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 3CD05D5E39B for ; Sun, 10 Nov 2024 11:08:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Type:MIME-Version: References:In-Reply-To:Subject:Cc:To:From:Message-ID:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Hqc7NlHddbr417Na2OOag5t9VNKv96dvGbmazjRMJww=; b=h4jOvSou18H5vvgyyLLk9hfVqt KEmTOYuCP7b67juzxrJDvFHi6wy0ezX6fiuUjxlAYzTNoFcIIE3/4Y2/2cIEwq7Bo47o+WO3MMsZR FK4JDWa3vItpaUWSCuIm/khZoyeHa6vXrxreBk0jMCd758dziNcKCcS6T4D9QHN3WiGx24LyZsXVQ /7GOEhEDZM/fYSoCCmu83ebesb024KRfXndmdHmlP+vDjuaqeF7VOV54cvGBDVQf0DD6U9LrlTZPu WVWx2JKcGhV1zhQIjzAjCF7QUWZTU4crnUBrpY+G6Y1sxMSaeNPKQejSPqm8qceu3xqAC6dWPG8sc X4kRb/YA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tA5nS-0000000EjuN-2Pzj; Sun, 10 Nov 2024 11:07:58 +0000 Received: from nyc.source.kernel.org ([147.75.193.91]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1tA5lc-0000000Ejkv-1EM1 for linux-arm-kernel@lists.infradead.org; Sun, 10 Nov 2024 11:06:10 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by nyc.source.kernel.org (Postfix) with ESMTP id F32CBA40BFC; Sun, 10 Nov 2024 11:04:07 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id ED048C4CECD; Sun, 10 Nov 2024 11:06:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1731236762; bh=JrSQGG15LXh7EHM9jxGHjoA+82yehZX3lpYcI5Ku6v4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=D1EtzCi/bDRvyIgaRgcAfws07iy4lKS6mN/vD2uwMehNvZwBt1LTmnOP+1msGahjT 43eKrHmUsVXkAUOTqnc2waCweK/vp0m+SBByaJdqjMghe9Xl9Q/aK+VoJqFDLaFxSV TDZ+UCi1shXr879YkxkUWWl0ZM4Msp0PzpWsU8vg8ltWQ0ZF30xmZ2WgLVfLCMgxK7 e3XZ2q1nAtzH9i+WJwk2lhsXVdvrX/C0w/0r7wLUuYHaUwc6Btqx/OXdEOzcqbn91X ElmPCvrx2uWNf2Ylheq6TUQpm9mpO/PTSAVkZYTTYFS5uxOYAZWWfkbB6jGIsQCoxv gdar6IyuncQ7A== Received: from sofa.misterjones.org ([185.219.108.64] helo=goblin-girl.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 1tA5lX-00BbDn-AP; Sun, 10 Nov 2024 11:05:59 +0000 Date: Sun, 10 Nov 2024 11:05:58 +0000 Message-ID: <86r07jz6uh.wl-maz@kernel.org> From: Marc Zyngier To: Kalesh Singh Cc: will@kernel.org, qperret@google.com, broonie@kernel.org, mark.rutland@arm.com, keir@google.com, vdonnefort@google.com, kernel-team@android.com, android-mm@google.com, Catalin Marinas , Oliver Upton , Joey Gouly , Suzuki K Poulose , Zenghui Yu , Ard Biesheuvel , D Scott Phillips , Andrey Konovalov , Ankit Agrawal , Wang Jinchao , "Madhavan T. Venkataraman" , "=?UTF-8?q?Pierre-Cl=C3=A9ment=20Tosi?=" , Bjorn Helgaas , Ryan Roberts , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev Subject: Re: [PATCH] arm64: kvm: Make nvhe stack size configurable In-Reply-To: <20241108211446.3304809-1-kaleshsingh@google.com> References: <20241108211446.3304809-1-kaleshsingh@google.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/29.4 (aarch64-unknown-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: 185.219.108.64 X-SA-Exim-Rcpt-To: kaleshsingh@google.com, will@kernel.org, qperret@google.com, broonie@kernel.org, mark.rutland@arm.com, keir@google.com, vdonnefort@google.com, kernel-team@android.com, android-mm@google.com, catalin.marinas@arm.com, oliver.upton@linux.dev, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, ardb@kernel.org, scott@os.amperecomputing.com, andreyknvl@gmail.com, ankita@nvidia.com, wangjinchao@xfusion.com, madvenka@linux.microsoft.com, ptosi@google.com, bhelgaas@google.com, ryan.roberts@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev 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-20241110_030604_503317_9ED519BD X-CRM114-Status: GOOD ( 13.80 ) 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: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org [that's an impressive Cc list...] On Fri, 08 Nov 2024 21:14:00 +0000, Kalesh Singh wrote: > > In order to make the nVHE stack size easily configurable, > introduce NVHE_STACK_SHIFT which must be >= PAGE_SHIFT. > > The default stack size remains 1 page (no functional change) > > Downstream vendor features which require a larger stack > can configure it by setting CONFIG_NVHE_STACK_SHIFT. We don't let make the stack size configurable for the rest of the kernel, do we? Why should a tiny portion be treated differently? Making this configurable means that testing is harder, and bugs harder to reproduce. It also seems specially designed to allow badly written code to run in hypervisor context. And once you allow two pages to be used (up to 128kB), what prevents the "downstream vendor" to push this to 4 or 8? If anything, I would prefer to see this (obviously out of tree) code isolated with its own stack instead of growing EL2's private stack. At least this would make the problems attributable to the guilty party. Thanks, M. -- Without deviation from the norm, progress is not possible.