From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xiao Guangrong Subject: Re: [PATCH 6/9] KVM: MMU: introduce the framework to check reserved bits on sptes Date: Tue, 4 Aug 2015 21:34:38 +0800 Message-ID: <55C0BF6E.2060304@linux.intel.com> References: <1438685961-8107-1-git-send-email-guangrong.xiao@linux.intel.com> <1438685961-8107-7-git-send-email-guangrong.xiao@linux.intel.com> <55C0AC9C.6070606@redhat.com> <55C0B9B1.9070504@linux.intel.com> <55C0BCB4.3020601@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Cc: gleb@kernel.org, mtosatti@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org To: Paolo Bonzini Return-path: In-Reply-To: <55C0BCB4.3020601@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 08/04/2015 09:23 PM, Paolo Bonzini wrote: > > > On 04/08/2015 15:10, Xiao Guangrong wrote: >>> >>> This should be cpu_has_nx, I think. >> >> cpu_has_nx() checks the feature on host CPU, however, this is the shadow >> page table which completely follow guest's features. >> >> E.g, if guest does not execution-protect the physical page, then >> KVM does not do it either. > > That's just true for current code. In principle you could add a memslot > flag for KVM_MEMSLOT_NO_EXECUTE, then NX would be true on an spte but > not on a PTE. Yes, i agree. I would like to keep it as strict as possible to catch potential bugs. We can relax it while KVM_MEMSLOT_NO_EXECUTE is being developed. > >>> >>>> + guest_cpuid_has_gbpages(vcpu), >>> >>> This should be cpu_has_gbpages. >> >> E.g, if guest does not use 1G page size, it's also not used in shadow page >> table. > > However, bit 7 in the shadow PDPTE is not reserved. If you're not > testing "is this bit reserved" but rather "should this bit be always > zero" in the SPTE, then checking guest_cpuid is okay. But in that case > shadow_rsvd_check is really more like shadow_always_zero_check. Yes, it is not reserved in hardware's point of view. shadow_always_zero_check() seems a more meaningful name, thanks for your suggestion. :) > >>> >>>> is_pse(vcpu)); >>> >>> This should be cpu_has_pse. >> >> E.g, guest does no use 4M page size, then KVM does not use it either. > > Right, it should always be true, not cpu_has_pse, because PAE and 64-bit > page tables always support huge (2M) pages. Or as above, if you're > testing "should this bit be always zero" then it's a different story. Yeah, i will rename the function.