Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933970Ab0GORxj (ORCPT ); Thu, 15 Jul 2010 13:53:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:35812 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933930Ab0GORxi (ORCPT ); Thu, 15 Jul 2010 13:53:38 -0400 Date: Thu, 15 Jul 2010 13:40:48 -0300 From: Marcelo Tosatti To: Xiao Guangrong Cc: Avi Kivity , LKML , KVM list Subject: Re: [PATCH 3/4] KVM: MMU: track dirty page in speculative path properly Message-ID: <20100715164048.GA6980@amt.cnet> References: <4C3C3518.7080505@cn.fujitsu.com> <4C3C35B7.50101@cn.fujitsu.com> <20100713220551.GB6370@amt.cnet> <4C3D11C6.4000101@cn.fujitsu.com> <20100714110926.GA26033@amt.cnet> <4C3DB942.3010709@cn.fujitsu.com> <20100714140626.GA28485@amt.cnet> <4C3EBC70.2030604@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4C3EBC70.2030604@cn.fujitsu.com> User-Agent: Mutt/1.5.20 (2009-08-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2396 Lines: 62 On Thu, Jul 15, 2010 at 03:44:48PM +0800, Xiao Guangrong wrote: > > > Marcelo Tosatti wrote: > > >> How about just track access bit for speculative path, we set page both accessed and > >> dirty(if it's writable) only if the access bit is set? > > > > A useful thing to do would be to allow read-only mappings, in the fault > > path (Lai sent a few patches in that direction sometime ago but there > > was no follow up). > > > > So in the case of a read-only fault from the guest, you'd inform > > get_user_pages() that read-only access is acceptable (so swapcache pages > > can be mapped, or qemu can mprotect(PROT_READ) guest memory). > > > > Yeah, it's a great work, i guess Lai will post the new version soon. > > And, even we do this, i think the page dirty track is still needed, right? > Then, how about my new idea to track page dirty for speculative path, just > as below draft patch does: > > @@ -687,10 +687,11 @@ static void drop_spte(struct kvm *kvm, u64 *sptep, u64 new_spte) > if (!is_rmap_spte(old_spte)) > return; > pfn = spte_to_pfn(old_spte); > - if (old_spte & shadow_accessed_mask) > + if (old_spte & shadow_accessed_mask) { > kvm_set_pfn_accessed(pfn); > - if (is_writable_pte(old_spte)) > - kvm_set_pfn_dirty(pfn); > + if (is_writable_pte(old_spte)) > + kvm_set_pfn_dirty(pfn); > + } > rmap_remove(kvm, sptep); > } > > @@ -1920,8 +1921,11 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep, > * demand paging). > */ > spte = shadow_base_present_pte | shadow_dirty_mask; > - if (!speculative) > + if (!speculative) { > spte |= shadow_accessed_mask; > + if (is_writable_pte(*sptep)) > + kvm_set_pfn_dirty(pfn); > + } > if (!dirty) > pte_access &= ~ACC_WRITE_MASK; > if (pte_access & ACC_EXEC_MASK) > > It uses access bit to track both page accessed and page dirty, and it's rather cheap... Xiao, I don't understand it. What are you trying to achieve? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/