From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [patch 3/4] KVM: MMU: reload request from GET_DIRTY_LOG path Date: Mon, 6 Oct 2014 14:19:32 -0300 Message-ID: <20141006171932.GA1011@amt.cnet> References: <20140709191250.408928362@amt.cnet> <20140709191611.280800634@amt.cnet> <20140721131424.GZ18167@minantech.com> <20140909152811.GA4153@amt.cnet> <20141004072332.GS26540@minantech.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kvm@vger.kernel.org, ak@linux.intel.com, pbonzini@redhat.com, xiaoguangrong@linux.vnet.ibm.com, avi.kivity@gmail.com To: Gleb Natapov Return-path: Received: from mx1.redhat.com ([209.132.183.28]:36353 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752318AbaJFRT5 (ORCPT ); Mon, 6 Oct 2014 13:19:57 -0400 Content-Disposition: inline In-Reply-To: <20141004072332.GS26540@minantech.com> Sender: kvm-owner@vger.kernel.org List-ID: On Sat, Oct 04, 2014 at 10:23:32AM +0300, Gleb Natapov wrote: > On Tue, Sep 09, 2014 at 12:28:11PM -0300, Marcelo Tosatti wrote: > > On Mon, Jul 21, 2014 at 04:14:24PM +0300, Gleb Natapov wrote: > > > On Wed, Jul 09, 2014 at 04:12:53PM -0300, mtosatti@redhat.com wrote: > > > > Reload remote vcpus MMU from GET_DIRTY_LOG codepath, before > > > > deleting a pinned spte. > > > > > > > > Signed-off-by: Marcelo Tosatti > > > > > > > > --- > > > > arch/x86/kvm/mmu.c | 29 +++++++++++++++++++++++------ > > > > 1 file changed, 23 insertions(+), 6 deletions(-) > > > > > > > > Index: kvm.pinned-sptes/arch/x86/kvm/mmu.c > > > > =================================================================== > > > > --- kvm.pinned-sptes.orig/arch/x86/kvm/mmu.c 2014-07-09 11:23:59.290744490 -0300 > > > > +++ kvm.pinned-sptes/arch/x86/kvm/mmu.c 2014-07-09 11:24:58.449632435 -0300 > > > > @@ -1208,7 +1208,8 @@ > > > > * > > > > * Return true if tlb need be flushed. > > > > */ > > > > -static bool spte_write_protect(struct kvm *kvm, u64 *sptep, bool pt_protect) > > > > +static bool spte_write_protect(struct kvm *kvm, u64 *sptep, bool pt_protect, > > > > + bool skip_pinned) > > > > { > > > > u64 spte = *sptep; > > > > > > > > @@ -1218,6 +1219,22 @@ > > > > > > > > rmap_printk("rmap_write_protect: spte %p %llx\n", sptep, *sptep); > > > > > > > > + if (is_pinned_spte(spte)) { > > > > + /* keep pinned spte intact, mark page dirty again */ > > > > + if (skip_pinned) { > > > > + struct kvm_mmu_page *sp; > > > > + gfn_t gfn; > > > > + > > > > + sp = page_header(__pa(sptep)); > > > > + gfn = kvm_mmu_page_get_gfn(sp, sptep - sp->spt); > > > > + > > > > + mark_page_dirty(kvm, gfn); > > > > + return false; > > > Why not mark all pinned gfns as dirty in kvm_vm_ioctl_get_dirty_log() while > > > populating dirty_bitmap_buffer? > > > > The pinned gfns are per-vcpu. Requires looping all vcpus (not > > scalable). > > > OK, but do they really have to be per-cpu? What's the advantage? The guest configures pinning on a per-cpu basis (that is, enabling PEBS is done on a per-cpu basis). > > > > > > + } else > > > > + mmu_reload_pinned_vcpus(kvm); > > > Can you explain why do you need this? > > > > Because if skip_pinned = false, we want vcpus to exit (called > > from enable dirty logging codepath). > > > I guess what I wanted to ask is why do we need skip_pinned? As far as I see it > is set to false in two cases: > 1: page is write protected for shadow MMU needs, should not happen since the feature Correct. > is not supported with shadow mmu (can happen with nested EPT, but page will be marked > is accessed during next vcpu entry anyway, so how will it work)? PEBS is not supported on nested EPT. > 2: when slot is marked as read only: such slot cannot have PEBS pages and if it will guest will die > anyway during next guest entry, so why not maintain list of pinned pages per slot and kill aguest > if slot with pinned pages is marked read only. 2: when slots pages have dirty logging enabled. In that case, the page is marked dirty immediately. This is the call from kvm_mmu_slot_remove_write_access. So when enabling dirty logging, for pinned sptes: - maintain pinned spte intact. - mark gfn for which pinned spte represents as dirty in the dirty log.