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=-14.0 required=3.0 tests=BAYES_00,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,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 74A5CC4338F for ; Wed, 28 Jul 2021 09:41:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4CBDB60FC2 for ; Wed, 28 Jul 2021 09:41:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235396AbhG1JlF (ORCPT ); Wed, 28 Jul 2021 05:41:05 -0400 Received: from mail.kernel.org ([198.145.29.99]:52636 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231408AbhG1JlE (ORCPT ); Wed, 28 Jul 2021 05:41:04 -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 50B6260F9C; Wed, 28 Jul 2021 09:41:03 +0000 (UTC) Received: from sofa.misterjones.org ([185.219.108.64] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1m8g3h-001Uxw-D0; Wed, 28 Jul 2021 10:41:01 +0100 Date: Wed, 28 Jul 2021 10:41:00 +0100 Message-ID: <875ywuepxv.wl-maz@kernel.org> From: Marc Zyngier To: Will Deacon Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, qperret@google.com, dbrazdil@google.com, Srivatsa Vaddagiri , Shanker R Donthineni , James Morse , Suzuki K Poulose , Alexandru Elisei , kernel-team@android.com Subject: Re: [PATCH 01/16] KVM: arm64: Generalise VM features into a set of flags In-Reply-To: <20210727181026.GA19173@willie-the-truck> References: <20210715163159.1480168-1-maz@kernel.org> <20210715163159.1480168-2-maz@kernel.org> <20210727181026.GA19173@willie-the-truck> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (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: 185.219.108.64 X-SA-Exim-Rcpt-To: will@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, qperret@google.com, dbrazdil@google.com, vatsa@codeaurora.org, sdonthineni@nvidia.com, james.morse@arm.com, suzuki.poulose@arm.com, alexandru.elisei@arm.com, kernel-team@android.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: kvm@vger.kernel.org On Tue, 27 Jul 2021 19:10:27 +0100, Will Deacon wrote: > > On Thu, Jul 15, 2021 at 05:31:44PM +0100, Marc Zyngier wrote: > > We currently deal with a set of booleans for VM features, > > while they could be better represented as set of flags > > contained in an unsigned long, similarily to what we are > > doing on the CPU side. > > > > Signed-off-by: Marc Zyngier > > --- > > arch/arm64/include/asm/kvm_host.h | 12 +++++++----- > > arch/arm64/kvm/arm.c | 5 +++-- > > arch/arm64/kvm/mmio.c | 3 ++- > > 3 files changed, 12 insertions(+), 8 deletions(-) > > > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h > > index 41911585ae0c..4add6c27251f 100644 > > --- a/arch/arm64/include/asm/kvm_host.h > > +++ b/arch/arm64/include/asm/kvm_host.h > > @@ -122,7 +122,10 @@ struct kvm_arch { > > * should) opt in to this feature if KVM_CAP_ARM_NISV_TO_USER is > > * supported. > > */ > > - bool return_nisv_io_abort_to_user; > > +#define KVM_ARCH_FLAG_RETURN_NISV_IO_ABORT_TO_USER 0 > > + /* Memory Tagging Extension enabled for the guest */ > > +#define KVM_ARCH_FLAG_MTE_ENABLED 1 > > + unsigned long flags; > > One downside of packing all these together is that updating 'flags' now > requires an atomic rmw sequence (i.e. set_bit()). Then again, that's > probably for the best anyway given that kvm_vm_ioctl_enable_cap() looks > like it doesn't hold any locks. That, and these operations are supposed to be extremely rare anyway. > > > /* > > * VM-wide PMU filter, implemented as a bitmap and big enough for > > @@ -133,9 +136,6 @@ struct kvm_arch { > > > > u8 pfr0_csv2; > > u8 pfr0_csv3; > > - > > - /* Memory Tagging Extension enabled for the guest */ > > - bool mte_enabled; > > }; > > > > struct kvm_vcpu_fault_info { > > @@ -777,7 +777,9 @@ bool kvm_arm_vcpu_is_finalized(struct kvm_vcpu *vcpu); > > #define kvm_arm_vcpu_sve_finalized(vcpu) \ > > ((vcpu)->arch.flags & KVM_ARM64_VCPU_SVE_FINALIZED) > > > > -#define kvm_has_mte(kvm) (system_supports_mte() && (kvm)->arch.mte_enabled) > > +#define kvm_has_mte(kvm) \ > > + (system_supports_mte() && \ > > + test_bit(KVM_ARCH_FLAG_MTE_ENABLED, &(kvm)->arch.flags)) > > Not an issue with this patch, but I just noticed that the > system_supports_mte() check is redundant here as we only allow the flag to > be set if that's already the case. It allows us to save a memory access if system_supports_mte() is false (it is eventually implemented as a static key). On the other hand, there is so much inlining due to it being a non-final cap that we probably lose on that too... M. -- Without deviation from the norm, progress is not possible.