From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 0/5] Split the emulator: decode & execute Date: Mon, 17 Sep 2007 21:16:50 +0200 Message-ID: <46EED2A2.8090803@qumranet.com> References: <46D5A151.80000@bull.net> <46E3E3D4.1050206@qumranet.com> <46EAB36E.2060004@bull.net> <46EABD97.5060503@qumranet.com> <46EEA801.20404@bull.net> <46EEB971.9000507@qumranet.com> <46EED091.2090404@bull.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel To: "Laurent Vivier (Bull)" Return-path: In-Reply-To: <46EED091.2090404-6ktuUTfB/bM@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org Laurent Vivier (Bull) wrote: > > > > Not being able to emulate is sometimes legitimate. In the case of > > writing to a write-protected guest page table, we simply > > un-write-protect it and go back to the guest (which should now execute > > the instruction natively). > > > > Perhaps the logic that deals with this (the call to > > kvm_mmu_unprotect_page_virt() in emulate_instruction()) was broken by > > your changes. > > > > In fact this case is managed in the error cases of > emulate_instruction(). My first patch removes this management for > instruction decoding because I supposed it cannot generate such errors. > So what I proposed in my last email seems to be the good solution : > > emulate_instruction() > ... > r = x86_decode_insn(&vcpu->emulate_ctxt, &emulate_ops); > if (r == 0) > r = x86_emulate_insn(&vcpu->emulate_ctxt, &emulate_ops); > ... > if (r) { > if (kvm_mmu_unprotect_page_virt(vcpu, cr2)) > return EMULATE_DONE; > if (!vcpu->mmio_needed) { > kvm_report_emulation_failure(vcpu, "mmio"); > return EMULATE_FAIL; > } > return EMULATE_DO_MMIO; > } > ... > Yes. But pushing the kvm_mmu_unprotect_page() to immediately after the decode stage may be better. -- Any sufficiently difficult bug is indistinguishable from a feature. ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2005. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/