From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9D392C43144 for ; Mon, 25 Jun 2018 16:05:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 62B0F25DB6 for ; Mon, 25 Jun 2018 16:05:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 62B0F25DB6 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932351AbeFYQFI (ORCPT ); Mon, 25 Jun 2018 12:05:08 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:53978 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754012AbeFYQFG (ORCPT ); Mon, 25 Jun 2018 12:05:06 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id B879EBF57C; Mon, 25 Jun 2018 16:05:05 +0000 (UTC) Received: from [10.36.112.27] (ovpn-112-27.ams2.redhat.com [10.36.112.27]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C5BEE2166B5D; Mon, 25 Jun 2018 16:05:02 +0000 (UTC) Subject: Re: [PATCH v2] kvm: x86: mmu: Add cast to negated bitmasks in update_permission_bitmask() To: Matthias Kaehlcke , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Thomas Gleixner , "H . Peter Anvin" Cc: x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Nick Desaulniers , Joe Perches References: <20180619192504.180479-1-mka@chromium.org> From: Paolo Bonzini Openpgp: preference=signencrypt Autocrypt: addr=pbonzini@redhat.com; prefer-encrypt=mutual; keydata= xsEhBFRCcBIBDqDGsz4K0zZun3jh+U6Z9wNGLKQ0kSFyjN38gMqU1SfP+TUNQepFHb/Gc0E2 CxXPkIBTvYY+ZPkoTh5xF9oS1jqI8iRLzouzF8yXs3QjQIZ2SfuCxSVwlV65jotcjD2FTN04 hVopm9llFijNZpVIOGUTqzM4U55sdsCcZUluWM6x4HSOdw5F5Utxfp1wOjD/v92Lrax0hjiX DResHSt48q+8FrZzY+AUbkUS+Jm34qjswdrgsC5uxeVcLkBgWLmov2kMaMROT0YmFY6A3m1S P/kXmHDXxhe23gKb3dgwxUTpENDBGcfEzrzilWueOeUWiOcWuFOed/C3SyijBx3Av/lbCsHU Vx6pMycNTdzU1BuAroB+Y3mNEuW56Yd44jlInzG2UOwt9XjjdKkJZ1g0P9dwptwLEgTEd3Fo UdhAQyRXGYO8oROiuh+RZ1lXp6AQ4ZjoyH8WLfTLf5g1EKCTc4C1sy1vQSdzIRu3rBIjAvnC tGZADei1IExLqB3uzXKzZ1BZ+Z8hnt2og9hb7H0y8diYfEk2w3R7wEr+Ehk5NQsT2MPI2QBd wEv1/Aj1DgUHZAHzG1QN9S8wNWQ6K9DqHZTBnI1hUlkp22zCSHK/6FwUCuYp1zcAEQEAAc0f UGFvbG8gQm9uemluaSA8Ym9uemluaUBnbnUub3JnPsLBTQQTAQIAIwUCVEJ7AwIbAwcLCQgH AwIBBhUIAgkKCwQWAgMBAh4BAheAAAoJEH4VEAzNNmmxNcwOniaZVLsuy1lW/ntYCA0Caz0i sHpmecK8aWlvL9wpQCk4GlOX9L1emyYXZPmzIYB0IRqmSzAlZxi+A2qm9XOxs5gJ2xqMEXX5 FMtUH3kpkWWJeLqe7z0EoQdUI4EG988uv/tdZyqjUn2XJE+K01x7r3MkUSFz/HZKZiCvYuze VlS0NTYdUt5jBXualvAwNKfxEkrxeHjxgdFHjYWhjflahY7TNRmuqPM/Lx7wAuyoDjlYNE40 Z+Kun4/KjMbjgpcF4Nf3PJQR8qXI6p3so2qsSn91tY7DFSJO6v2HwFJkC2jU95wxfNmTEUZc znXahYbVOwCDJRuPrE5GKFd/XJU9u5hNtr/uYipHij01WXal2cce1S5mn1/HuM1yo1u8xdHy IupCd57EWI948e8BlhpujUCU2tzOb2iYS0kpmJ9/oLVZrOcSZCcCl2P0AaCAsj59z2kwQS9D du0WxUs8waso0Qq6tDEHo8yLCOJDzSz4oojTtWe4zsulVnWV+wu70AioemAT8S6JOtlu60C5 dHgQUD1Tp+ReXpDKXmjbASJx4otvW0qah3o6JaqO79tbDqIvncu3tewwp6c85uZd48JnIOh3 utBAu684nJakbbvZUGikJfxd887ATQRUQnHuAQgAx4dxXO6/Zun0eVYOnr5GRl76+2UrAAem Vv9Yfn2PbDIbxXqLff7oyVJIkw4WdhQIIvvtu5zH24iYjmdfbg8iWpP7NqxUQRUZJEWbx2CR wkMHtOmzQiQ2tSLjKh/cHeyFH68xjeLcinR7jXMrHQK+UCEw6jqi1oeZzGvfmxarUmS0uRuf fAb589AJW50kkQK9VD/9QC2FJISSUDnRC0PawGSZDXhmvITJMdD4TjYrePYhSY4uuIV02v02 8TVAaYbIhxvDY0hUQE4r8ZbGRLn52bEzaIPgl1p/adKfeOUeMReg/CkyzQpmyB1TSk8lDMxQ zCYHXAzwnGi8WU9iuE1P0wARAQABwsEzBBgBAgAJBQJUQnHuAhsMAAoJEH4VEAzNNmmxp1EO oJy0uZggJm7gZKeJ7iUpeX4eqUtqelUw6gU2daz2hE/jsxsTbC/w5piHmk1H1VWDKEM4bQBT uiJ0bfo55SWsUNN+c9hhIX+Y8LEe22izK3w7mRpvGcg+/ZRG4DEMHLP6JVsv5GMpoYwYOmHn plOzCXHvmdlW0i6SrMsBDl9rw4AtIa6bRwWLim1lQ6EM3PWifPrWSUPrPcw4OLSwFk0CPqC4 HYv/7ZnASVkR5EERFF3+6iaaVi5OgBd81F1TCvCX2BEyIDRZLJNvX3TOd5FEN+lIrl26xecz 876SvcOb5SL5SKg9/rCBufdPSjojkGFWGziHiFaYhbuI2E+NfWLJtd+ZvWAAV+O0d8vFFSvr iy9enJ8kxJwhC0ECbSKFY+W1eTIhMD3aeAKY90drozWEyHhENf4l/V+Ja5vOnW+gCDQkGt2Y 1lJAPPSIqZKvHzGShdh8DduC0U3xYkfbGAUvbxeepjgzp0uEnBXfPTy09JGpgWbg0w91GyfT /ujKaGd4vxG2Ei+MMNDmS1SMx7wu0evvQ5kT9NPzyq8R2GIhVSiAd2jioGuTjX6AZCFv3ToO 53DliFMkVTecLptsXaesuUHgL9dKIfvpm+rNXRn9wAwGjk0X/A== Message-ID: <4dd99306-4fea-24b2-4bea-5b7927ea5e79@redhat.com> Date: Mon, 25 Jun 2018 18:05:01 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20180619192504.180479-1-mka@chromium.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Mon, 25 Jun 2018 16:05:05 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Mon, 25 Jun 2018 16:05:05 +0000 (UTC) for IP:'10.11.54.6' DOMAIN:'int-mx06.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'pbonzini@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19/06/2018 21:25, Matthias Kaehlcke wrote: > update_permission_bitmask() negates u8 bitmask values and assigns them > to variables of type u8. Since the MSB is set in the bitmask values the > compiler expands the negated values to int, which then is assigned to > an u8 variable. Cast the negated value back to u8. > > This fixes several warnings like this when building with clang: > > arch/x86/kvm/mmu.c:4266:39: error: implicit conversion from 'int' to 'u8' > (aka 'unsigned char') changes value from -205 to 51 [-Werror, > -Wconstant-conversion] > u8 wf = (pfec & PFERR_WRITE_MASK) ? ~w : 0; > ~~ ^~ > > (gcc also raises a warning (see https://godbolt.org/g/6JWfWk), however it > doesn't seem to be universally enabled) > > Suggested-by: Nick Desaulniers > Signed-off-by: Matthias Kaehlcke > --- > Changes in v2: > - negate the bitmask at initialization and rename variables to not_X The patch is not that bad, but I'd like to get confirmation that other maintainers are applying fixes like this. Honestly I'm not really impressed by most new clang warnings, these days. Paolo > arch/x86/kvm/mmu.c | 11 ++++++----- > 1 file changed, 6 insertions(+), 5 deletions(-) > > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > index d634f0332c0f..ad0a8c35f27b 100644 > --- a/arch/x86/kvm/mmu.c > +++ b/arch/x86/kvm/mmu.c > @@ -4258,8 +4258,9 @@ static void update_permission_bitmask(struct kvm_vcpu *vcpu, > { > unsigned byte; > > - const u8 x = BYTE_MASK(ACC_EXEC_MASK); > - const u8 w = BYTE_MASK(ACC_WRITE_MASK); > + const u8 not_x = (u8)~BYTE_MASK(ACC_EXEC_MASK); > + const u8 not_w = (u8)~BYTE_MASK(ACC_WRITE_MASK); > + const u8 not_u = (u8)~BYTE_MASK(ACC_USER_MASK); > const u8 u = BYTE_MASK(ACC_USER_MASK); > > bool cr4_smep = kvm_read_cr4_bits(vcpu, X86_CR4_SMEP) != 0; > @@ -4275,11 +4276,11 @@ static void update_permission_bitmask(struct kvm_vcpu *vcpu, > */ > > /* Faults from writes to non-writable pages */ > - u8 wf = (pfec & PFERR_WRITE_MASK) ? ~w : 0; > + u8 wf = (pfec & PFERR_WRITE_MASK) ? not_w : 0; > /* Faults from user mode accesses to supervisor pages */ > - u8 uf = (pfec & PFERR_USER_MASK) ? ~u : 0; > + u8 uf = (pfec & PFERR_USER_MASK) ? not_u : 0; > /* Faults from fetches of non-executable pages*/ > - u8 ff = (pfec & PFERR_FETCH_MASK) ? ~x : 0; > + u8 ff = (pfec & PFERR_FETCH_MASK) ? not_x : 0; > /* Faults from kernel mode fetches of user pages */ > u8 smepf = 0; > /* Faults from kernel mode accesses of user pages */ >