Avi Kivity wrote: > On 04/25/2010 10:00 AM, Xiao Guangrong wrote: >> Two cases maybe happen in kvm_mmu_get_page() function: >> >> - one case is, the goal sp is already in cache, if the sp is unsync, >> we only need update it to assure this mapping is valid, but not >> mark it sync and not write-protect sp->gfn since it not broke unsync >> rule(one shadow page for a gfn) >> >> - another case is, the goal sp not existed, we need create a new sp >> for gfn, i.e, gfn (may)has another shadow page, to keep unsync rule, >> we should sync(mark sync and write-protect) gfn's unsync shadow page. >> After enabling multiple unsync shadows, we sync those shadow pages >> only when the new sp not allow to become unsync(also for the unsyc >> rule, the new rule is: allow all pte page become unsync) >> > > Another interesting case is to create new shadow pages in the unsync > state. That can help when the guest starts a short lived process: we > can avoid write protecting its pagetables completely. Even if we do > sync them, we can sync them in a batch instead of one by one, saving IPIs.
IPI is needed when rmap_write_protect() changes mappings form writable to read-only, so while we sync all gfn's unsync page, only one IPI is needed. And, another problem is we call ramp_write_protect()/flush-local-tlb many times when sync gfn's unsync page, the same problem is in mmu_sync_children() function, could you allow me to improve it after this patchset? :-) -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
