Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754400Ab0F2It0 (ORCPT ); Tue, 29 Jun 2010 04:49:26 -0400 Received: from mx1.redhat.com ([209.132.183.28]:23916 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754114Ab0F2ItZ (ORCPT ); Tue, 29 Jun 2010 04:49:25 -0400 Message-ID: <4C29B390.80602@redhat.com> Date: Tue, 29 Jun 2010 11:49:20 +0300 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100430 Fedora/3.0.4-3.fc13 Thunderbird/3.0.4 MIME-Version: 1.0 To: Xiao Guangrong CC: Marcelo Tosatti , LKML , KVM list Subject: Re: [PATCH v2 3/10] KVM: MMU: fix direct sp's access corruptted References: <4C2498EC.2010006@cn.fujitsu.com> <4C249BAD.6000609@cn.fujitsu.com> <4C287081.40300@redhat.com> <4C287332.5080803@cn.fujitsu.com> <4C2883D3.2050606@redhat.com> <4C2949A5.1070303@cn.fujitsu.com> <4C299B7E.5020303@redhat.com> <4C29A25C.7040900@cn.fujitsu.com> In-Reply-To: <4C29A25C.7040900@cn.fujitsu.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2958 Lines: 88 On 06/29/2010 10:35 AM, Xiao Guangrong wrote: > >> We have now >> >> if (is_shadow_present_pte(*sptep)&& !is_large_pte(*sptep)) >> continue; >> >> So we need to add a check, if sp->role.access doesn't match pt_access& >> pte_access, we need to get a new sp with the correct access (can only >> change read->write). >> >> > Umm, we should update the spte at the gw->level, so we need get the child > sp, and compare its access at this point, just like this: > > if (level == gw->level&& is_shadow_present_pte(*sptep)) { > child_sp = page_header(__pa(*sptep& PT64_BASE_ADDR_MASK)); > > if (child_sp->access != pt_access& pte_access& (diry ? 1 : ~ACC_WRITE_MASK )) { > /* Zap sptep */ > ...... > } > > } > > So, why not use the new spte flag (SPTE_NO_DIRTY in my patch) to mark this spte then we can see > this spte whether need updated directly? i think it more simpler ;-) > It's new state, and new state means more maintenance of that state and the need to consider the state in all relevant code paths. In terms of maintainability, changing walk_addr() is best, since it maintains the tight invariant that PT_PAGE_DIRECTORY_LEVEL sptes are always consistent with their sptes. Updating fetch() to allow for a relaxed invariant (spte may be read-only while gpte is write-dirty) is more complicated, but performs better. This is also consistent with what we do with PT_PAGE_TABLE_LEVEL gptes/sptes and with unsync pages. btw, how can the patch work? > > + if (level == gw->level&& !dirty&& > + access& gw->pte_access& ACC_WRITE_MASK) > + spte |= SPTE_NO_DIRTY; > + > spte = __pa(sp->spt) > | PT_PRESENT_MASK | PT_ACCESSED_MASK > | PT_WRITABLE_MASK | PT_USER_MASK; > spte is immediately overwritten by the following assignment. However, the other half of the patch can be adapted: > > + if (*sptep& SPTE_NO_DIRTY) { > + struct kvm_mmu_page *child; > + > + WARN_ON(level != gw->level); > + WARN_ON(!is_shadow_present_pte(*sptep)); > + if (dirty) { > + child = page_header(*sptep& > + PT64_BASE_ADDR_MASK); > + mmu_page_remove_parent_pte(child, sptep); > + __set_spte(sptep, shadow_trap_nonpresent_pte); > + kvm_flush_remote_tlbs(vcpu->kvm); > + } > + } > + > if (is_shadow_present_pte(*sptep)&& !is_large_pte(*sptep)) > continue; > Simply replace (*spte & SPTE_NO_DIRTY) with a condition that checks whether sp->access is consistent with gw->pt(e)_access. Can you write a test case for qemu-kvm.git/kvm/test that demonstrates the problem and the fix? It will help ensure we don't regress in this area. -- error compiling committee.c: too many arguments to function -- 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/