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=-9.0 required=3.0 tests=BAYES_00,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,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 24059C07E94 for ; Fri, 4 Jun 2021 13:54:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F07F861405 for ; Fri, 4 Jun 2021 13:54:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230424AbhFDN42 (ORCPT ); Fri, 4 Jun 2021 09:56:28 -0400 Received: from mail.kernel.org ([198.145.29.99]:34816 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230209AbhFDN40 (ORCPT ); Fri, 4 Jun 2021 09:56:26 -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 6F33F613F3; Fri, 4 Jun 2021 13:54:40 +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 4.94.2) (envelope-from ) id 1lpAHV-005UZU-Tf; Fri, 04 Jun 2021 14:54:38 +0100 Date: Fri, 04 Jun 2021 14:54:37 +0100 Message-ID: <87sg1xzqea.wl-maz@kernel.org> From: Marc Zyngier To: Shameerali Kolothum Thodi Cc: "linux-arm-kernel@lists.infradead.org" , "kvmarm@lists.cs.columbia.edu" , "linux-kernel@vger.kernel.org" , "will@kernel.org" , "catalin.marinas@arm.com" , "james.morse@arm.com" , "julien.thierry.kdev@gmail.com" , "suzuki.poulose@arm.com" , "jean-philippe@linaro.org" , Alexandru Elisei , Linuxarm Subject: Re: [RFC PATCH 0/3] kvm/arm: New VMID allocator based on asid(2nd approach) In-Reply-To: References: <20210506165232.1969-1-shameerali.kolothum.thodi@huawei.com> 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: shameerali.kolothum.thodi@huawei.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, will@kernel.org, catalin.marinas@arm.com, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, jean-philippe@linaro.org, Alexandru.Elisei@arm.com, linuxarm@huawei.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 Fri, 04 Jun 2021 09:13:10 +0100, Shameerali Kolothum Thodi wrote: > > Hi, > > > -----Original Message----- > > From: Shameerali Kolothum Thodi > > Sent: 06 May 2021 17:52 > > To: linux-arm-kernel@lists.infradead.org; kvmarm@lists.cs.columbia.edu; > > linux-kernel@vger.kernel.org > > Cc: maz@kernel.org; will@kernel.org; catalin.marinas@arm.com; > > james.morse@arm.com; julien.thierry.kdev@gmail.com; > > suzuki.poulose@arm.com; jean-philippe@linaro.org; Linuxarm > > > > Subject: [RFC PATCH 0/3] kvm/arm: New VMID allocator based on asid(2nd > > approach) > > > > This is based on a suggestion from Will [0] to try out the asid > > based kvm vmid solution as a separate VMID allocator instead of > > the shared lib approach attempted in v4[1]. > > > > The idea is to compare both the approaches and see whether the > > shared lib solution with callbacks make sense or not. > > A gentle ping on this. Please take a look and let me know. I had a look and I don't overly dislike it. I'd like to see the code without the pinned stuff though, at least to ease the reviewing. I haven't tested it in anger, but I have pushed the rebased code at [1] as it really didn't apply to 5.13-rc4. One thing I'm a bit worried about is that we so far relied on VMID 0 never being allocated to a guest, which is now crucial for protected KVM. I can't really convince myself that this can never happen with this. Plus, I've found this nugget: What is this "- 2"? My hunch is that it should really be "- 1" as VMID 0 is reserved, and we have no equivalent of KPTI for S2. M. [1] https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=kvm-arm64/mmu/vmid -- Without deviation from the norm, progress is not possible.