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=-10.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 CE24EC388F7 for ; Sun, 25 Oct 2020 09:52:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 711CF222C4 for ; Sun, 25 Oct 2020 09:52:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603619534; bh=oAXfvHzROiIAchD8Y3+9mWqjMiIAFBfr4ge5LH7qpEg=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=uSTl9Az9h31ZBrCY8uCNC8xp7oMVFDkvWlgyLHsMsIUyRYGyFPuf7KNJtXf2pXgw1 aHpaxKucqaVO3dP3bcowujOhNke+IQHZThL3Q/FW3iS5kye1ULjOnmGJj58NSoMEhT hZDFtyo3x58QO9dyunwbRoS0cUz+8fxCGoe67IoA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1414988AbgJYJwN (ORCPT ); Sun, 25 Oct 2020 05:52:13 -0400 Received: from mail.kernel.org ([198.145.29.99]:48968 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1414980AbgJYJwM (ORCPT ); Sun, 25 Oct 2020 05:52:12 -0400 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9CB5E22284; Sun, 25 Oct 2020 09:52:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603619531; bh=oAXfvHzROiIAchD8Y3+9mWqjMiIAFBfr4ge5LH7qpEg=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=0Sciwr7fKR4KR1rr5vJ8UDM0uTOSzPJ49v+93GOdbuMF1bhiMIt0qT0UaxXdhzuH1 aTjfMKWaTgHjUCHwMpbn8THNc7F7aGkfi6H+W5+KCrUEkKSlidVTOwYlq/iIY/ZcaP CmjOzW1NRC1tDUzWrv3wX5sxqFn1jlxnc5wt0NCs= Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=wait-a-minute.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1kWch7-0041v2-I6; Sun, 25 Oct 2020 09:52:09 +0000 Date: Sun, 25 Oct 2020 09:52:09 +0000 Message-ID: <871rhmpr92.wl-maz@kernel.org> From: Marc Zyngier To: Gavin Shan Cc: kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, will@kernel.org, alexandru.elisei@arm.com Subject: Re: [PATCH 1/3] KVM: arm64: Check if 52-bits PA is enabled In-Reply-To: <20201025002739.5804-2-gshan@redhat.com> References: <20201025002739.5804-1-gshan@redhat.com> <20201025002739.5804-2-gshan@redhat.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.8 EasyPG/1.0.0 Emacs/26.3 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: gshan@redhat.com, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, will@kernel.org, alexandru.elisei@arm.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 25 Oct 2020 01:27:37 +0100, Gavin Shan wrote: > > The 52-bits physical address is disabled until CONFIG_ARM64_PA_BITS_52 > is chosen. This uses option for that check, to avoid the unconditional > check on PAGE_SHIFT in the hot path and thus save some CPU cycles. PAGE_SHIFT is known at compile time, and this code is dropped by the compiler if the selected page size is not 64K. This patch really only makes the code slightly less readable and the "CPU cycles" argument doesn't hold at all. So what are you trying to solve exactly? M. > > Signed-off-by: Gavin Shan > --- > arch/arm64/kvm/hyp/pgtable.c | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c > index 0cdf6e461cbd..fd850353ee89 100644 > --- a/arch/arm64/kvm/hyp/pgtable.c > +++ b/arch/arm64/kvm/hyp/pgtable.c > @@ -132,8 +132,9 @@ static u64 kvm_pte_to_phys(kvm_pte_t pte) > { > u64 pa = pte & KVM_PTE_ADDR_MASK; > > - if (PAGE_SHIFT == 16) > - pa |= FIELD_GET(KVM_PTE_ADDR_51_48, pte) << 48; > +#ifdef CONFIG_ARM64_PA_BITS_52 > + pa |= FIELD_GET(KVM_PTE_ADDR_51_48, pte) << 48; > +#endif > > return pa; > } > @@ -142,8 +143,9 @@ static kvm_pte_t kvm_phys_to_pte(u64 pa) > { > kvm_pte_t pte = pa & KVM_PTE_ADDR_MASK; > > - if (PAGE_SHIFT == 16) > - pte |= FIELD_PREP(KVM_PTE_ADDR_51_48, pa >> 48); > +#ifdef CONFIG_ARM64_PA_BITS_52 > + pte |= FIELD_PREP(KVM_PTE_ADDR_51_48, pa >> 48); > +#endif > > return pte; > } > -- > 2.23.0 > > -- Without deviation from the norm, progress is not possible.