is_obsolete_sp() check from kvm_mmu_get_page() and kvm_reload_remote_mmus() from kvm_mmu_invalidate_all_pages() to a separate patch. Fine by me, but if we drop kvm_reload_remote_mmus() from kvm_mmu_invalidate_all_pages() the call to kvm_mmu_invalidate_all_pages() in emulator_fix_hypercall() will become nop. But I question the need to zap all shadow pages tables there in the first place, why kvm_flush_remote_tlbs() is not enough? -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
