On Wed, May 22, 2013 at 04:46:04PM +0800, Xiao Guangrong wrote: > On 05/22/2013 02:34 PM, Gleb Natapov wrote: > > 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? > > I do not know too... I even do no know why kvm_flush_remote_tlbs > is needed. :( We changed the content of an executable page, we need to flush instruction cache of all vcpus to not use stale data, so my suggestion to call kvm_flush_remote_tlbs() is obviously incorrect since this flushes tlb, not instruction cache, but why kvm_reload_remote_mmus() would flush instruction cache? -- 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
