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=-4.0 required=3.0 tests=BAYES_00,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 949CEC433E1 for ; Tue, 30 Mar 2021 14:00:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5F2846044F for ; Tue, 30 Mar 2021 14:00:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232174AbhC3OA2 (ORCPT ); Tue, 30 Mar 2021 10:00:28 -0400 Received: from mail.kernel.org ([198.145.29.99]:37612 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231910AbhC3OAT (ORCPT ); Tue, 30 Mar 2021 10:00:19 -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 020996044F; Tue, 30 Mar 2021 14:00:19 +0000 (UTC) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] 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) (envelope-from ) id 1lREum-004h4b-Tm; Tue, 30 Mar 2021 15:00:17 +0100 Date: Tue, 30 Mar 2021 15:00:16 +0100 Message-ID: <87ft0crbbj.wl-maz@kernel.org> From: Marc Zyngier To: Suzuki K Poulose Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, coresight@lists.linaro.org, mathieu.poirier@linaro.org, mike.leach@linaro.org, leo.yan@linaro.org, anshuman.khandual@arm.com, catalin.marinas@arm.com, Will Deacon , Mark Rutland , Alexandru Elisei Subject: Re: [PATCH v5 07/19] arm64: kvm: Enable access to TRBE support for host In-Reply-To: References: <20210323120647.454211-1-suzuki.poulose@arm.com> <20210323120647.454211-8-suzuki.poulose@arm.com> <87r1jxq7ax.wl-maz@kernel.org> <87mtukrg6o.wl-maz@kernel.org> 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: 62.31.163.78 X-SA-Exim-Rcpt-To: suzuki.poulose@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, coresight@lists.linaro.org, mathieu.poirier@linaro.org, mike.leach@linaro.org, leo.yan@linaro.org, anshuman.khandual@arm.com, catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, 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 Tue, 30 Mar 2021 14:34:23 +0100, Suzuki K Poulose wrote: > > On 30/03/2021 13:15, Marc Zyngier wrote: > > On Tue, 30 Mar 2021 12:12:49 +0100, > > Suzuki K Poulose wrote: [...] > >> May be we could do this check at kvm_arch_vcpu_load()/put() ? > > > > That would extend the tracing blackout period enormously, wouldn't it? > > I'm not sure that's the best thing to do... > > Sorry for not making this clear. We could check if the SPE/TRBE is > available on this CPU (including the PMB/TRB_IDR bits and a set a flag > in the VCPU on every kvm_arch_vcpu_load() and cleared on put. > The actual switching code could check this flag and check if the unit > is enabled and then do the actual save/restore as we do below. > (We may be able to even check if unit is enabled there, need to double > check this.) Ah, gotcha. Yes, this seems like a reasonable thing to do. We have the per-vcpu debug flags already, and you could piggy-back on that. Thanks, M. -- Without deviation from the norm, progress is not possible.