From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 4/7] kvm mmu: implement necessary data structures for second huge page accounting Date: Sun, 29 Mar 2009 16:37:38 +0300 Message-ID: <49CF79A2.9020202@redhat.com> References: <1238164319-16092-1-git-send-email-joerg.roedel@amd.com> <1238164319-16092-5-git-send-email-joerg.roedel@amd.com> <49CF7716.1000008@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti , kvm@vger.kernel.org, linux-kernel@vger.kernel.org To: Joerg Roedel Return-path: Received: from mx2.redhat.com ([66.187.237.31]:42803 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751293AbZC2Nho (ORCPT ); Sun, 29 Mar 2009 09:37:44 -0400 In-Reply-To: <49CF7716.1000008@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: Avi Kivity wrote: > Joerg Roedel wrote: >> This patch adds the necessary data structures to take care of write >> protections in place within a second huge page sized page. >> >> >> +#ifdef KVM_PAGES_PER_LHPAGE >> + if (npages && !new.hpage_info) { >> + int hugepages = npages / KVM_PAGES_PER_LHPAGE; >> + if (npages % KVM_PAGES_PER_LHPAGE) >> + hugepages++; >> + if (base_gfn % KVM_PAGES_PER_LHPAGE) >> + hugepages++; >> > > Consider a slot with base_gfn == 1 and npages == 1. This will have > hugepages == 2, which is wrong. > > I think the right calculation is > > ((base_gfn + npages - 1) / N) - (base_gfn / N) + 1 > > i.e. index of last page, plus one so we can store it. > > The small huge page calculation is off as well. > I fixed the existing case with commit 1a967084dbe97a2f4be84139d14e2d958d7ffc46 Author: Avi Kivity Date: Sun Mar 29 16:31:25 2009 +0300 KVM: MMU: Fix off-by-one calculating large page count The large page initialization code concludes there are two large pages spanned by a slot covering 1 (small) page starting at gfn 1. This is incorrect, and also results in incorrect write_count initialization in some cases (base = 1, npages = 513 for example). Cc: stable@kernel.org Signed-off-by: Avi Kivity diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 8aa3b95..3d31557 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1076,6 +1076,7 @@ int __kvm_set_memory_region(struct kvm *kvm, int r; gfn_t base_gfn; unsigned long npages; + int largepages; unsigned long i; struct kvm_memory_slot *memslot; struct kvm_memory_slot old, new; @@ -1151,11 +1152,8 @@ int __kvm_set_memory_region(struct kvm *kvm, new.userspace_addr = 0; } if (npages && !new.lpage_info) { - int largepages = npages / KVM_PAGES_PER_HPAGE; - if (npages % KVM_PAGES_PER_HPAGE) - largepages++; - if (base_gfn % KVM_PAGES_PER_HPAGE) - largepages++; + largepages = 1 + (base_gfn + npages - 1) / KVM_PAGES_PER_HPAGE; + largepages -= base_gfn / npages; new.lpage_info = vmalloc(largepages * sizeof(*new.lpage_info)); -- error compiling committee.c: too many arguments to function