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=-4.0 required=3.0 tests=BAYES_00,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 5BB7CC43381 for ; Mon, 8 Feb 2021 15:13:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 13BB264EF0 for ; Mon, 8 Feb 2021 15:13:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232073AbhBHPMe (ORCPT ); Mon, 8 Feb 2021 10:12:34 -0500 Received: from mail.kernel.org ([198.145.29.99]:52068 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232618AbhBHPD3 (ORCPT ); Mon, 8 Feb 2021 10:03:29 -0500 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 166F264E29; Mon, 8 Feb 2021 15:02:25 +0000 (UTC) Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.94) (envelope-from ) id 1l983S-00CoV5-QY; Mon, 08 Feb 2021 15:02:23 +0000 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Mon, 08 Feb 2021 15:02:22 +0000 From: Marc Zyngier To: Will Deacon Cc: Prasad Sodagudi , Srinivas Ramana , Catalin Marinas , Hector Martin , linux-kernel@vger.kernel.org, Ard Biesheuvel , Ajay Patil , kernel-team@android.com, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v7 00/23] arm64: Early CPU feature override, and applications to VHE, BTI and PAuth In-Reply-To: <20210208143248.GA25934@willie-the-truck> References: <20210208095732.3267263-1-maz@kernel.org> <20210208143248.GA25934@willie-the-truck> User-Agent: Roundcube Webmail/1.4.10 Message-ID: <240a0245f75d8368a4d90a5e6740dc7d@kernel.org> X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: will@kernel.org, psodagud@codeaurora.org, sramana@codeaurora.org, catalin.marinas@arm.com, marcan@marcan.st, linux-kernel@vger.kernel.org, ardb@kernel.org, pajay@qti.qualcomm.com, kernel-team@android.com, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org 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 Hi Will, On 2021-02-08 14:32, Will Deacon wrote: > Hi Marc, > > On Mon, Feb 08, 2021 at 09:57:09AM +0000, Marc Zyngier wrote: >> It recently came to light that there is a need to be able to override >> some CPU features very early on, before the kernel is fully up and >> running. The reasons for this range from specific feature support >> (such as using Protected KVM on VHE HW, which is the main motivation >> for this work) to errata workaround (a feature is broken on a CPU and >> needs to be turned off, or rather not enabled). >> >> This series tries to offer a limited framework for this kind of >> problems, by allowing a set of options to be passed on the >> command-line and altering the feature set that the cpufeature >> subsystem exposes to the rest of the kernel. Note that this doesn't >> change anything for code that directly uses the CPU ID registers. > > I applied this locally, but I'm seeing consistent boot failure under > QEMU when > KASAN is enabled. I tried sprinkling some __no_sanitize_address > annotations > around (see below) but it didn't help. The culprit appears to be > early_fdt_map(), but looking a bit more closely, I'm really nervous > about the > way we call into C functions from __primary_switched. Remember -- this > code > runs _twice_ when KASLR is active: before and after the randomization. > This > also means that any memory writes the first time around can be lost due > to > the D-cache invalidation when (re-)creating the kernel page-tables. Well, we already call into C functions with KASLR, and nothing explodes with that, so I must be doing something else wrong. I do have cache maintenance for the writes to the shadow registers, so that part should be fine. But I think I'm missing some cache maintenance around the FDT base itself, and I wonder what happens when we go around the loop. I'll chase this down now. Thanks for the heads up. M. -- Jazz is not dead. It just smells funny...