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 26446C19F30 for ; Wed, 26 Feb 2025 09:23:11 +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-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Ru3WUeEe8wKZUNQqs4sYz8QjMtxdS5poj9PYJGdyA1s=; b=PaaquwA78DJTkJEI5wWhWbPrTB nUz17hPMtViWTCKU4Z5yB0v1hze+MrVs4IclryheXezhgTu7Ns2XpEwY2x07t/AlreWXQPU6PzvTW 36AZ3BgeLSZD85Xjagrb0kHSQto8fZLjHQTQZ14ayIz61WQIHVNddmC2fP5doNVsBCrwwhr1I1w3z rM6ai2isUnqjAXln02XZkbUk0v0MptN8nUI1Dk6TZPybGZjcxiNJV/BRaGyjVVVxTL8SS3lkUKCpZ DCrva0GYs6Pel37zjxuAlR+u4JBKqZxyVIVQYMeYZOng13cx6pF3LvPKUSLHYXdBl07+0MJs8T57X XFs01fcw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tnDd6-000000033tb-1XRw; Wed, 26 Feb 2025 09:23:00 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tnDCW-00000002yjE-13fp for linux-arm-kernel@lists.infradead.org; Wed, 26 Feb 2025 08:55:33 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 777091063; Wed, 26 Feb 2025 00:55:47 -0800 (PST) Received: from [10.57.84.229] (unknown [10.57.84.229]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 523C43F6A8; Wed, 26 Feb 2025 00:55:30 -0800 (PST) Message-ID: Date: Wed, 26 Feb 2025 08:55:28 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1] arm64/mm: Fix Boot panic on Ampere Altra Content-Language: en-GB To: Ard Biesheuvel Cc: Will Deacon , Catalin Marinas , Mark Rutland , Luiz Capitulino , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20250225114638.2038006-1-ryan.roberts@arm.com> <20250226001047.GA24197@willie-the-truck> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250226_005532_349131_75CC7DF0 X-CRM114-Status: GOOD ( 23.43 ) 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 On 26/02/2025 08:33, Ard Biesheuvel wrote: > On Wed, 26 Feb 2025 at 09:07, Ryan Roberts wrote: >> >> On 26/02/2025 06:59, Ard Biesheuvel wrote: >>> On Wed, 26 Feb 2025 at 01:10, Will Deacon wrote: >>>> >>>> On Tue, Feb 25, 2025 at 07:05:35PM +0100, Ard Biesheuvel wrote: >>>>> Apologies for the breakage, and thanks for the fix. >>>>> >>>>> I have to admit that I was a bit overzealous here: there is no point >>>>> yet in using the sanitised value, given that we don't actually >>>>> override the PA range in the first place. >> >> But unless I've misunderstood something, parange is overridden; Commit >> 62cffa496aac (the same one we are fixing) adds an override to force parange to >> 48 bits when arm64.nolva is specified for LPA2 systems (see mmfr2_varange_filter()). >> >> I thought it would be preferable to honour that override, hence my use of >> arm64_apply_feature_override() in the fix. Are you saying we don't need to worry >> about that case? >> > > I wouldn't think so (but I'm glad you brought it up because this > didn't occur to me at all tbh) > > With arm64.nolva, both the VA and PA ranges will be reduced, and so > the range of the linear map will be 47 bits. So if the PA range is > being reduced from 52 to 48, it will still exceed the size of the > linear map, and so it should make no difference in this particular > case. OK, so I think you're saying it'll happen to work correctly even if we ignore that override? That sounds a bit fragile to me. Surely we should be consistent and either always honour the override or remove the override in the first place? > > The use case I had in mind was to allow the PA range to be reduced to > a value that is substantially less than the range of the linear map, > e.g, 40 bits on a 48-bit VA kernel. On the Android side, the issue of > the missing linear map randomization has come up a couple of times, > but there is no clear direction at this point, so adding this feature > here was premature (mea culpa)