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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id C6152C64EC4 for ; Thu, 9 Mar 2023 08:26:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Subject:Cc:To:From:Message-ID:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=47MswE8PhVWu/5SOZ9la9/wQIkChmbcl8ekOCvlfSCQ=; b=J/QInMLAfikCMW UCABr/yt8ky0u8mx4vHoAuJvgFunRmGAlSuzbeAjBm42/sWJbPPZEQTCV4kOrZoOdDosfBHW1QwMz IVKg4d/BOurLNPDVaH0PhLdrYRn4UJTXS8/65/XOxke/rQim6YuPs2J8LhsesyNeEN43kKtDmmydx HWovelalHUvOVKgMraVgL7teGd0zP3760O96cM7DhXVrgojiwlskiWspnobG+Wjpfl7NeMb1ht7jP AZh2dE/WlKxr7iXjwT9nQJEJP5po7/QL8AYkNz6sOLJzEQHcdlG6zLhgHBh13xVBQh7n2DCkB7NZo I2hSjCiGKmjIguMkfKVA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1paBaZ-008VRT-53; Thu, 09 Mar 2023 08:25:27 +0000 Received: from dfw.source.kernel.org ([2604:1380:4641:c500::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1paBaV-008VPy-P7 for linux-arm-kernel@lists.infradead.org; Thu, 09 Mar 2023 08:25:25 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 3833761A38; Thu, 9 Mar 2023 08:25:23 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9F99DC433D2; Thu, 9 Mar 2023 08:25:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1678350322; bh=NF9uArR2Xw5L2IGuaa/g8Rp3bnNLsfYmX4k/kLHf5dU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=HIZkDW+ZobbMS8sY2RQce3TyaEsk0+/Pa6CZynJWokaSN631tYMqs0ugi+d4YL4Ik cQ1R6giTTL6Y2y/wOd5rP4wV9UpnHxjSfDFdD98u4slejiz70gBCA75KYR50owz3Zd 6ih+k8lhyqwqI1t5Yx/ZnBJMB9NIxgAfQWkSrdqLazPoTOPKMZAwMZqHL2ne5cA92U pw1nO3rzR6m2DzYl+bDZ+8wjaFxMfUBtK7WswNIKoWShgEgaBpVmImwZv0asqn3qSL GmzL9FhvRh68kiclt5uZzRdP1NAJl77WqOkTyexORSxZmrcK83iF3lBLRK4IDMIK/h QpHQ4aAXcbm0Q== Received: from 82-132-236-50.dab.02.net ([82.132.236.50] helo=wait-a-minute.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1paBaM-00GFDI-SY; Thu, 09 Mar 2023 08:25:15 +0000 Date: Thu, 09 Mar 2023 08:25:09 +0000 Message-ID: <87edpy9vru.wl-maz@kernel.org> From: Marc Zyngier To: Oliver Upton Cc: kvmarm@lists.linux.dev, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, James Morse , Suzuki K Poulose , Zenghui Yu , Ricardo Koller , Simon Veith , dwmw2@infradead.org Subject: Re: [PATCH 08/16] KVM: arm64: timers: Allow userspace to set the counter offsets In-Reply-To: References: <20230216142123.2638675-1-maz@kernel.org> <20230216142123.2638675-9-maz@kernel.org> <86k00gy4so.wl-maz@kernel.org> <86bkllyku2.wl-maz@kernel.org> <867cw8xmq2.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") X-SA-Exim-Connect-IP: 82.132.236.50 X-SA-Exim-Rcpt-To: oliver.upton@linux.dev, kvmarm@lists.linux.dev, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, james.morse@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, ricarkol@google.com, sveith@amazon.de, dwmw2@infradead.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230309_002523_910474_8626E2A3 X-CRM114-Status: GOOD ( 16.48 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Oliver, On Wed, 08 Mar 2023 07:46:00 +0000, Oliver Upton wrote: [...] > I certainly agree that (2a) is highly desirable to get existing VMMs to > 'do the right thing' for free. Playing devil's advocate, would this not > also break the tracing example you've given of correlating timestamps > between the host and guest? I wouldn't expect a userspace + VM tracing > contraption to live migrate but restoring from a snapshot seems > plausible. It really depends when this VM was saved. If you saved it on an old host that doesn't expose CNTPCT and restore it on a new host, the physical offset is still zero (this is already special-cased), and there is no difference in behaviour. If you saved it from a host that does expose CNTPCT, then the behaviour changes. But should we really care? > Regardless, I like the general direction you've proposed. IIUC, you'll > want to go ahead with ignoring writes to CNT{P,V}CT if the offset was > written by userspace, right? That'd be my preference in order not to break the "blind restore" behaviour that QEMU already uses for about everything. I'll repost the series shortly, as it has grown some extra goodies such as moving the PPI settings out of the way... Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel