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 E105DC19F2E for ; Thu, 27 Feb 2025 10:47:47 +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=4NZ1Oq/YuEIf53+LhkyfhKnDuvuNyiJURkRanXDuAKk=; b=fFWXFcPGuPuAimCXCWfgvqwGpT QyrKff47PLJugLliPmYofNq4Ozn/7crOF4RUPh3r9Fx54W58LgKCcfJURZPRZuOXD+VUHDkxf86Rp /Z35ZFBRdOSapQX2EpeMpr/d3s92BF+ybPuL3816FRZSq+tgveRFTWP+LwDJMC6tryOePBykSQjAv VaU+xV1UpUwOBpz5nA37I+L0Rhl6zxv7eeDgTgtjaNStgbYquLcH1ATjPY2xOXfkBnLRWJgVPzRAW pg6pwSLQrheI+g1dYTtK5c8/vHPSPD+7smkD6YOIBohT0p37h3Qp5TPQIi6oYXnXz88FFAABBsU5p jpNalePA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tnbQU-000000072OE-2BbF; Thu, 27 Feb 2025 10:47:34 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tnbOx-0000000728d-0Ckn for linux-arm-kernel@lists.infradead.org; Thu, 27 Feb 2025 10:46:00 +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 F03E12BCC; Thu, 27 Feb 2025 02:46:08 -0800 (PST) Received: from [10.1.30.50] (e122027.cambridge.arm.com [10.1.30.50]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B6B373F673; Thu, 27 Feb 2025 02:45:48 -0800 (PST) Message-ID: Date: Thu, 27 Feb 2025 10:45:46 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 09/11] arm64: Enable memory encrypt for Realms To: Will Deacon , Catalin Marinas Cc: "Aneesh Kumar K . V" , Suzuki K Poulose , Marc Zyngier , James Morse , Oliver Upton , Zenghui Yu , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Joey Gouly , Alexandru Elisei , Christoffer Dall , Fuad Tabba , linux-coco@lists.linux.dev, Ganapatrao Kulkarni , Gavin Shan , Shanker Donthineni , Alper Gun , kvmarm@lists.linux.dev, kvm@vger.kernel.org References: <20241017131434.40935-1-steven.price@arm.com> <20241017131434.40935-10-steven.price@arm.com> <5aeb6f47-12be-40d5-be6f-847bb8ddc605@arm.com> <20250227002330.GA24899@willie-the-truck> From: Steven Price Content-Language: en-GB In-Reply-To: <20250227002330.GA24899@willie-the-truck> 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-20250227_024559_185403_528C2C0E X-CRM114-Status: GOOD ( 15.61 ) 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 27/02/2025 00:23, Will Deacon wrote: > On Wed, Feb 26, 2025 at 07:03:01PM +0000, Catalin Marinas wrote: >> On Wed, Feb 19, 2025 at 02:30:28PM +0000, Steven Price wrote: >>>> @@ -23,14 +25,16 @@ bool rodata_full __ro_after_init = IS_ENABLED(CONFIG_RODATA_FULL_DEFAULT_ENABLED >>>> bool can_set_direct_map(void) >>>> { >>>> /* >>>> - * rodata_full and DEBUG_PAGEALLOC require linear map to be >>>> - * mapped at page granularity, so that it is possible to >>>> + * rodata_full, DEBUG_PAGEALLOC and a Realm guest all require linear >>>> + * map to be mapped at page granularity, so that it is possible to >>>> * protect/unprotect single pages. >>>> * >>>> * KFENCE pool requires page-granular mapping if initialized late. >>>> + * >>>> + * Realms need to make pages shared/protected at page granularity. >>>> */ >>>> return rodata_full || debug_pagealloc_enabled() || >>>> - arm64_kfence_can_set_direct_map(); >>>> + arm64_kfence_can_set_direct_map() || is_realm_world(); >>>> } >>> >>> Aneesh pointed out that this call to is_realm_world() is now too early >>> since the decision to delay the RSI detection. The upshot is that a >>> realm guest which doesn't have page granularity forced for other reasons >>> will fail to share pages with the host. >>> >>> At the moment I can think of a couple of options: >>> >>> (1) Make rodata_full a requirement for realm guests. >>> CONFIG_RODATA_FULL_DEFAULT_ENABLED is already "default y" so this >>> isn't a big ask. >>> >>> (2) Revisit the idea of detecting when running as a realm guest early. >>> This has the advantage of also "fixing" earlycon (no need to >>> manually specify the shared-alias of an unprotected UART). >>> >>> I'm currently leaning towards (1) because it's the default anyway. But >>> if we're going to need to fix earlycon (or indeed find other similar >>> issues) then (2) would obviously make sense. >> >> I'd go with (1) since the end result is the same even if we implemented >> (2) - i.e. we still avoid block mappings in realms. > > Is it, though? The config option is about the default behaviour but there's > still an "rodata=" option on the command-line. I think the question comes down to is there any value in having page mappings and not setting the read-only permissions? I.e. rodata_full=false but we're still avoiding block mappings. (1) as I've currently proposed doesn't allow that combination - if you disable rodata_full you also break realms (assuming DEBUG_PAGEALLOC/kfence don't otherwise force can_set_direct_map(). (2) forces page mappings if there's an RMM present, but does allow disabling the read-only permissions with "rodata=". So I guess there's also another option: (3) Provide another compile/command line flag which forces page mapping which is different from rodata_full. That would then allow realms without affecting the permissions. or indeed: (4) Change can_set_direct_map() to always return true! ;) Thanks, Steve