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=-16.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham 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 B44B6C432BE for ; Thu, 26 Aug 2021 13:33:50 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 82619608FE for ; Thu, 26 Aug 2021 13:33:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 82619608FE Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=LbVS8gPN/mjSRGD7HalD4jWvdd6xQ9pNn64mImyHhyI=; b=oLXcGXz1TY5Cve oP3Shwjmn2NobXHMzaymycWr/oEy5ENmVi/KblNDuL7le+QaW65srJGhtVKN2UdSnUj0sucFTrQZE 56M1N2576vFrr4DlOC40xYvT8+SEr6m59pVcG7dNBBqkLwDXsFzDbugEqAKfBrHMzS+5uD8meuqq3 53shc1COdhnU0WKObUHRdVbHRgnYwYnO0JevsmXSqD1/VYYnOrt9DWtXOVIhUHVX1KSHhrUivJNPG GK/K8U3s3MbtJ5WFg2lj24phEvcVW3XnDPo3Ge+zkoaFiiRXuHk8hFRUxe2qhaOKsuB/EHy64j7Ik EJFBQh0aU8c1V4Q3vWhg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mJFTe-00AFky-HC; Thu, 26 Aug 2021 13:31:30 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mJFTY-00AFjo-JC for linux-arm-kernel@lists.infradead.org; Thu, 26 Aug 2021 13:31:28 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id 1192060EE5; Thu, 26 Aug 2021 13:31:22 +0000 (UTC) Date: Thu, 26 Aug 2021 14:31:20 +0100 From: Catalin Marinas To: Will Deacon Cc: Ard Biesheuvel , linux-arm-kernel@lists.infradead.org, mark.rutland@arm.com, maz@kernel.org, anshuman.khandual@arm.com, steve.capper@arm.com Subject: Re: [RFC PATCH] arm64: mm: limit linear region to 51 bits for KVM in nVHE mode Message-ID: <20210826133118.GC30910@arm.com> References: <20210810161244.84231-1-ardb@kernel.org> <20210824105920.GB22752@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210824105920.GB22752@willie-the-truck> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210826_063124_693595_553A1DE1 X-CRM114-Status: GOOD ( 31.74 ) 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: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Aug 24, 2021 at 11:59:20AM +0100, Will Deacon wrote: > On Tue, Aug 10, 2021 at 06:12:44PM +0200, Ard Biesheuvel wrote: > > KVM in nVHE mode divides up its VA space into two equal halves, and > > picks the half that does not conflict with the HYP ID map to map its > > linear region. This worked fine when the kernel's linear map itself was > > guaranteed to cover precisely as many bits of VA space, but this was > > changed by commit f4693c2716b35d08 ("arm64: mm: extend linear region for > > 52-bit VA configurations"). > > > > The result is that, depending on the placement of the ID map, kernel-VA > > to hyp-VA translations may produce addresses that either conflict with > > other HYP mappings (including the ID map itself) or generate addresses > > outside of the 52-bit addressable range, neither of which is likely to > > lead to anything useful. > > > > Given that 52-bit capable cores are guaranteed to implement VHE, this > > only affects configurations such as pKVM where we opt into non-VHE mode > > even if the hardware is VHE capable. So just for these configurations, > > let's limit the kernel linear map to 51 bits and work around the > > problem. > > > > Fixes:f4693c2716b35d08 ("arm64: mm: extend linear region for 52-bit VA configurations") > > Signed-off-by: Ard Biesheuvel > > --- > > NOTE: build tested only > > > > arch/arm64/mm/init.c | 16 +++++++++++++++- > > 1 file changed, 15 insertions(+), 1 deletion(-) > > > > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c > > index 8490ed2917ff..542dad13e2fc 100644 > > --- a/arch/arm64/mm/init.c > > +++ b/arch/arm64/mm/init.c > > @@ -282,7 +282,21 @@ static void __init fdt_enforce_memory_region(void) > > > > void __init arm64_memblock_init(void) > > { > > - const s64 linear_region_size = PAGE_END - _PAGE_OFFSET(vabits_actual); > > + s64 linear_region_size = PAGE_END - _PAGE_OFFSET(vabits_actual); > > + > > + /* > > + * Corner case: 52-bit VA capable systems running KVM in nVHE mode may > > + * be limited in their ability to support a linear map that exceeds 51 > > + * bits of VA space, depending on the placement of the ID map. Given > > + * that the placement of the ID map may be randomized, let's simply > > + * limit the kernel's linear map to 51 bits as well if we detect this > > + * configuration. > > + */ > > + if (IS_ENABLED(CONFIG_KVM) && vabits_actual == 52 && > > + !is_kernel_in_hyp_mode()) { > > + pr_info("Capping linear region to 51 bits for KVM in nVHE mode on LVA capable hardware.\n"); > > + linear_region_size = BIT(51); > > + } > > Slight nit, but to avoid having to think about PAGE_END I think this would > be a little clearer as: > > if (IS_ENABLED(CONFIG_KVM) && !is_kernel_in_hyp_mode()) > linear_region_size = min_t(u64, linear_region_size, BIT(51)); BTW, do we also need to check is_hyp_mode_available() (instead of just CONFIG_KVM)? We don't need this reduction for a guest. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel