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charset="UTF-8" On Fri, 19 Apr 2024 at 18:08, Will Deacon wrote: > > On Thu, Apr 11, 2024 at 11:19:13PM +0900, Hector Martin wrote: > > On 2024/04/11 22:28, Will Deacon wrote: > > > * Some binaries in a distribution exhibit instability which goes away > > > in TSO mode, so a taskset-like program is used to run them with TSO > > > enabled. > > > > Since the flag is cleared on execve, this third one isn't generally > > possible as far as I know. > > Ah ok, I'd missed that. Thanks. > > > > In all these cases, we end up with native arm64 applications that will > > > either fail to load or will crash in subtle ways on CPUs without the TSO > > > feature. Assuming that the application cannot be fixed, a better > > > approach would be to recompile using stronger instructions (e.g. > > > LDAR/STLR) so that at least the resulting binary is portable. Now, it's > > > true that some existing CPUs are TSO by design (this is a perfectly > > > valid implementation of the arm64 memory model), but I think there's a > > > big difference between quietly providing more ordering guarantees than > > > software may be relying on and providing a mechanism to discover, > > > request and ultimately rely upon the stronger behaviour. > > > > The problem is "just" using stronger instructions is much more > > expensive, as emulators have demonstrated. If TSO didn't serve a > > practical purpose I wouldn't be submitting this, but it does. This is > > basically non-negotiable for x86 emulation; if this is rejected > > upstream, it will forever live as a downstream patch used by the entire > > gaming-on-Mac-Linux ecosystem (and this is an ecosystem we are very > > explicitly targeting, given our efforts with microVMs for 4K page size > > support and the upcoming Vulkan drivers). > > These microVMs sound quite interesting. What exactly are they? Are you > running them under KVM? It's the magic of libkrun. This is one of the git repos in the family of libkrun, it has a wide array of use cases, which I personally won't do much justice explaining all then, this is just one repo/tool/usecases: https://github.com/containers/krunvm https://sinrega.org/running-microvms-on-m1/ CC'ing @Sergio Lopez Pascual the lead of krun in general. Is mise le meas/Regards, Eric Curtin > > Ignoring the mechanism for the time being, would it solve your problem > if you were able to run specific microVMs in TSO mode, or do you *really* > need the VM to have finer-grained control than that? If the whole VM is > running in TSO mode, then my concerns largely disappear, as that's > indistinguishable from running on a hardware implementation that happens > to be TSO. > > > That said, I have a pragmatic proposal here. The "fixed TSO" part of the > > implementation should be harmless, since those CPUs would correctly run > > poorly-written applications anyway so the API is moot. That leaves Apple > > Silicon. Our native kernels are and likely always will be 16K page size, > > due to a bunch of pain around 16K-only IOMMUs (4K kernels do boot > > natively but with very broken functionality including no GPU > > acceleration) plus performance differences that favor 16K. How about we > > gate the TSO functionality to only be supported on 4K kernel builds? > > This would make them only work in 4K VMs on Asahi Linux. We are very > > explicitly discouraging people from trying to use the microVMs to work > > around page size problems (which they can already do, another > > fragmentation problem, anyway); any application which requires the 4K VM > > to run that isn't an emulator is already clearly broken and advertising > > that fact openly. So, adding TSO to this should be only a marginal risk > > of further fragmentation, and it wouldn't allow apps to "sneakily" "just > > work" on Apple machines by abusing TSO. > > I appreciate that you're trying to be constructive here, but I don't think > we should tie this to the page size. It's an artifical limitation and I > don't think it really addresses the underlying concerns that I have. > > Will > 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 51BD0C4345F for ; Sat, 20 Apr 2024 12:16:25 +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:Cc:To:Subject:Message-ID:Date:From: In-Reply-To:References:MIME-Version:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=/xiGaiXkIV3RUDiUuMz+vRrFVsxZvtDvTz9GsI7emwg=; 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AJvYcCWfdU0BwfbvjuENflam6qyxhytjZvDjJ8YoGGn90bqJQ0xn4nUt7gD4d3OG3CJ2/C4zh6TlcCIKmwgkfWVbjuvE5jKAmpg1eXhC0UHl4fiSULTjtCM= X-Gm-Message-State: AOJu0YyVG1A7rC4SPBR8c1b56PyeTPx38dNDFHKd8YlrnTJcc6Vvw4f6 xCybeKBBtvGsLJ6Y6OECxXj/PQQF8gz7vFGcDK8nCZx+1ZH4occKLc4U0g8Zk5j7qP5ii9VkST3 kzbaEbnWoIjv2Y5pVhWZJjFjIjB1xWsTAfXWL0gjBUViS7llRAYLxUdXf5EOynPO0Uu3XBTdh0h jHRLl5yrKhLznSkhkPDVaK2N+6FilOhLro61EMbRG+8NOeJS8= X-Received: by 2002:a17:90b:4f8f:b0:2a0:9b66:8e22 with SMTP id qe15-20020a17090b4f8f00b002a09b668e22mr3868929pjb.24.1713615254968; Sat, 20 Apr 2024 05:14:14 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHsHuOB/oNQk6rhvlabCIKccBuvsNSSpeF7mDscQ/D/nU4o7qvI+9aQIV6/VOpH63JMXbU3K2Hm1ot18E6cj9A= X-Received: by 2002:a17:90b:4f8f:b0:2a0:9b66:8e22 with SMTP id qe15-20020a17090b4f8f00b002a09b668e22mr3868910pjb.24.1713615254613; Sat, 20 Apr 2024 05:14:14 -0700 (PDT) MIME-Version: 1.0 References: <20240411-tso-v1-0-754f11abfbff@marcan.st> <20240411132853.GA26481@willie-the-truck> <28ab55b3-e699-4487-b332-f1f20a6b22a1@marcan.st> <20240419165809.GA4020@willie-the-truck> In-Reply-To: <20240419165809.GA4020@willie-the-truck> From: Eric Curtin Date: Sat, 20 Apr 2024 13:13:38 +0100 Message-ID: Subject: Re: [PATCH 0/4] arm64: Support the TSO memory model To: Will Deacon Cc: Hector Martin , Catalin Marinas , Marc Zyngier , Mark Rutland , Zayd Qumsieh , Justin Lu , Ryan Houdek , Mark Brown , Ard Biesheuvel , Mateusz Guzik , Anshuman Khandual , Oliver Upton , Miguel Luis , Joey Gouly , Christoph Paasch , Kees Cook , Sami Tolvanen , Baoquan He , Joel Granados , Dawei Li , Andrew Morton , Florent Revest , David Hildenbrand , Stefan Roesch , Andy Chiu , Josh Triplett , Oleg Nesterov , Helge Deller , Zev Weiss , Ondrej Mosnacek , Miguel Ojeda , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Asahi Linux , Sergio Lopez Pascual X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240420_051606_178744_9701484C X-CRM114-Status: GOOD ( 38.92 ) 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 On Fri, 19 Apr 2024 at 18:08, Will Deacon wrote: > > On Thu, Apr 11, 2024 at 11:19:13PM +0900, Hector Martin wrote: > > On 2024/04/11 22:28, Will Deacon wrote: > > > * Some binaries in a distribution exhibit instability which goes away > > > in TSO mode, so a taskset-like program is used to run them with TSO > > > enabled. > > > > Since the flag is cleared on execve, this third one isn't generally > > possible as far as I know. > > Ah ok, I'd missed that. Thanks. > > > > In all these cases, we end up with native arm64 applications that will > > > either fail to load or will crash in subtle ways on CPUs without the TSO > > > feature. Assuming that the application cannot be fixed, a better > > > approach would be to recompile using stronger instructions (e.g. > > > LDAR/STLR) so that at least the resulting binary is portable. Now, it's > > > true that some existing CPUs are TSO by design (this is a perfectly > > > valid implementation of the arm64 memory model), but I think there's a > > > big difference between quietly providing more ordering guarantees than > > > software may be relying on and providing a mechanism to discover, > > > request and ultimately rely upon the stronger behaviour. > > > > The problem is "just" using stronger instructions is much more > > expensive, as emulators have demonstrated. If TSO didn't serve a > > practical purpose I wouldn't be submitting this, but it does. This is > > basically non-negotiable for x86 emulation; if this is rejected > > upstream, it will forever live as a downstream patch used by the entire > > gaming-on-Mac-Linux ecosystem (and this is an ecosystem we are very > > explicitly targeting, given our efforts with microVMs for 4K page size > > support and the upcoming Vulkan drivers). > > These microVMs sound quite interesting. What exactly are they? Are you > running them under KVM? It's the magic of libkrun. This is one of the git repos in the family of libkrun, it has a wide array of use cases, which I personally won't do much justice explaining all then, this is just one repo/tool/usecases: https://github.com/containers/krunvm https://sinrega.org/running-microvms-on-m1/ CC'ing @Sergio Lopez Pascual the lead of krun in general. Is mise le meas/Regards, Eric Curtin > > Ignoring the mechanism for the time being, would it solve your problem > if you were able to run specific microVMs in TSO mode, or do you *really* > need the VM to have finer-grained control than that? If the whole VM is > running in TSO mode, then my concerns largely disappear, as that's > indistinguishable from running on a hardware implementation that happens > to be TSO. > > > That said, I have a pragmatic proposal here. The "fixed TSO" part of the > > implementation should be harmless, since those CPUs would correctly run > > poorly-written applications anyway so the API is moot. That leaves Apple > > Silicon. Our native kernels are and likely always will be 16K page size, > > due to a bunch of pain around 16K-only IOMMUs (4K kernels do boot > > natively but with very broken functionality including no GPU > > acceleration) plus performance differences that favor 16K. How about we > > gate the TSO functionality to only be supported on 4K kernel builds? > > This would make them only work in 4K VMs on Asahi Linux. We are very > > explicitly discouraging people from trying to use the microVMs to work > > around page size problems (which they can already do, another > > fragmentation problem, anyway); any application which requires the 4K VM > > to run that isn't an emulator is already clearly broken and advertising > > that fact openly. So, adding TSO to this should be only a marginal risk > > of further fragmentation, and it wouldn't allow apps to "sneakily" "just > > work" on Apple machines by abusing TSO. > > I appreciate that you're trying to be constructive here, but I don't think > we should tie this to the page size. It's an artifical limitation and I > don't think it really addresses the underlying concerns that I have. > > Will > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel