From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 2/2] KVM: MMU: fix relaxing permission Date: Thu, 27 May 2010 14:54:32 +0300 Message-ID: <4BFE5D78.5040204@redhat.com> References: <4BFC8B0D.2060106@cn.fujitsu.com> <4BFC8B8C.7010402@cn.fujitsu.com> <4BFE4513.8090606@redhat.com> <4BFE50E2.60203@cn.fujitsu.com> <4BFE54F8.7030309@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti , LKML , KVM list To: Xiao Guangrong Return-path: In-Reply-To: <4BFE54F8.7030309@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 05/27/2010 02:18 PM, Avi Kivity wrote: > >> And, i think use 'spte.w=1, spte.u=0' to emulate 'guest cr0.wp=0 and >> gpte.w=0' >> is not a good way since it can completely stop user process access, >> but in this >> case, user process is usually read and kernel lazily to write, just >> like vdso, >> it will generate a lots of #PF > > As soon as the guest kernel stops writing we switch back to > gpte.w=gpte.u=1 and the guest can access it completely. For the case > where both the kernel and userspace use interleaved access, you are > right, but I don't see a better way, do you? To expand, we only set spte.w=1 on write faults. So if the guest only reads the page, we'll instantiate an spte with u=1 and w=0. -- error compiling committee.c: too many arguments to function