From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: KVM: MMU: only write protect mappings at pagetable level Date: Wed, 22 Dec 2010 13:07:23 +0200 Message-ID: <4D11DBEB.8050008@redhat.com> References: <20101222110157.GA4266@amt.cnet> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm To: Marcelo Tosatti Return-path: Received: from mx1.redhat.com ([209.132.183.28]:27560 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751501Ab0LVLH0 (ORCPT ); Wed, 22 Dec 2010 06:07:26 -0500 Received: from int-mx12.intmail.prod.int.phx2.redhat.com (int-mx12.intmail.prod.int.phx2.redhat.com [10.5.11.25]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id oBMB7Qeo025874 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Wed, 22 Dec 2010 06:07:26 -0500 In-Reply-To: <20101222110157.GA4266@amt.cnet> Sender: kvm-owner@vger.kernel.org List-ID: On 12/22/2010 01:01 PM, Marcelo Tosatti wrote: > If a pagetable contains a writeable large spte, all of its sptes will be non-writeable > write protected, including non-leaf ones, leading to endless pagefaults. > > Do not write protect pages above PT_PAGE_TABLE_LEVEL, as the spte fault > paths assume non-leaf sptes are writable. > > Signed-off-by: Marcelo Tosatti > > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > index c3853d5..c716ff8 100644 > --- a/arch/x86/kvm/mmu.c > +++ b/arch/x86/kvm/mmu.c > @@ -3442,6 +3442,9 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot) > if (!test_bit(slot, sp->slot_bitmap)) > continue; > > + if (sp->role.level != PT_PAGE_TABLE_LEVEL) > + continue; > + > pt = sp->spt; > for (i = 0; i< PT64_ENT_PER_PAGE; ++i) > /* avoid RMW */ But what about large leaf sptes? Don't we want to write protect, or perhaps drop them? I think write-protecting leaf sptes and ignoring nonleaf sptes should work. -- error compiling committee.c: too many arguments to function