From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 0/4] Unlocked TLB flush Date: Tue, 08 May 2012 13:51:26 +0300 Message-ID: <4FA8FAAE.5030300@redhat.com> References: <1336044182-12023-1-git-send-email-avi@redhat.com> <20120508012534.GA26243@amt.cnet> <20120508012741.GA26336@amt.cnet> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, Xiao Guangrong , takuya.yoshikawa@gmail.com To: Marcelo Tosatti Return-path: Received: from mx1.redhat.com ([209.132.183.28]:56861 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752612Ab2EHKvb (ORCPT ); Tue, 8 May 2012 06:51:31 -0400 In-Reply-To: <20120508012741.GA26336@amt.cnet> Sender: kvm-owner@vger.kernel.org List-ID: On 05/08/2012 04:27 AM, Marcelo Tosatti wrote: > On Mon, May 07, 2012 at 10:25:34PM -0300, Marcelo Tosatti wrote: > > On Thu, May 03, 2012 at 02:22:58PM +0300, Avi Kivity wrote: > > > This patchset implements unlocked TLB flushing for KVM. An operation that > > > generates stale TLB entries can mark the TLB as dirty instead of flushing > > > immediately, and then flush after releasing mmu_lock but before returning > > > to the guest or the caller. A few call sites are converted too. > > > > > > Note not all call sites are easily convertible; as an example, sync_page() > > > must flush before reading the guest page table. > > > > Huh? Are you referring to: > > > > * Note: > > * We should flush all tlbs if spte is dropped even though guest is > > * responsible for it. Since if we don't, > > * kvm_mmu_notifier_invalidate_page > > * and kvm_mmu_notifier_invalidate_range_start detect the mapping page > > * isn't > > * used by guest then tlbs are not flushed, so guest is allowed to > > * access the > > * freed pages. > > * And we increase kvm->tlbs_dirty to delay tlbs flush in this case. > > > > With an increased dirtied_count the flush can be performed > > by kvm_mmu_notifier_invalidate_page. > > Which is what patch 1 does. Your comment regarding sync_page() > above is what is outdated, unless i am missing something. I wasn't referring to that. sync_page() (and page_fault()) must be sure the guest page table is write-protected before reading gptes from it. (page_fault() reads it before write protection, but verifies it afterwards: /* * Verify that the gpte in the page we've just write * protected is still there. */ if (FNAME(gpte_changed)(vcpu, gw, it.level - 1)) goto out_gpte_changed; so we must kvm_cond_flush_remote_tlbs() before calling gpte_changed(). -- error compiling committee.c: too many arguments to function