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Thu, 20 Feb 2020 13:08:38 +0000 (GMT) X-AuditID: cbfec7f2-ef1ff7000001ef66-23-5e4e84d68099 Received: from eusmtip2.samsung.com ( [203.254.199.222]) by eusmgms2.samsung.com (EUCPMTA) with SMTP id FC.D8.07950.6D48E4E5; Thu, 20 Feb 2020 13:08:38 +0000 (GMT) Received: from [106.120.51.71] (unknown [106.120.51.71]) by eusmtip2.samsung.com (KnoxPortal) with ESMTPA id 20200220130837eusmtip2b796955aa44da62ec7806b042c2a23f1~1HkMsM6K91020910209eusmtip2J; Thu, 20 Feb 2020 13:08:37 +0000 (GMT) Subject: Re: Re: [RFC PATCH 0/5] Removing support for 32bit KVM/arm host To: Marc Zyngier From: Bartlomiej Zolnierkiewicz Message-ID: <6b3a2e73-6c28-e25e-3375-692bdbd1d48b@samsung.com> Date: Thu, 20 Feb 2020 14:08:38 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20200219083113.52c1a8fb@why> Content-Language: en-US X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFprOKsWRmVeSWpSXmKPExsWy7djP87rXWvziDDb+UrT4sfM6o8Wmx9dY LdYeuctusXPOSVYHFo9NqzrZPDYvqffY83wZu0ffllWMASxRXDYpqTmZZalF+nYJXBkTlj9n KTgoVTHtbzdLA2O3aBcjJ4eEgInEu+bP7F2MXBxCAisYJb7s+QflfGGUuDljMzOE85lRYunJ vcwwLR933QKzhQSWM0osXqsPUfQWqGPuQVaQhLCAh8Sc1ffYQWwRAUWJTxdOMoLYzAL1Eov+ fgCLswlYSUxsXwUW5xWwk3i8ejdYnEVAVeLfh/tgtqhAhMSnB4dZIWoEJU7OfMICYnMKaEmc 3fyJGWKmuMStJ/OZIGx5ie1v54BdLSEwmV2iu+kPE8TVLhJrT89lh7CFJV4d3wJly0j83wnS DNKwjlHib8cLqO7tjBLLJ/9jg6iylrhz7heQzQG0QlNi/S59iLCjxOyvq5hBwhICfBI33gpC HMEnMWnbdKgwr0RHmxBEtZrEhmUb2GDWdu1cyTyBUWkWktdmIXlnFpJ3ZiHsXcDIsopRPLW0 ODc9tdgwL7Vcrzgxt7g0L10vOT93EyMwuZz+d/zTDsavl5IOMQpwMCrx8FY0+MUJsSaWFVfm HmKU4GBWEuFV4wEK8aYkVlalFuXHF5XmpBYfYpTmYFES5zVe9DJWSCA9sSQ1OzW1ILUIJsvE wSnVwGimZHVUr3zTTYfJE8JZ9Nd5l07TObh1umXi7xl1C/ebh+Z03KlZsm7tKXnnnHkOH182 27lY9bCEzAy8k8RZsaIm4aBlrP7f+sI9fsrypczSR/7UR/Ce/KXCHjNvUVN6Wlz01xMshxuD 5l1uPX3pReLGn58tVM62qF3t325Vuvlo3MRiv4MGUUosxRmJhlrMRcWJAGQMlZMqAwAA X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFlrBIsWRmVeSWpSXmKPExsVy+t/xe7rXWvziDN6+57P4sfM6o8Wmx9dY LdYeuctusXPOSVYHFo9NqzrZPDYvqffY83wZu0ffllWMASxRejZF+aUlqQoZ+cUltkrRhhZG eoaWFnpGJpZ6hsbmsVZGpkr6djYpqTmZZalF+nYJehkTlj9nKTgoVTHtbzdLA2O3aBcjJ4eE gInEx123mLsYuTiEBJYySux/1sjexcgBlJCROL6+DKJGWOLPtS42EFtI4DWjROvNGhBbWMBD Ys7qe+wgtoiAosSnCycZQWxmgXqJGb2T2CBmTmeUODP/AViCTcBKYmL7KjCbV8BO4vHq3WDN LAKqEv8+3AezRQUiJA7vmAVVIyhxcuYTFhCbU0BL4uzmT8wQC9Ql/sy7BGWLS9x6Mp8JwpaX 2P52DvMERqFZSNpnIWmZhaRlFpKWBYwsqxhFUkuLc9Nzi430ihNzi0vz0vWS83M3MQJjadux n1t2MHa9Cz7EKMDBqMTDW9HgFyfEmlhWXJl7iFGCg1lJhFeNByjEm5JYWZValB9fVJqTWnyI 0RTouYnMUqLJ+cA4zyuJNzQ1NLewNDQ3Njc2s1AS5+0QOBgjJJCeWJKanZpakFoE08fEwSnV wFiQkXMop2PR4j6lQ8ltq7+6mq25OL+aTea6hHHj7Hq+7YzHctc+41vEUCK6QE7y5XcGvr1v VtZpfZ0t7XO8Za+zb9Dbzzlcd9qY9h1+Yjj5cGuC9An3/ueJjNt2bT1pzi0Zo76abbFR0Jrj l8QFOdXcZ97kCm9e+mL9yh0vBNO/xnfq8xdNP6fEUpyRaKjFXFScCABz2bWfuwIAAA== X-CMS-MailID: 20200220130838eucas1p12bc652ecd882204a8ffda5ed28f48bd5 X-Msg-Generator: CA X-RootMTR: 20200220130838eucas1p12bc652ecd882204a8ffda5ed28f48bd5 X-EPHeader: CA CMS-TYPE: 201P X-CMS-RootMailID: 20200220130838eucas1p12bc652ecd882204a8ffda5ed28f48bd5 References: <20200218213712.GD1382@makrotopia.org> <20200219083113.52c1a8fb@why> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200220_050840_968575_16F1AACC X-CRM114-Status: GOOD ( 26.36 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Daniel Golle , linux-arm-kernel@lists.infradead.org, Marek Szyprowski Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Marc, On 2/19/20 9:31 AM, Marc Zyngier wrote: > On Tue, 18 Feb 2020 22:37:12 +0100 > Daniel Golle wrote: > > Daniel, > > Please keep people on cc, it helps with the discussion. > >>> Message-ID: <20200210141324.21090-1-maz@kernel.org> >>> >>> KVM/arm was merged just over 7 years ago, and has lived a very quiet >>> life so far. It mostly works if you're prepared to deal with its >>> limitations, it has been a good prototype for the arm64 version, >>> but it suffers a few problems: >>> >>> - It is incomplete (no debug support, no PMU) >>> - It hasn't followed any of the architectural evolutions >>> - It has zero users (I don't count myself here) >> >> Not true. At least I'm using KVM on CortexA7 (sun7i aka. Allwinner A20) >> and it has been quite useful until now (running low memory footprint >> OpenWrt-based guests on yocto/OpenEmbedded host) > > OK, so we have a user! We have also started using it recently (as described by Marek in https://lore.kernel.org/linux-arm-kernel/621a0a92-6432-6c3e-cb69-0b601764fa69@samsung.com/#t ). >>> - It is more and more getting in the way of new arm64 developments >> >> Can you elaborate more on how it is getting in the way? Just in terms >> of effort to maintain the necessary abstractions or does something >> really block ARM64 KVM support? > > Useless abstractions are indeed one of the problems. Essentially, > KVM/arm has become a pile of empty stubs that are added to make the > thing compile. This doesn't bode well for the future. > > The other aspect is that new features appearing on arm64 (nested virt, > enclaves, and potentially some more) are tearing the code-base apart, > and doing so while keeping 32bit alive and kicking would be a > challenge. I'm not saying it is impossible, just that it is hard, and > for very little gain, specially given that *nobody* contributes to the > port. I have very basic knowledge of virt/kvm/arm/ codebase (so my question may be quite stupid) but wouldn't it be possible to split the codebase into legacy virt/kvm/arm32/ and virt/kvm/arm64/ parts (this would cause some code duplication but at the same time would stop 32bit port from blocking new developments for 64bit one)? Best regards, -- Bartlomiej Zolnierkiewicz Samsung R&D Institute Poland Samsung Electronics >>> So here it is: unless someone screams and shows that they rely on >>> KVM/arm to be maintained upsteam, I'll remove 32bit host support >>> form the tree. One of the reasons that makes me confident nobody is >>> using it is that I never receive *any* bug report. Yes, it is perfect. >>> But if you depend on KVM/arm being available in mainline, please shout. >> >> I cetainly don't depend on it, meaning I'd have to replace hardware >> worth less than $100 in the near future, that's not too bad. >> And yes, it has just been working perfectly ;) > > I'm really glad it works well. Note that it isn't like we are taking it > away from you. 5.6 will still have it, and I will still maintain it as > part of the stable tree. It is just that I've come to the sad > conclusion that as a community, we need to move on. > > M. > > PS: and if you find a decent, reliable machine to replace your A20, > please let me know. All the arm64 SBCs I've seen are utter crap > compared to my Cubietruck... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel