From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751916AbcGNSwh (ORCPT ); Thu, 14 Jul 2016 14:52:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36945 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751119AbcGNSwe (ORCPT ); Thu, 14 Jul 2016 14:52:34 -0400 From: Bandan Das To: Paolo Bonzini Cc: kvm@vger.kernel.org, guangrong.xiao@linux.intel.com, kernellwp@gmail.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 0/5] Add support for EPT execute only for nested hypervisors References: <1468361932-16580-1-git-send-email-bsd@redhat.com> <82db70ed-761e-0377-5417-acb64bed6cb6@redhat.com> <921eef54-f23b-cd90-8e20-a428a00a3297@redhat.com> <26006044-7096-63e5-8156-a15f001d8403@redhat.com> <5951c0e5-4c41-4817-034a-5214a10cf53c@redhat.com> Date: Thu, 14 Jul 2016 14:52:32 -0400 In-Reply-To: <5951c0e5-4c41-4817-034a-5214a10cf53c@redhat.com> (Paolo Bonzini's message of "Thu, 14 Jul 2016 20:29:25 +0200") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Thu, 14 Jul 2016 18:52:33 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Paolo Bonzini writes: > On 14/07/2016 19:38, Bandan Das wrote: >> Paolo Bonzini writes: >> >>> On 13/07/2016 17:47, Bandan Das wrote: >>>>>> I wanted to keep it the former way because "PT_PRESENT_MASK is equal to VMX_EPT_READABLE_MASK" >>>>>> is an assumption all throughout. I wanted to use this section to catch mismatches. >>>>> >>>>> I think there's no such assumption anymore, actually. Can you double >>>>> check? If there are any, that's where the BUILD_BUG_ON should be. >>>> >>>> What I meant is how they are the same bit. is_shadow_present_pte() is probably one >>>> and another one is link_shadow_page() which already has a BUILD_BUG_ON(). >>> >>> You're right about link_shadow_page()! We probably should change the >>> PT_PRESENT_MASK to shadow_present_mask there (and then readability in >>> the EPT execonly case is still provided by shadow_user_mask). >> >> Makes sense. Would you like a new version with that added or can that be a >> separate patch ? > > I've already done it and pushed it to kvm/next. :) Ah, thank you! >>> For is_shadow_present_pte() you have removed it in patch 1 though. >> >> Right. But the assumption is still that is_shadow_present_pte() works because >> EPT_READABLE and PT_PRESENT are the same. > > is_shadow_present_pte() tests 0xFFFFFFFF, so it does not depend on bit 0 > alone, for neither EPT nor "normal" page tables. Yeah... Let me rephrase, is_shadow_present_pte works because the assumption is that both of the bits are in the first 32 bits :) You proved me wrong though, this assumption does not mean a BUILD_BUG for the equal condition is required here. Bandan > Paolo