From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [PATCHv3] VMX: Enhance invalid guest state emulation Date: Tue, 1 Sep 2009 10:29:38 -0300 Message-ID: <20090901132938.GA19864@amt.cnet> References: <1251802098-23819-1-git-send-email-m.gamal005@gmail.com> <20090901114806.GA18778@amt.cnet> <52d4a3890909010514n20ceef87i4767e277c550a581@mail.gmail.com> <20090901121804.GA19145@amt.cnet> <52d4a3890909010608h1f406b42j98d403493859d6b6@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: avi@redhat.com, kvm@vger.kernel.org To: Mohammed Gamal Return-path: Received: from mx1.redhat.com ([209.132.183.28]:10393 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754596AbZIAN36 (ORCPT ); Tue, 1 Sep 2009 09:29:58 -0400 Content-Disposition: inline In-Reply-To: <52d4a3890909010608h1f406b42j98d403493859d6b6@mail.gmail.com> Sender: kvm-owner@vger.kernel.org List-ID: On Tue, Sep 01, 2009 at 03:08:55PM +0200, Mohammed Gamal wrote: > On Tue, Sep 1, 2009 at 2:18 PM, Marcelo Tosatti wrote: > > On Tue, Sep 01, 2009 at 02:14:17PM +0200, Mohammed Gamal wrote: > >> On Tue, Sep 1, 2009 at 1:48 PM, Marcelo Tosatti wrote: > >> > On Tue, Sep 01, 2009 at 12:48:18PM +0200, Mohammed Gamal wrote: > >> >> - Change returned handle_invalid_guest_state() to return relevant exit codes > >> >> - Move triggering the emulation from vmx_vcpu_run() to vmx_handle_exit() > >> >> - Return to userspace instead of repeatedly trying to emulate instructions that have already failed > >> >> > >> >> Signed-off-by: Mohammed Gamal > >> > > >> > Mohammed, > >> > > >> > The handle_invalid_guest_state loop is potentially problematic. It would > >> > be more appropriate to use the __vcpu_run loop. > >> > > >> > Can't you set vmx->emulation_required depending on the result > >> > of one call to emulate_instruction and get rid of the while > >> > (!guest_state_valid(vcpu)) loop? > >> > > >> > >> Invalid state emulation is VMX-specfic, while the __vcpu_run loop is > >> independent of the virtualization extension (defined in x86.c), no? > >> AMD SVM can comforably run hosts in big-real mode and thus it doesn't > >> have the notion of a guest going to an invalid state because of mode > >> switching, so I don't think it'd be a good idea to move emulation into > >> a generic layer. Please correct me if I am wrong > > > > Right. But all i am asking is to emulate one instruction at a > > time in handle_invalid_guest_state, instead of looping until > > guest_state_valid(vcpu). > > > > So you get rid of schedule(), the check for signal_pending, etc. > > But we'll still need to enter the guest when it's in a valid state, so > we need to move that loop somewhere, Sure, just set vmx->emulation_required = guest_state_valid(vcpu). When the state is good, the entry handler will vmentry. > and now that we still have a loop > we'll also still need to do the pending signals and scheduling checks, > no? Point is you can use the __vcpu_run loop. In the latest patch you do: + /* Don't enter VMX if guest state is invalid, let the exit handler + start emulation until we arrive back to a valid state */ + if (vmx->emulation_required && emulate_invalid_guest_state) return; And then emulate in the exit handler. > I'd appreciate any suggestions you have to alleviate this. I fail to see why you need an internal loop if you can use the external (__vcpu_run) one.